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Objects Fundamentals

 

Introduction

An object is anything that can be described. In the real world, examples of objects are the moon, a ball, a hand, a book, a head, a song, a box. As different as objects are, they follow some basic rules used to describe them. A characteristic of an object is a word or a group of words used to describe the object. Some characteristics are applied to all objects. For example, every object must be identified with a word or a group of words referred to as its Name:

 
Object Person Table Ball Insect Map
Name Person Table Ball Insect Map

Some characteristics apply to a group of objects but don't apply to another group. For example, a characteristic called width can be used to describe a car, a medical pill, a piece of paper, or a computer monitor:

Common Characteristics Digital Camera Clothes Basket Car Tennis Ball
Name Digital Camera Basket Car Tennis Ball
External Color Black Blue Grey Yellow
Unit Price 899.95 24.55 19995.00 6.25

Some other characteristics can be applied to one object or one type of object that is mostly unique.

When creating a database, you will also use objects but these are referred to as Windows controls or simply controls. In a typical application, you will choose the objects, that is, the controls that you judge necessary and you will make them part of your application. Here is an example of a form with various controls:

Bethesda Car Rental - Order Processing

As we move, we will indicate how to choose controls and populate a form with them.

 

Practical LearningPractical Learning: Introducing Objects

  1. Start Microsoft Access and, from the resources that accompany these lessons, open the Exercise1 database
  2. To display an existing object, under the Objects bar of the Database window, click Forms
  3. In the right frame of the window, double-click Sample Form
     
 

The Properties of an Object

In the programming world, a characteristic of an object is referred to as a property of that object. For example, as mentioned above, every object must have a name. The name is used to identify the object. In the same way, the other characteristics that we reviewed above are in fact the properties of that object.

Because every object has properties, they can be created as a list. Consider the second table we saw above:

Common Characteristics Digital Camera Clothes Basket Car Tennis Ball
Name Digital Camera Basket Car Tennis Ball
External Color Black Blue Grey Yellow
Unit Price 899.95 24.55 19995.00 6.25

The properties of each object are: its name, its external color, and its unit price. This can be illustrated as:

Object
Property Name
Name
External Color
Unit Price

To represent an object, that is, to describe it, you can give a value to each property. For example, the properties of the digital camera from the above table are its Name, its External Color, and its Unit Price. The values of the properties of that camera are: Name: Digital Camera, External Color: Black, Unit Price: 899.95. This can be illustrated as:

Object
Property Name Property Value
Name Digital Camera
External Color Black
Unit Price 899.95

From this illustration, it is important to make a distinction between a property and its value: a property is a word or a group of words used to define what constitutes an object. A value is the word or a group of words used to formally describe an object. In the programming world, the name of a property is always of one word only, as the Name property in the above table. If a name is made of more than one word, then they must be combined into one. In the same way, the value of a property is made of only one word. Also, if the name is a combination of words, they must be concatenated (added) to produce one word. Based on this, the properties and their values from the above table would be:

Object
Name DigitalCamera
ExternalColor Black
UnitPrice 899.95

Just as done in the real world, Microsoft Access also relies on objects to represent a database. One of the most regularly used objects of a database is called a table. Another regularly used object of an application is called a form. There are many other objects as we will find out in future lessons.

Visually Accessing the Properties of an Object

Each object has properties. To effectively use an object, you should be familiar with its properties or at least how to use them to describe an object.

During the design of an object, you will have a window that represents its properties. The window that displays the list of properties is different depending on the object and depending on whether you are working in Microsoft Access or in Microsoft Visual Basic. For a form, which is probably the most regularly used object of an application, in these lessons, the window that presents its properties will be called the Properties window. It appears as a resizable horizontal window with 5 tabs labeled Format, Data, Event, Other, and All:

As mentioned in the previous lesson, in Microsoft Visual Basic, the Properties window usually appears in the lower left section of the screen and appears with 2 tabs labeled Alphabetic and Categorized:

To visually configure a property, you must first locate it in the Properties window. If you are working in Microsoft Access, the properties are categorized in three tabs: Format, Data, and Other. All of these properties are also represented in the All tab. Each property appears with its name as in the real world: in different words. Examples are Caption, Default View, or Min Max Buttons. After locating the property, to see or change its value, you use the box on its right. This means that a property is made of two sections: a property name and a property value. This can be illustrated as follows:

If you are working in Microsoft Visual Basic, you can use the same approach to change a property using the Properties window. This time, the names of properties appear in one word and they are in their official format.

 

Programmatically Accessing the Properties of an Object

To programmatically change a property, in your code section, type the name of its object, followed by a period operator ".", followed by the official name of the property, followed by the assignment operator, and followed by the desired value. This means that you must know the name of the object whose property you want to change. You must know the name of the property you want to change, and you must know the possible values that the property can receive. Here is an example of code that hides a rectangular box, named boxRectangle, when the user clicks a button:

Private Sub cmdHide_Click()
    boxRectangle.Visible = False
End Sub

Fortunately, when writing code, the Code Editor is equipped to assist you with the names of available properties. When you type the name of a object followed by the period operator, the available properties would appear in a list:

We mentioned earlier that the names of objects are usually in one word. In reality, Microsoft Access is very flexible and allows you to use more than one word to name an object (but the properties names are always in one word). If you have an object that is made of more than one word, when referring to it in an expression, whether in the Properties window or with your code, you must include it between the opening square bracket "[" and the closing square bracket "]". For example, suppose that you have a box named Rectangular Box instead of boxRectangle. The above code would be written as:

Private Sub cmdHide_Click()
    [Rectangular Box].Visible = False
End Sub

There is no penalty if you always include the name of an object in square brackets when referring to it whether in the Properties window or with code, even if the name is made of one word. Here is an example:

Private Sub cmdHide_Click()
    [boxRectangle].Visible = False
End Sub

This would produce the same result as above.

Practical LearningPractical Learning: Introducing Properties

  1. To change the view of the form, while the form is activated, on the main menu, click View -> Design View
  2. Notice that a window appears with a caption that displays Form. If you don't see it, on the main menu of Microsoft Access, click View -> Properties
     
  3. This is the Properties window in Microsoft Access. Notice that it is divided in five property pages
  4. To open Microsoft Visual Basic, on the Standard toolbar of Microsoft Access, click the Code button Code
  5. Notice that the Properties window displays the properties of the form as it is selected in the Project window
  6. In the Object combo box of the Code Editor, select Form
  7. Type NavigationButtons = False
     
  8. To return to Microsoft Access, on the toolbar, click the View Microsoft Access button View Microsoft Access
  9. On the Standard toolbar of Microsoft Access, click the View button Button: Form View
     
  10. After viewing the result, on the Form View toolbar of Microsoft Access, click the View button Design View

With the Properties of an Object

Sometimes, you will need to access only one property of an object. In some other cases, you will need to change various properties to perform a specific task. To do this for each property, as we saw above, you can type the name of the object, followed by the period operator, followed by the name of the property, press Enter, and do the same on the next line. Here is an example:

Private Sub cmdManipulate_Click()
    boxEnvelop.BackStyle     = 1
    boxEnvelop.BackColor     = 979478
    boxEnvelop.SpecialEffect = 1
    boxEnvelop.BorderColor   = 234657
    boxEnvelop.BorderWidth   = 2
End Sub

As an alternative, instead of typing the name of the control over and over again, you can use the With operator whose formula is:

With ObjectName
	Statements
End With

On the right side of the With keyword, type the name of the control whose properties you want to access. Under the With ObjectName line, type your statements and expressions as you wish but start each property of the ObjectName with the period operator ".". At the end of the With statement, type End With. Based on this, the above code would have been written:

Private Sub cmdManipulate_Click()
    With boxEnvelop
    	.BackStyle     = 1
    	.BackColor     = 979478
    	.SpecialEffect = 1
    	.BorderColor   = 234657
    	.BorderWidth   = 2
    End With
End Sub
 
 

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