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Built-In Collection Classes

 

Introduction to List Classes

 

Overview

Instead of creating a collection class from scratch or instead of deriving a collection, you can use one of the built-in collection classes of the .NET Framework. To support the creation of any kinds of list, the Microsoft .NET Framework provides the ArrayList and the generic List classes. 

The ArrayList class is defined in the System.Collections namespace while the generic List class is part of the System.Collections.Generic namespace. Therefore, in order to use one of these classes in your application, you can first include its namespace in the file that would perform the list-related operations.

The ArrayList class implements the IList, the ICollection, and the IEnumerable interfaces. The List class implements the generic IList<>, the generic ICollection<>, the generic IEnumerable<>, the IList, the ICollection, and the IEnumerable interfaces.

The ArrayList class is founded as follows:

public class ArrayList : IList,
			 ICollection,
			 IEnumerable, 
			 ICloneable

The generic List class is founded as follows:

public class List<T> : IList<T>,
		       ICollection<T>, 
		       IEnumerable<T>,
		       IList,
		       ICollection,
		       IEnumerable

You can use either the ArrayList or the generic List class to create and manage values for a list. Here is an example of declaring an ArrayList variable:

using System;
using System.Collections;
using System.Windows.Forms;

public class Exercise : Form
{
    ArrayList lstNames;

    public Exercise()
    {
        InitializeComponent();
    }

    void InitializeComponent()
    {
        Load += new EventHandler(StartForm);
    }

    void StartForm(object sender, EventArgs e)
    {
        lstNames = new ArrayList();
    }
}

public class Program
{
    static int Main()
    {
        System.Windows.Forms.Application.Run(new Exercise());
        return 0;
    }
}

Besides the ability to create a list, both the ArrayList and the List classes have the built-in mechanism for serialization.

The default constructor allows you to create an empty list before adding values to it. If you already have an ICollection-based list, that is, a list created from a class that implements the ICollection interface, you can initialize your ArrayList list with it. To support this, the ArrayList class is equipped with the following constructor:

public ArrayList(ICollection c);

Here is an example:

void StartForm(object sender, EventArgs e)
{
    ComboBox cbx = new ComboBox();
    cbx.Items.Add("Paul Bertrand Yamaguchi");
    cbx.Items.Add("Helene Mukoko");
    cbx.Items.Add("John Hancock");
    cbx.Items.Add("Gertrude Monay");

    lstNames = new ArrayList(cbx.Items);
}

Practical Learning Practical Learning: Introducing Built-In List Classes

  1. Start Microsoft Visual C# and create a new Windows Application named CollegeParkAutoParts1
  2. To create a dialog box, on the main menu, click Project -> Add Windows Form...
  3. Set the name to MakeEditor and click Add
  4. Design the form as follows:
     
    Make Editor
    Control Text Name Other Properties
    Label &Make:    
    TextBox   txtMake Modifiers: Public
    Button OK btnOK DialogResult: OK
    Button Cancel btnCancel DialogResult: Cancel
    Form Property Value
    FormBorderStyle FixedDialog
    Text Make Editor
    StartPosition CenterScreen
    AcceptButton btnOK
    CancelButton btnCancel
    MaximizeBox False
    MinimizeBox False
    ShowInTaskbar False
  5. To create a dialog box, on the main menu, click Project -> Add Windows Form...
  6. Set the name to ModelEditor and click Add
  7. Design the form as follows:
     
    College Park Auto Parts: Model Editor
    Control Text Name Other Properties
    Label &Model:    
    TextBox   txtModel Modifiers: Public
    Button OK btnOK DialogResult: OK
    Button Cancel btnCancel DialogResult: Cancel
    Form Property Value
    FormBorderStyle FixedDialog
    Text Model Editor
    StartPosition CenterScreen
    AcceptButton btnOK
    CancelButton btnCancel
    MaximizeBox False
    MinimizeBox False
    ShowInTaskbar False
  8. To create a dialog box, in the Solution Explorer, right-click CollegeParkAutoParts1 -> Add -> Windows Form...
  9. Set the name to CategoryEditor and click Add
  10. Design the form as follows:
     
    College Park Auto Parts: Category Editor
    Control Text Name Other Properties
    Label &Category:    
    TextBox   txtCategory Modifiers: Public
    Button OK btnOK DialogResult: OK
    Button Cancel btnCancel DialogResult: Cancel
    Form Property Value
    FormBorderStyle FixedDialog
    Text Category Editor
    StartPosition CenterScreen
    AcceptButton btnOK
    CancelButton btnCancel
    MaximizeBox False
    MinimizeBox False
    ShowInTaskbar False
  11. On the main menu, click Project -> Add Windows Form...
  12. Set the Name to NewStoreItem and click Add
  13. Design the form as follows:
     
    College Park Auto-Part - Part Editor
     
    Control Text Name Other Properties
    Label &Year:    
    TextBox   txtItemNumber  
    Label &Make:    
    ComboBox   cbxMakes  
    Button New C&ategory... btnNewMake  
    Label M&odel:    
    ComboBox   cbxModels  
    Button New Mo &del... btnNewModel  
    Label &Category:    
    ComboBox   cbxCategories  
    Button New Ca&tegory btnNewCategory  
    Label &Unit Price:    
    TextBox 0.00 txtUnitPrice TextAlign: Right
    Label Part #:    
    TextBox   txtPartNumber  
    Label &Part Name:    
    TextBox   txtPartName  
    Button Submit btnSubmit  
    Button Close btnClose DialogResult: Cancel
    Form Property Value
    FormBorderStyle FixedDialog
    Text College Park Auto -Parts: Part Editor
    StartPosition CenterScreen
    MaximizeBox False
    MinimizeBox False
    ShowInTaskbar False
  14. Double-click the New Make button and implement it as follows:
      
    private void btnNewMake_Click(object sender, EventArgs e)
    {
        var editor = new MakeEditor();
    
        if (editor.ShowDialog() == DialogResult.OK)
        {
            if (editor.txtMake.Text.Length > 0)
            {
                var strMake = editor.txtMake.Text;
    
                // Make sure the category is not yet in the list
                if (cbxMakes.Items.Contains(strMake))
                    MessageBox.Show(strMake + " is already in the list");
                else
                {
                    // Since this is a new category, add it to the combo box
                    cbxMakes.Items.Add(strMake);
                }
                        
                cbxMakes.Text = strMake;
            }
        }
    }
  15. Return to the Part Editor dialog box and double-click the New Model button
  16. Implement the event as follows:
      
    private void btnNewModel_Click(object sender, EventArgs e)
    {
        var editor = new ModelEditor();
    
        if (editor.ShowDialog() == DialogResult.OK)
        {
            if (editor.txtModel.Text.Length > 0)
            {
                var strModel = editor.txtModel.Text;
    
                // Make sure the category is not yet in the list
                if (cbxModels.Items.Contains(strModel))
                    MessageBox.Show(strModel + " is already in the list");
                else
                {
                    // Since this is a new category, add it to the combo box
                    cbxModels.Items.Add(strModel);
                }
    
                cbxModels.Text = strModel;
            }
        }
    }
  17. Return to the Part Editor dialog box and double-click the New Category button
  18. Implement the event as follows:
      
    private void btnNewCategory_Click(object sender, EventArgs e)
    {
        var editor = new CategoryEditor();
    
        if (editor.ShowDialog() == DialogResult.OK)
        {
            if (editor.txtCategory.Text.Length > 0)
            {
                var strCategory = editor.txtCategory.Text;
    
                // Make sure the category is not yet in the list
                if (cbxCategories.Items.Contains(strCategory))
                    MessageBox.Show(strCategory + " is already in the list");
                else
                {
                    // Since this is a new category, add it to the combo box
                    cbxCategories.Items.Add(strCategory);
                }
                
                cbxCategories.Text = strCategory;
            }
        }
    }
  19. Save the file and close the form
  20. To create an icon, on the main menu, click Project -> Add New Item...
  21. In the Templates list, click Icon File
  22. Set the Name to cpap1 and click Add
  23. Right-click the white area and click Delete Image Type
  24. Design the 16x16, 16 colors version of the icon as follows:
     
  25. On the main menu, click File -> Save cpap1.ico As
  26. Select the bin\Debug folder of the current folder and click Save
  27. On the main menu, click File -> Close
  28. In the Solution Explorer, expand bin and expand Debug
  29. In the Solution Explorer, right-click the Debug folder -> Add -> New Item...
  30. In the Templates list, make sure Icon File is selected.
    Set the Name to cpap2 and click Add
  31. Right-click the white area and click Delete Image Type
  32. Design the 16x16, 16 colors version of the icon as follows:
     
  33. Save the file and close the icon window
  34. In the Solution Explorer, right- click the Debug folder -> Add -> New Item...
  35. In the Templates list, make sure Icon File is selected.
    Set the Name to year1 and click Add
  36. Right-click the white area and click Delete Image Type
  37. Design the 16x16, 16 colors version of the icon as follows:
     
  38. Save the file and close the icon window
  39. In the Solution Explorer, right- click the Debug folder -> Add -> New Item...
  40. In the Templates list, make sure Icon File is selected.
    Set the Name to year2 and click Add
  41. Right-click the white area and click Delete Image Type
  42. Design the 16x16, 16 colors version of the icon as follows:
     
  43. Save the file and close the icon window
  44. In the Solution Explorer, right- click the Debug folder -> Add -> New Item...
  45. In the Templates list, make sure Icon File is selected.
    Set the Name to make1 and click Add
  46. Right-click the white area and click Delete Image Type
  47. Design the 16x16, 16 colors version of the icon as follows:
     
    Icon Design: Diamond
  48. Save the file and close the icon window
  49. In the Solution Explorer, right- click the Debug folder -> Add -> New Item...
  50. In the Templates list, make sure Icon File is selected.
    Set the Name to make2 and click Add
  51. Right-click the white area and click Delete Image Type
  52. Design the 16x16, 16 colors version of the icon as follows:
     
    Icon Design: Diamond
  53. Save the file and close the icon window
  54. In the Solution Explorer, right- click the Debug folder -> Add -> New Item...
  55. In the Templates list, make sure Icon File is selected.
    Set the Name to model1 and click Add
  56. Right-click the white area and click Delete Image Type
  57. Design the 16x16, 16 colors version of the icon as follows:
     
  58. Save the file and close the icon window
  59. In the Solution Explorer, right- click the Debug folder -> Add -> New Item...
  60. In the Templates list, make sure Icon File is selected.
    Set the Name to model2 and click Add
  61. Right-click the white area and click Delete Image Type
  62. Design the 16x16, 16 colors version of the icon as follows:
     
  63. Save the file and close the icon window
  64. In the Solution Explorer, right- click the Debug folder -> Add -> New Item...
  65. In the Templates list, make sure Icon File is selected.
    Set the Name to category1 and click Add
  66. Right-click the white area and click Delete Image Type
  67. Design the 16x16, 16 colors version of the icon as follows:
     
  68. Save the file and close the icon window
  69. In the Solution Explorer, right- click the Debug folder -> Add -> New Item...
  70. In the Templates list, make sure Icon File is selected.
    Set the Name to category2 and click Add
  71. Right-click the white area and click Delete Image Type
  72. Design the 16x16, 16 colors version of the icon as follows:
     
    Icon Design: Minus
  73. Save the file and close the icon window
  74. In the Solution Explorer, right-click Form1.cs and click Rename
  75. Type Central.cs and press Enter twice to display the Central form
  76. From the Components section of the Toolbox, click ImageList and click the form
  77. In the Properties window, click (Name) and type AutoPartsImages
  78. Click the ellipsis button of the Images field
  79. In the Image Collection Editor, click Add
  80. Locate the folder that contains the icons you created and display it in the Look In combo box
  81. Select cpap1.ico and click Open
  82. In the same way, add the other pictures in the following order: cpap2.ico, year1.ico, year2.ico, make1.ico, make2.ico, model1.ico, model2.ico, category1.ico, and category1.ico
     
    Image Collection Editor
  83. Click OK
  84. Design the form as follows:
     
    College Park Auto Parts - Form Design
    Control Text Name Other Properties
    Label Label College Park Auto-Parts   Font: Times New Roman, 20.25pt, style=Bold
    ForeColor: Blue
    Panel     Height: 2
    GroupBox GroupBox Part Identification    
    TreeView TreeView   tvwAutoParts ImageList: imgAutoParts
    GroupBox GroupBox Available Parts    
    ListView ListView   lvwAutoParts FullRowSelect: True
    GridLines: True
    View: Details
    Columns   (Name) Text TextAlign Width
    colPartNumber Part #    
    colPartName Part Name   300
    colUnitPrice Unit Price Right 80
    GroupBox GroupBox Customer Order - Selected Parts    
    Label Label Part #    
    Label Label Part Name    
    Label Label Unit Price    
    Label Label Qty    
    Label Label Sub Total    
    TextBox TextBox   txtPartNumber  
    TextBox TextBox   txtPartName  
    TextBox TextBox 0.00 txtUnitPrice TextAlign: Right
    TextBox TextBox 0 txtQuantity TextAlign: Right
    TextBox TextBox 0.00 txtSubTotal TextAlign: Right
    Button Button Add/Select btnAdd
    ListView ListView   lvwSelectedParts FullRowSelect: True
    GridLines: True
    View: Details
    Columns   (Name) Text TextAlign Width
    colPartNumberSelected Part #   45
    colPartNameSelected Part Name   274
    colUnitPriceSelected Unit Price Right 58
    colQuantitySelected Qty Right 28
    colSubTotalSelected Sub-Total Right 58
    GroupBox GroupBox Order Summary
    Button Button New Au&to Part... btnNewAutoPart  
    Label Label Receipt #:  
    TextBox TextBox txtSave
    Button Button Save btnSave
    Label Label Tax Rate:
    TextBox TextBox 7.75 txtTaxRate TextAlign: Right
    Label Label %
    Label Label Parts Total:
    TextBox TextBox 0.00 txtPartsTotal TextAlign: Right
    Button Button &New Customer Order btnNewCustomerOrder  
    Label Label Receipt #:  
    TextBox TextBox txtOpen
    Button Button Save btnOpen
    Label Label Tax Amount:
    TextBox TextBox 0.00 txtTaxAmount TextAlign: Right
    Label Label Order Total:
    TextBox TextBox 0.00 txtOrderTotal TextAlign: Right
    Button Button Close btnClose  
  85. Click the Available Parts list view
  86. In the Properties window, click the Events button and, in the Events section, double-click DoubleClick
  87. Implement the event as follows:
     
    private void lvwAutoParts_DoubleClick(object sender, EventArgs e)
    {
        var lviAutoPart = lvwAutoParts.SelectedItems[0];
    
        if( (lvwAutoParts.SelectedItems.Count == 0) ||
            (lvwAutoParts.SelectedItems.Count > 1) )
                    return;
    
        txtPartNumber.Text = lviAutoPart.Text;
        txtPartName.Text = lviAutoPart.SubItems[1].Text;
        txtUnitPrice.Text = lviAutoPart.SubItems[2].Text;
    
        txtQuantity.Text = "1";
        txtSubTotal.Text = lviAutoPart.SubItems[2].Text;
    
        txtQuantity.Focus();
    }
  88. Return to the Central form
  89. Click the Unit Price text box and, in the Events section of the Properties window, double-click Leave
  90. Implement the event as follows:
     
    private void txtUnitPrice_Leave(object sender, EventArgs e)
    {
        var UnitPrice = 0.00D;
        var Quantity = 0;
        var SubTotal = 0.00D;
    
        try
        {
            UnitPrice = double.Parse(txtUnitPrice.Text);
        }
        catch (FormatException)
        {
            MessageBox.Show("Invalid Unit Price!");
        }
    
        try { Quantity = int.Parse(txtQuantity.Text); }
        catch (FormatException)
        {
            MessageBox.Show("Invalid Quandtity!");
        }
    
        SubTotal = UnitPrice * Quantity;
        txtSubTotal.Text = SubTotal.ToString("F");
    }
    
    internal void CalculateOrder()
    {
        // Calculate the current total order and update the order
        var PartsTotal = 0.00D;
        var TaxRate = 0.00D;
        var TaxAmount = 0.00D;
        var OrderTotal = 0.00D;
                
        foreach (ListViewItem lvi in lvwSelectedParts.Items)
        {
            ListViewItem.ListViewSubItem SubItem = lvi.SubItems[4];
            PartsTotal += double.Parse(SubItem.Text);
        }
    
        try
        {
            TaxRate = double.Parse(txtTaxRate.Text) / 100;
        }
        catch (FormatException)
        {
            MessageBox.Show("Invalid Tax Rate");
        }
    
        TaxAmount = PartsTotal * TaxRate;
        OrderTotal = PartsTotal + TaxAmount;
    
        txtPartsTotal.Text = PartsTotal.ToString("F");
        txtTaxAmount.Text = TaxAmount.ToString("F");
        txtOrderTotal.Text = OrderTotal.ToString("F");
    }
  91. Return to the Central form and click the Qty text box
  92. In the Events section of the Properties, click Leave, then click the arrow of its combo box and select txtUnitPrice_Leave
  93. Return to the Central form
  94. Click the Available Parts list view (the list view in the bottom-right section of the form)
  95. In the Events section of the Properties window, double-click DoubleClick
  96. Implement the event as follows:
     
    private void lvwSelectedParts_DoubleClick(object sender, EventArgs e)
    {
        var lviSelectedPart = lvwSelectedParts.SelectedItems[0];
    
        if( (lvwSelectedParts.SelectedItems.Count == 0) ||
            (lvwSelectedParts.SelectedItems.Count > 1) )
            return;
    
        txtPartNumber.Text = lviSelectedPart.Text;
        txtPartName.Text = lviSelectedPart.SubItems[1].Text;
        txtUnitPrice.Text = lviSelectedPart.SubItems[2].Text;
        txtQuantity.Text = lviSelectedPart.SubItems[3].Text;
        txtSubTotal.Text = lviSelectedPart.SubItems[4].Text;
    
        lvwSelectedParts.Items.Remove(lviSelectedPart);
        CalculateOrder();
    }
  97. In the Solution Explorer, right-click CollegeParkAutoParts1 -> Add -> Class...
  98. Set the name to PartDescription and press Enter
  99. To create a class that can hold a structured item of a list, change the class as follows:
     
    using System;
    using System.Collections.Generic;
    using System.Linq;
    using System.Text;
    
    namespace CollegeParkAutoParts1
    {
        [Serializable]
        public class PartDescription
        {
            // These members will be used to define a car part
            private long ID;
            private int yr;
            private string mk;
            private string mdl;
            private string cat;
            private string name;
            private double price;
    
            public PartDescription()
            {
                this.ID = 0;
                this.yr = 1960;
                this.mk = "";
                this.mdl = "";
                this.name = "Unknown";
                this.price = 0.00;
            }
    
            public PartDescription(long code, int year, string make,
                                   string model, string type,
                                   string desc, double UPrice)
            {
                this.ID = code;
                this.yr = year;
                this.mk = make;
                this.mdl = model;
                this.cat = type;
                this.name = desc;
                this.price = UPrice;
            }
    
            public long PartNumber
            {
                get { return ID; }
                set { ID = value; }
            }
    
            public int Year
            {
                get { return yr; }
                set { yr = value; }
            }
    
            public string Make
            {
                get { return mk; }
                set { mk = value; }
            }
    
            public string Model
            {
                get { return mdl; }
                set { mdl = value; }
            }
    
            public string Category
            {
                get { return cat; }
                set { cat = value; }
            }
    
            public string PartName
            {
                get { return name; }
                set { name = value; }
            }
    
            public double UnitPrice
            {
                get { return (price < 0) ? 0.00 : price; }
                set { price = value; }
            }
    
            public override string ToString()
            {
                return this.PartNumber + " " +
                       this.Year.ToString() + " " +
                       this.Make + " " +
                       this.Model + " " +
                       this.Category + " " +
                       this.PartName + " " +
                       this.UnitPrice;
            }
        }
    }
  100. In the Solution Explorer, right-click CollegeParkAutoParts1 -> Add -> Class...
  101. Set the name to PartsOrdered and press Enter
  102. To create another class independent for a list, change the document as follows:
     
    using System;
    using System.Collections.Generic;
    using System.Linq;
    using System.Text;
    
    namespace CollegeParkAutoParts1
    {
        [Serializable]
        public class PartsOrdered
        {
            public long PartNumber;
            public string PartName;
            public double UnitPrice;
            public int Quantity;
            public double SubTotal;
        }
    }
  103. Save all

The Capacity of a List

After declaring an ArrayList or a List variable, it is empty. As objects are added to it, the list grows. The list can grow tremendously as you wish. The number of items of the list is managed through the memory it occupies and this memory grows as needed. The number of items that the memory allocated is currently using is represented by the Capacity property. Here is an example of accessing the ArrayList.Capacity property:

public class Exercise : Form
{
    ArrayList lstNames;

    public Exercise()
    {
        InitializeComponent();
    }

    void InitializeComponent()
    {
        Load += new EventHandler(StartForm);
    }

    void StartForm(object sender, EventArgs e)
    {
        lstNames = new ArrayList();
        Text = "List Capacity: " + lstNames.Capacity.ToString();
    }
}

This would produce:

ArrayList Capacity

The capacity of a list will usually be the least of your concerns. If for some reason, you want to intervene and control the number of items that your list can contain, you can manipulate the Capacity property. For example, you can assign it a constant to set the maximum value that the list can contain. Instead of specifying the capacity after the list has been created, when declaring the list variable, you can specify its maximum capacity. To support this, both the ArrayList and the List classes are equipped with an additional constructor as follows:

public ArrayList(int capacity);
public List(int capacity);

Once again, you will hardly have any reason to use the Capacity property: the compiler knows what to do with it.

A Read-Only List

One of the reason for creating a list is to be able to add values to it, edit its values, retrieve a value, or delete values from it. These are the default operations. You can still limit these operations as you judge them unnecessary. For example, you may create a list and then initialize it with the values that you want the list to only have. If you do not want to have the user adding values to it, you can create the list as read-only. To do this, you can call the ArrayList.ReadOnly() method. It is overloaded with two versions as follows:

Public Shared Function ReadOnly(list As ArrayList) As ArrayList
public static IList ReadOnly(IList list)

Some operations cannot be performed on a read-only list. To perform such operations, you can first find out whether an ArrayList list is read-only. This is done by checking its IsReadOnly property.

Item Addition

The primary operation performed on a list is to create one or more values. To do this, you have various alternatives. Both the ArrayList and the List classes are equipped with an Add() method. The syntax of the System.Collections.ArrayList.Add() method is:

public virtual int Add(object value);

The syntax of the System.Collections.Generic.List.Add() method is:

public void Add(T value);

The argument of the method is the value to add to the list. If the method succeeds with the addition, it returns the position where the value was added in the list. Here are example for an ArrayList variable:

void StartForm(object sender, EventArgs e)
{
    Text = "Employees Records";

    lstNames = new ArrayList();

    lstNames.Add("Christine Kingston");
    lstNames.Add("Hermine Paulson");
    lstNames.Add("William Harrison");
    lstNames.Add("Ursula Morales");
    lstNames.Add("Evan Lancos");
}

If the method fails to add the value and if you are using the ArrayList class, the compiler would throw an error. One of the errors that could result from the ArrayList's failure of this operation would be based on the fact that either a new value cannot be added to the list because the list is read-only, or the list was already full prior to adding the new value. Normally, a list can be full only if you had specified the maximum number of items it can contain using the ArrayList.Capacity property. As mentioned above, the list can be made read-only by passing its variable to the ArrayList.ReadOnly() method.

Instead of adding one values at a time, you can first create a list of values and add that whole list at once. To support this operation, both the ArrayList and the List classes are equipped with a method named AddRange.

The syntax of the ArrayList.AddRange() method is:

public virtual void AddRange(ICollection collection);

The syntax of the List.AddRange() method is:

public void AddRange(IEnumerable<T> collection);

The ArrayList.AddRange() method takes as argument a list created from a class that implements the ICollection interface. Here is an example:

void StartForm(object sender, EventArgs e)
{
    Text = "Employees";

    ComboBox cbx = new ComboBox();
    cbx.Items.Add("Paul Bertrand Yamaguchi");
    cbx.Items.Add("Helene Mukoko");
    cbx.Items.Add("John Hancock");
    cbx.Items.Add("Gertrude Monay");

    lstNames = new ArrayList();
    lstNames.AddRange(cbx.Items);
}

The List.AddRange() method takes as argument a list created from a class that implements the generic IEnumerable interface.

Practical Learning Practical Learning: Adding Items to an ArrayList List

  1. Display the Part Editor form and double-click the Submit button
  2. Implement the event as follows:
     
    using System;
    using System.Collections.Generic;
    using System.ComponentModel;
    using System.Data;
    using System.Drawing;
    using System.Linq;
    using System.Text;
    using System.Windows.Forms;
    using System.IO;
    using System.Runtime.Serialization.Formatters.Binary;
    
    namespace CollegeParkAutoParts1
    {
        public partial class NewStoreItem : Form
        {
            List<PartDescription> lstAutoParts;
    
            . . . No Change
    
            private void btnSubmit_Click(object sender, EventArgs e)
            {
                FileStream stmAutoParts = null;
                BinaryFormatter bfmAutoParts = new BinaryFormatter();
    
                // If this directory doesn't exist, create it
                Directory.CreateDirectory(@"C:\College Park Auto Parts");
                // This is the file that holds the list of items
                string FileName = @"C:\College Park Auto Parts\Parts.prs";
    
                // Create a random number that will be used to identify the item
                Random rnd = new Random();
                txtPartNumber.Text = rnd.Next(100000, 999999).ToString();
    
                // Make sure the user had selected a make
                if (cbxYears.Text.Length == 0)
                {
                    MessageBox.Show("You must specify the year");
                    cbxYears.Focus();
                    return;
                }
    
                // Make sure the user had selected a make
                if (cbxMakes.Text.Length == 0)
                {
                    MessageBox.Show("You must specify the car name");
                    cbxMakes.Focus();
                    return;
                }
    
                // Make sure the user had selected a model
                if (cbxModels.Text.Length == 0)
                {
                    MessageBox.Show("You must specify the model of the car");
                    cbxModels.Focus();
                    return;
                }
    
                // Make sure the user had selected the part category
                if (cbxCategories.Text.Length == 0)
                {
                    MessageBox.Show("You must specify the part's category");
                    cbxCategories.Focus();
                    return;
                }
    
                // Make sure the user had entered a name/description
                if (txtPartName.Text.Length == 0)
                {
                    MessageBox.Show("You must enter the name (or a " +
                                    "short description) for the part");
                    txtPartName.Focus();
                    return;
                }
    
                // Make sure the user had typed a price for the item
                if (txtUnitPrice.Text.Length == 0)
                {
                    MessageBox.Show("You must enter the price of the item");
                    txtUnitPrice.Focus();
                    return;
                }
    
                // Before saving the new part, find out if there was
                // already a file that holds the list of parts
                // If that file exists, open it and store its parts 
                // in our lstParts variable
                if (File.Exists(FileName))
                {
                    stmAutoParts = new FileStream(FileName,
                                                  FileMode.Open,
                                                  FileAccess.Read,
                                                  FileShare.Read);
    
                    try
                    {
                        // Retrieve the list of items from file
                        lstAutoParts =
                            (List<PartDescription>)bfmAutoParts.Deserialize(stmAutoParts);
                    }
                    finally
                    {
                        stmAutoParts.Close();
                    }
                }
    
                // Create the part
                PartDescription part = new PartDescription();
                part.PartNumber = long.Parse(txtPartNumber.Text);
                part.Year = int.Parse(cbxYears.Text);
                part.Make = cbxMakes.Text;
                part.Model = cbxModels.Text;
                part.Category = cbxCategories.Text;
                part.PartName = txtPartName.Text;
                part.UnitPrice = double.Parse(txtUnitPrice.Text);
    
                // Call the Add method of our collection class to add the part
                lstAutoParts.Add(part);
    
                // Save the list
                stmAutoParts = new FileStream(FileName,
                                              FileMode.Create,
                                              FileAccess.Write,
                                              FileShare.Write);
    
                try
                {
                    bfmAutoParts.Serialize(stmAutoParts, lstAutoParts);
    
                    // After saving the item, reset the form
                    cbxYears.Text = "";
                    cbxMakes.Text = "";
                    cbxModels.Text = "";
                    cbxCategories.Text = "";
                    txtPartName.Text = "";
                    txtUnitPrice.Text = "0.00";
                    txtPartNumber.Text = rnd.Next(100000, 999999).ToString();
                }
                finally
                {
                    stmAutoParts.Close();
                }
            }
        }
    }
  3. In the Solution Explorer, right-click Central.cs and click View Code
  4. Add the following namespaces in the top section of the file:
     
    using System;
    using System.Collections.Generic;
    using System.ComponentModel;
    using System.Data;
    using System.Drawing;
    using System.Linq;
    using System.Text;
    using System.Windows.Forms;
    using System.IO;
    using System.Runtime.Serialization.Formatters.Binary;
  5. Return to the Central form and double-click the Save Customer Order button
  6. Implement its event as follows:
     
    private void btnSaveCustomerOrder_Click(object sender, EventArgs e)
    {
        BinaryFormatter bfmCustomerOrder = new BinaryFormatter();
    
        // We will store our files in the following folder    
        string strDirectory = @"C:\College Park Auto Parts\Receipts";
        DirectoryInfo dirInfo = new DirectoryInfo(strDirectory);
    
        string strFilename = strDirectory + "\\" + txtSave.Text + ".cap";
    
        List<PartsOrdered> lstOrderedParts = null;
    
        if (lvwSelectedParts.Items.Count == 0)
            return;
        else
        {
            lstOrderedParts = new List<PartsOrdered>();
    
            for (int i = 0; i < lvwSelectedParts.Items.Count; i++)
            {
                PartsOrdered part = new PartsOrdered();
    
                part.PartNumber = long.Parse(lvwSelectedParts.Items[i].Text);
                part.PartName = lvwSelectedParts.Items[i].SubItems[1].Text;
                part.UnitPrice = double.Parse(lvwSelectedParts.Items[i].SubItems[2].Text);
                part.Quantity = int.Parse(lvwSelectedParts.Items[i].SubItems[3].Text);
                part.SubTotal = double.Parse(lvwSelectedParts.Items[i].SubItems[4].Text);
                lstOrderedParts.Add(part);
            }
    
            FileStream stmCustomerOrder = new FileStream(strFilename, FileMode.Create);
    
            try
            {
                bfmCustomerOrder.Serialize(stmCustomerOrder, lstOrderedParts);
            }
            finally
            {
                stmCustomerOrder.Close();
            }
        }
    }
  7. Save all

The Number of Items in the List

When using a list, at any time, you should be able to know the number of items that the list contains. This information is provided by the ArrayList.Count or the List.Count property.

The Capacity and the Count properties have this in common: the value of each increases as the list grows and the same value decreases if the list shrinks. It is important to know that there are various differences between the capacity of a list and the number of items it contains. Capacity is a read/write property. This means that you can assign a value to the capacity to fix the number of items that the list can contain. You can also retrieve the value of the Capacity. The Count property is read-only because it is used by the compiler to count the current number of values of the list and this counting is performed without your intervention.

Item Retrieval

Once a list is ready, you can perform different types of operations on it. Besides adding items, one of the most regular operations performed on a list consists of locating and retrieving its values. You have various options.

To give you access to each member of their list, both the ArrayList and the List classes are equipped with the default Item property. The Item property is an indexer. The first value of the list has an index of 0. The second has an index of 1, and so on. 

To retrieve a single value based on its position, you can apply the square brackets of arrays to the variable. Here is an example:

using System;
using System.Drawing;
using System.Collections;
using System.Windows.Forms;

public class Exercise : Form
{
    ArrayList lstNames;
    ListBox lbxNames;

    public Exercise()
    {
        InitializeComponent();
    }

    void InitializeComponent()
    {
        lbxNames = new ListBox();
        lbxNames.Location = new Point(12, 12);
        Controls.Add(lbxNames);

        Load += new EventHandler(StartForm);
    }

    void StartForm(object sender, EventArgs e)
    {
        Text = "Employees";

        lstNames = new ArrayList();

        lstNames.Add("Christine Kingston");
        lstNames.Add("Hermine Paulson");
        lstNames.Add("William Harrison");
        lstNames.Add("Ursula Morales");
        lstNames.Add("Evan Lancos");

        for (int i = 0; i < 5; i++)
            lbxNames.Items.Add(lstNames[i]);
    }
}

public class Program
{
    static int Main()
    {
        System.Windows.Forms.Application.Run(new Exercise());
        return 0;
    }
}

ArrayList

Another issue to keep in mind is that the ArrayList[] indexer returns an Object value. Therefore, you may have to cast this value to your type of value to get it right.

Besides using the index to access a value from the list, the ArrayList and the List classes implement the IEnumerable.GetEnumerator() method. For this reason, you can use the foreach loop to access each member of the collection. Here is an example:

void StartForm(object sender, EventArgs e)
{
    Text = "Employees";

    lstNames = new ArrayList();

    lstNames.Add("Christine Kingston");
    lstNames.Add("Hermine Paulson");
    lstNames.Add("William Harrison");
    lstNames.Add("Ursula Morales");
    lstNames.Add("Evan Lancos");

    foreach (string str in lstNames)
        lbxNames.Items.Add(str);
}

You can use the Item property to change a value in the list. Because the Item property is used to access an existing value from the list, the value must have been created. If you try setting the value of a non existing item, the compiler would throw an ArgumentOutOfRangeException Exception. Here is an example:

void StartForm(object sender, EventArgs e)
{
    Text = "Employees";

    lstNames = new ArrayList();

    lstNames[0] = "Paul Bertrand Yamaguchi";
}

Notice that at the time the 0 item is accessed, it has not previous been created. This would produce:

Error

A review of the Details section shows:

System.ArgumentOutOfRangeException: Index was out of range. 
Must be non-negative and less than the size of the collection.
Parameter name: index
at System.Collections.ArrayList.set_Item(Int32 index, Object value)
at Exercise.StartForm(Object sender, EventArgs e) 
in E:\Programs\VCSharp\Exercise1\Exercise1\Exercise.cs:line 31

This means that you can use the Item property only to change the value of a previous created item.

Practical Learning Practical Learning: Enumerating a List

  1. Display the Part Editor form and double-click the Makes combo box
  2. Implement its SelectedIndexChanged event as follows:
     
    private void cbxMakes_SelectedIndexChanged(object sender, EventArgs e)
    {
        cbxModels.Text = "";
        cbxModels.Items.Clear();
    
        foreach (PartDescription part in lstAutoParts)
            if (part.Make == cbxMakes.Text)
                if (!cbxModels.Items.Contains(part.Model))
                    cbxModels.Items.Add(part.Model);
    }
  3. Display the Central form and double-click the Add/Select button
  4. Implement the event as follows:
     
    private void btnAdd_Click(object sender, EventArgs e)
    {
        if (txtPartNumber.Text.Length == 0)
        {
            MessageBox.Show("There is no part to be added to the order");
            return;
        }
    
        foreach (PartDescription part in lstAutoParts)
        {
            if (part.PartNumber == long.Parse(txtPartNumber.Text))
            {
                ListViewItem lviSelectedPart =
    		new ListViewItem(part.PartNumber.ToString());
    
                lviSelectedPart.SubItems.Add(part.PartName);
                lviSelectedPart.SubItems.Add(part.UnitPrice.ToString());
                lviSelectedPart.SubItems.Add(txtQuantity.Text);
                lviSelectedPart.SubItems.Add(txtSubTotal.Text);
                lvwSelectedParts.Items.Add(lviSelectedPart);
            }
        }
    
        CalculateOrder();
    }
  5. Return to the Central form and double-click the Open button
  6. Implement its event as follows:
     
    private void btnOpen_Click(object sender, EventArgs e)
    {
        List<PartsOrdered> lstReceipts = null;
        BinaryFormatter bfmReceipts = new BinaryFormatter();
        FileStream stmReceipts = null;
    
        string strDirectory = @"C:\College Park Auto Parts\Receipts";
        string strFilename = "";
    
        DirectoryInfo dirReceipts = new DirectoryInfo(strDirectory);
        FileInfo[] fleReceipts = dirReceipts.GetFiles();
    
        if (txtOpen.Text.Length == 0)
        {
            MessageBox.Show("You must enter a receipt number\n" +
                            "There is no receipt number to " +
                            "open a customer's order");
            txtOpen.Focus();
            return;
        }
    
        if (fleReceipts.Length == 0)
        {
            MessageBox.Show("There is no customer order to open");
            txtOpen.Focus();
            return;
        }
        else
        {
            lvwAutoParts.Items.Clear();
            lvwSelectedParts.Items.Clear();
    
            strFilename = strDirectory + "\\" + txtOpen.Text + ".cap";
    
            if (File.Exists(strFilename))
            {
                try
                {
                    stmReceipts = new FileStream(strFilename, FileMode.Open);
                    lstReceipts =
    			(List<PartsOrdered>)bfmReceipts.Deserialize(stmReceipts);
    
                    foreach (PartsOrdered part in lstReceipts)
                    {
                        ListViewItem lviReceiptPart =
    			new ListViewItem(part.PartNumber.ToString());
    
                        lviReceiptPart.SubItems.Add(part.PartName);
                        lviReceiptPart.SubItems.Add(part.UnitPrice.ToString());
                        lviReceiptPart.SubItems.Add(part.Quantity.ToString());
                        lviReceiptPart.SubItems.Add(part.SubTotal.ToString());
                        lvwSelectedParts.Items.Add(lviReceiptPart);
                    }
                }
                finally
                {
                    stmReceipts.Close();
                }
    
                CalculateOrder();
                txtSave.Text = txtOpen.Text;
            }
            else
                MessageBox.Show("There is no customer order with that receipt number");
        }
    }
  7. Save the file

Checking the Existence of an Item

Instead of the square brackets that allow you to retrieve a value based on its position, you can look for a value based on its complete definition. You have various options. You can first "build" an item and ask the compiler to check whether any item in the list matches your definition. To perform this search, depending on your class, you can call either the ArrayList.Contains() or the List.Contains() method. The syntax of the System.Collections.ArrayList.Contains() method is:

public virtual bool Contains(object value);

The syntax of the System.Collections.Generic.List.Contains() method is:

public bool Contains(T value);

The value to look for is passed as argument to the method. The compiler would look for exactly the value, using its definition, in the list. If any detail of the argument fails to match any value of the list, the method would return false. If all characteristics of the argument correspond to a value of the list, the method returns true. Here is an example:

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using System.Collections;

namespace Collector1
{
    public partial class Form1 : Form
    {
        ArrayList lstNames;

        public Form1()
        {
            InitializeComponent();
        }

        private void Form1_Load(object sender, EventArgs e)
        {
            lstNames = new ArrayList();

            lstNames.Add("Christine Kingston");
            lstNames.Add("Hermine Paulson");
            lstNames.Add("William Harrison");
            lstNames.Add("Ursula Morales");
            lstNames.Add("Evan Lancos");

            foreach(string str in lstNames)
                lbxNames.Items.Add(str);
        }

        private void btnResult_Click(object sender, EventArgs e)
        {
            string strFind = txtFind.Text;

            if (lstNames.Contains(strFind) == true)
                txtResult.Text = "Found";
            else
                txtResult.Text = "Not Found";
        }
    }
}
Array List
Array List

Practical Learning Practical Learning: Checking the Existence of an Item

  1. Display the Part Editor form and double-click an unoccupied area of its body
  2. Implement the Load event as follows:
     
    private void NewStoreItem_Load(object sender, EventArgs e)
    {
        // Since all values seem ready, prepare to process the item
        lstAutoParts = new List<PartDescription>();
        BinaryFormatter bfmAutoParts = new BinaryFormatter();
    
        for (int i = DateTime.Today.Year + 1; i >= 1960; i--)
            cbxYears.Items.Add(i.ToString());
    
        // Create a random number that will be used to identify the item
        Random rnd = new Random();
        txtPartNumber.Text = rnd.Next(100000, 999999).ToString();
    
        // This is the file that holds the list of parts
        string FileName = @"C:\College Park Auto Parts\Parts.prs";
    
        if (File.Exists(FileName))
        {
            FileStream stmAutoParts = new FileStream(FileName,
                                                     FileMode.Open,
                                                     FileAccess.Read,
                                                     FileShare.Read);
    
            try
            {
                // Retrieve the list of items from file
                lstAutoParts = 
    		(List<PartDescription>)
    			bfmAutoParts.Deserialize(stmAutoParts);
    
                // Display the car manufacturers in the Make combo box
                for (int i = 0; i < lstAutoParts.Count; i++)
                {
                    PartDescription part = (PartDescription)lstAutoParts[i];
    
                    if (!cbxMakes.Items.Contains(part.Make))
                        cbxMakes.Items.Add(part.Make);
                }
    
                // Display the pats categories in the Category combo box
                for (int i = 0; i < lstAutoParts.Count; i++)
                {
                    PartDescription part = (PartDescription)lstAutoParts[i];
    
                    if (!cbxCategories.Items.Contains(part.Category))
                        cbxCategories.Items.Add(part.Category);
                }
            }
            finally
            {
                stmAutoParts.Close();
            }
        }
    }
  3. Display the Central form and click the Part # text box
  4. In the Events section of the Properties window, double-click Leave and implement the event as follows:
     
    private void txtPartNumber_Leave(object sender, EventArgs e)
    {
        // We will allow the user to enter a part number
        // In the beginning, we assume that the user 
        // had entered an invalid number
        bool found = false;
        // This will represent the part found, if any
        PartDescription PartFound = null;
    
        // After the user had entered a part number,
        // check the whole list of parts
        foreach (PartDescription part in lstAutoParts)
        {
            // If you find a part that holds the number the user had entered
            if( part.PartNumber == long.Parse(txtPartNumber.Text) )
            {
                // Mark that part
                PartFound = part;
                // And update the flag that specifies that the part has been found
                found = true;
            }
            // If the part number was not found, check the next
        } // If no part has that number, the found flag keeps marked as false
    
        // If a part with that number was found...
        if (found == true)
        {
            // Show the corresponding part name and unit price
            txtPartName.Text = PartFound.PartName;
            txtUnitPrice.Text = PartFound.UnitPrice.ToString("F");
            txtQuantity.Text = "1";
            txtSubTotal.Text = PartFound.UnitPrice.ToString("F");
            // Give focus to the quantity in case the user was to increase it
            txtQuantity.Focus();
        }
        else
        {
            // Since no part with that number was found,
            // reset the text boxes
            txtPartName.Text = "";
            txtUnitPrice.Text = "0.00";
            txtQuantity.Text = "0";
            txtSubTotal.Text = "0.00";
    
            // Let the user know that the part number that 
            // was entered is not in the list
            MessageBox.Show("There is no part with that number");
        }
    }
  5. Return to the Central form and double-click the New Auto Part button
  6. Implement the event as follows:
     
    using System;
    using System.Collections.Generic;
    using System.ComponentModel;
    using System.Data;
    using System.Drawing;
    using System.Linq;
    using System.Text;
    using System.Windows.Forms;
    using System.IO;
    using System.Runtime.Serialization.Formatters.Binary;
    
    namespace CollegeParkAutoParts1
    {
        public partial class Central : Form
        {
            int iFileName;
            List<PartDescription> lstAutoParts;
    
            public Central()
            {
                InitializeComponent();
            }
    
            void ShowAutoParts()
            {
                tvwAutoParts.Nodes.Clear();
                TreeNode nodRoot =
    		tvwAutoParts.Nodes.Add("College Park Auto-Parts",
                                           "College Park Auto-Parts", 0, 1);
                // Show the years nodes
                for (int years = DateTime.Today.Year + 1; years >= 1960; years--)
                    nodRoot.Nodes.Add(years.ToString(), years.ToString(), 2, 3);
    
                tvwAutoParts.SelectedNode = nodRoot;
                // Expand the root node
                tvwAutoParts.ExpandAll();
    
                lstAutoParts = new List<PartDescription>();
                BinaryFormatter bfmAutoParts = new BinaryFormatter();
    
                // This is the file that holds the list of auto parts
                string FileName = @"C:\College Park Auto Parts\Parts.prs";
    
                if (File.Exists(FileName))
                {
                    FileStream stmAutoParts = new FileStream(FileName,
                                                             FileMode.Open,
                                                             FileAccess.Read,
                                                             FileShare.Read);
                    try
                    {
                        // Retrieve the list of parts from file
                        lstAutoParts =
    			(List<PartDescription>)
    				bfmAutoParts.Deserialize(stmAutoParts);
    
                        // Show the makes nodes
                        foreach (TreeNode nodYear in nodRoot.Nodes)
                        {
                            List<string> lstMakes = new List<string>();
    
                            foreach (PartDescription part in lstAutoParts)
                            {
                                if (nodYear.Text == part.Year.ToString())
                                {
                                    if (!lstMakes.Contains(part.Make))
                                        lstMakes.Add(part.Make);
                                }
                            }
    
                            foreach (string strMake in lstMakes)
                                nodYear.Nodes.Add(strMake, strMake, 4, 5);
                        }
    
                        // Showing the models nodes
                        foreach (TreeNode nodYear in nodRoot.Nodes)
                        {
                            foreach (TreeNode nodMake in nodYear.Nodes)
                            {
                                List<string> lstModels = new List<string>();
    
                                foreach (PartDescription part in lstAutoParts)
                                {
    
                                    if ((nodYear.Text == part.Year.ToString()) &&
                                        (nodMake.Text == part.Make))
                                    {
                                        if (!lstModels.Contains(part.Model))
                                            lstModels.Add(part.Model);
    
                                    }
                                }
    
                                foreach (string strModel in lstModels)
                                    nodMake.Nodes.Add(strModel, strModel, 6, 7);
                            }
                        }
    
                        // Showing the categories nodes
                        foreach (TreeNode nodYear in nodRoot.Nodes)
                        {
                            foreach (TreeNode nodMake in nodYear.Nodes)
                            {
                                foreach (TreeNode nodModel in nodMake.Nodes)
                                {
                                    List<string> lstCategories = new List<string>();
    
                                    foreach (PartDescription part in lstAutoParts)
                                    {
    
                                        if ((nodYear.Text == part.Year.ToString()) &&
                                            (nodMake.Text == part.Make) &&
                                            (nodModel.Text == part.Model))
                                        {
                                            if (!lstCategories.Contains(part.Category))
                                                lstCategories.Add(part.Category);
                                        }
                                    }
    
                                    foreach (string strCategory in lstCategories)
                                        nodModel.Nodes.Add(strCategory,
    						       strCategory, 8, 9);
                                }
                            }
                        }
                    }
                    finally
                    {
                        stmAutoParts.Close();
                    }
                }
            }
    
    	. . . No Change
    
            private void btnNewAutoPart_Click(object sender, EventArgs e)
            {
                var editor = new NewStoreItem();
    
                if (editor.ShowDialog() == DialogResult.Cancel)
                    ShowAutoParts();
            }
        }
    }
  7. Display the Central form and double- click the New Customer Order button
  8. Implement the event as follows:
     
    private void btnNewCustomerOrder_Click(object sender, EventArgs e)
    {
        // We will store our files in the following folder    
        string strDirectory = @"C:\College Park Auto Parts\Receipts";
        DirectoryInfo dirInfo = Directory.CreateDirectory(strDirectory);
    
        // Get the list of files, if any, from our directory
        FileInfo[] fleList = dirInfo.GetFiles();
    
        // If there is no file in the directory,
        // then we will use 1000 as the first file name
        if (fleList.Length == 0)
        {
            iFileName = 1000;
        }
        else // If there was at least one file in the directory
        {
            // Get a reference to the last file
            FileInfo fleLast = fleList[fleList.Length - 1];
            // Get the name of the last file without its extension
            string fwe = Path.GetFileNameWithoutExtension(fleLast.FullName);
            // Increment the name of the file by 1
            iFileName = int.Parse(fwe) + 1;
        }
    
        txtSave.Text = iFileName.ToString();
    
        lvwAutoParts.Items.Clear();
        lvwSelectedParts.Items.Clear();
    }
  9. Display the Central form and double-click an unoccupied area of its body
  10. Define a new method and implement the Load event as follows:
     
    private void Central_Load(object sender, EventArgs e)
    {
        ShowAutoParts();
        btnNewCustomerOrder_Click(sender, e);
    }
  11. Return to the Central form and click the tree view
  12. In the Properties window, click the Events button and, in the Events section, double-click NodeMouseClick
  13. Implement the event as follows:
     
    private void tvwAutoParts_NodeMouseClick(object sender,
    			TreeNodeMouseClickEventArgs e)
    {
        TreeNode nodClicked = e.Node;
    
        if (nodClicked.Level == 4)
            lvwAutoParts.Items.Clear();
    
        try
        {
            foreach (PartDescription part in lstAutoParts)
            {
                if ((part.Category == nodClicked.Text) &&
                    (part.Model == nodClicked.Parent.Text) &&
                    (part.Make == nodClicked.Parent.Parent.Text) &&
                    (part.Year.ToString() == nodClicked.Parent.Parent.Parent.Text))
                {
                    ListViewItem lviAutoPart =
    			new ListViewItem(part.PartNumber.ToString());
    
                    lviAutoPart.SubItems.Add(part.PartName);
                    lviAutoPart.SubItems.Add(part.UnitPrice.ToString("F"));
                    lvwAutoParts.Items.Add(lviAutoPart);
                }
            }
        }
        catch (NullReferenceException)
        {
        }
    }
  14. Return to the Central form and double-click the Close button
  15. Implement the event as follows:
     
    private void btnClose_Click(object sender, EventArgs e)
    {
        Close();
    }
  16. Execute the application
  17. Click the New Auto Part button and use the Part Editor to create a few parts (let the computer generate the part numbers)
     
  18. Close the Part Editor
  19. Create a few customer part orders and save them:
     
    College Park Auto Parts: Customer Order
     
    College Park Auto Parts: Part Selection
  20. Close the forms and return to your programming environment
  21. Execute the application again and open a previously saved order
  22. Close the forms and return to your programming environment

Searching for an Item

Another option to look for an item in a list consists of calling the BinarySearch() method of either the ArrayList or the List class. It is overloaded in three versions and one of them uses the following syntax:

public virtual int BinarySearch(object value);
public int BinarySearch(T value);

The value to look for is passed argument to the method. Here is an example:

private void btnResult_Click(object sender, EventArgs e)
{
    string strFind = txtFind.Text;

    if( lstNames.BinarySearch(strFind) > 0 )
        txtResult.Text = "Found";
    else
        txtResult.Text = "Not Found";
}
 

Clearing a List

To remove all items from a list at once, you can call the Clear() method of either the ArrayList or the List class. Its syntax is:

public virtual void Clear()

Deleting an Item

As opposed to adding a value to a list, you may want to remove one. To perform this operation, you have various options. You can ask the compiler to look for an item in the list and if, or once, the compiler finds it, it would delete the value. To perform this type of deletion, you can call the Remove() method of either the ArrayList or the List class. Its syntax is:

public virtual void Remove(object value);
public bool Remove(T value);

This method accepts as argument the value that you want to delete from the list. To perform this operation, the list must not be read-only.

The Remove() method allows you to specify the exact value you want to delete from a list. Another option you have consists of deleting a value based on its position. This is done using the RemoveAt() method whose syntax is:

public virtual void RemoveAt(int index);
public void RemoveAt(int index);

With this method, the position of the item is passed as argument. Here is an example:

private void btnSecond_Click(object sender, EventArgs e)
{
    lstNames.RemoveAt(1);
    lbxNames.Items.Clear();

    foreach (string str in lstNames)
        lbxNames.Items.Add(str);
}

If the position is not valid because either it is lower or higher than the current Count, the compiler would throw an ArgumentOutOfRangeException exception.

Exercises

 

Musical Instrument Store

  1. Create a Windows Application named MusicInstrumentStore3
  2. Follow the instructions from the previous lesson to design the forms
  3. Use the ArrayList class to create and manage the list of store items
  4. Configure the application so that, if the user double-clicks an object in the Available Items list view:
    1. The Item Editor would open and display the information about the item that was clicked
    2. The Create button would display a caption as Submit
    3. The Close button would display a caption as Cancel
    4. The user can then change any detail about the item and click
    5. If the user clicks Submit, the (same) item would be updated in the database
    6. If the user clicks Cancel, the dialog box would be closed and the item would not receive any change
  5. Configure the Available Items list view so that, if the user clicks an item and presses Delete:
    1. A message box would ask the user, "Are you sure you want to remove this item from the database?" and would display two buttons: Yes and No
    2. If the user clicks Yes, the item would be removed from the database
    3. If the user clicks No, nothing would happen

College Park Auto Parts

 
  1. Open the CollegeParkAutoParts1 application from this lesson
  2. Add a context menu for the Available Parts list view with the items: Select, Edit..., and Delete
     
  3. Configure the context menu so that
    1. If the user clicks Select, the behavior would be the same as if the user had double-clicked the item
    2. If the user clicks Edit..., the Part Editor dialog box would display with the part in it. The user can then edit any part (year, make, model, category, part name, or unit price) except the part number. Then the user can save the changed part
    3. If the user clicks Delete, a message box would warn the user and ask for confirmation with Yes/No answers. If the user clicks Yes, the part would be deleted from the list of auto parts
  4. Configure the application so that the user can open an order, add new parts to it, or delete parts from it, then save the order
  5. Extend the application so that the store can also sell items that are, or are not, car-related, such as books, t-shirts, cleaning items, maintenance items (steering oils, brake oils, etc), license plates, etc. Every item in the store should have an item number. The user can enter that item number in the Part # text box and press Tab or Enter. The corresponding item would then be retrieved from the database and displayed on the form. If there is no item with that number, a message box should let the user know

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