Alternatively, to add a control, you can also double-click it from the Toolbox and it would be added to the top-left section of the form.
If you want to add a certain control many times, before selecting it on the Toolbox, press and hold Ctrl. Then click it in the Toolbox. This permanently selects the control. Every time you click the form, the control would be added. Once you have added the desired number of this control, on the Toolbox, click the Pointer button to dismiss the control.
We mentioned earlier how you could add a control many times. An alternative is to copy a control. To do this, on the form:
You can use these two techniques to copy a group of controls.
The objects used in a Windows application are defined in various assemblies. To add one of these controls to your application, you must first know the name of its class. With this information, you can declare a variable of its class. For example, a command button is an object of type Button that is based on the Button class. The Button class is defined in the System.Windows.Forms namespace of the System.Windows.Forms.dll assembly. Based on this, to create a button, you can create a variable of type Button. Here is an example:
Imports System Imports System.Windows.Forms Module Exercise Public Class Exercise Inherits Form Private BtnSubmit As Button Public Sub New() End Sub Public Shared Function Main() As Integer Application.Run(New Exercise()) Return 0 End Function End Class End Module
After declaring the variable, you can use the New operator to allocate memory for it:
Public Sub New() BtnSubmit = New Button() End Sub
This is also referred to as dynamically creating a control. After declaring the variable and allocating memory for it, the control is available but does not have a host, which makes it invisible. A control must be positioned on a container, like a form. The Form class itself contains a member variable named Controls. This member holds a list of the objects that are placed on the form. To specify that a control you have instantiated must be positioned on a form, the Controls member has a method named Add. Therefore, to make an object part of the form, pass its variable to the Add() method. Here is an example:
Imports System Imports System.Windows.Forms Module Exercise Public Class Exercise Inherits Form Private BtnSubmit As Button Public Sub New() BtnSubmit = New Button() Controls.Add(BtnSubmit) End Sub Public Shared Function Main() As Integer Application.Run(New Exercise()) Return 0 End Function End Class End Module
This makes it possible for the control to appear on the form when the form displays to the user:
The two techniques of visual addition of objects and dynamic creation are the most used to add Windows controls to an application. The Windows controls are also called components.
Because there can be many controls used in a program, instead of using the constructor to initialize them, the Visual Studio standards recommend that you create a sub procedure called InitializeComponent to initialize the various objects used in your application. Then simply call that method from the constructor of your form. This would be done as follows:
Imports System Imports System.Windows.Forms Module Exercise Public Class Exercise Inherits Form Private BtnSubmit As Button Public Sub New() InitializeComponent() End Sub Public Sub InitializeComponent() BtnSubmit = New Button() Controls.Add(BtnSubmit) End Sub Public Shared Function Main() As Integer Application.Run(New Exercise()) Return 0 End Function End Class End Module
Notice that the control is created in the InitializeComponent() method.
Starting in Microsoft Visual Basic 2005, and probably getting close to C++, you can use two files to create and use a form. Each file would hold a partial definition of the class. As done in a header file of a C++ application, the first file in VBasic would hold the variable or control declarations. While in C++ a header file holds the same name (but different extensions) as its corresponding source file, because VBasic does not have the concepts of header and source file, each file must have a different name. In Microsoft Visual Basic, the name of the first file of a form starts with the name of the form, followed by a period, followed by Designer, followed by a period, and followed by the vb extension.
As you add and remove components on an application, you need a way to count them to keep track of what components, and how many of them, your application is using. To assist you with this, the .NET Framework provides a class named Container. This class is defined in the ComponentModel namespace that is itself part of the System namespace. To use a variable of this class in your application, declare a variable of type Container. Because no other part of the application is interested in this variable, you should declare it private. This can be done as follows:
Imports System Imports System.Windows.Forms Module Exercise Public Class Exercise Partial Public Class Exercise Inherits Form Private BtnSubmit As Button Dim components As System.ComponentModel.Container Public Sub New() InitializeComponent() End Sub Public Sub InitializeComponent() BtnSubmit = New Button() Controls.Add(BtnSubmit) End Sub End Class Public Shared Function Main() As Integer Application.Run(New Exercise()) Return 0 End Function End Class End Module
After this declaration, the compiler can keep track of the components that are part of the form.
If you are using a .NET Framework control, you must know the name of the class on which the control is based (and each control is based on a particular class). If you have examined the types of classes available but none implements the behavior you need, you can first locate one that is close to the behavior you are looking for, then use it as a base to derive a new class.
To derive a class from an existing control, you can use your knowledge of inheritance. Here is an example:
Public Class Numeric Inherits System.Windows.Forms.TextBox End Class
If you want to perform some early initialization to customize your new control, you can declare a constructor. Here is an example:
Public Class Numeric Inherits System.Windows.Forms.TextBox Public Sub New() End Sub End Class
Besides the constructor, in your class, you can add the fields and methods as you see fit. You can also use it to globally set a value for a variable of the parent class. Once the control is ready, you can dynamically use it like any other control. Here is an example:
Imports System Imports System.Windows.Forms Module Exercise Public Class Numeric Inherits System.Windows.Forms.TextBox Public Sub New() End Sub End Class Public Class Exercise Partial Public Class Exercise Inherits Form Private BtnSubmit As Numeric Dim components As System.ComponentModel.Container Public Sub New() InitializeComponent() End Sub Public Sub InitializeComponent() BtnSubmit = New Numeric() Controls.Add(BtnSubmit) End Sub End Class Public Shared Function Main() As Integer Application.Run(New Exercise()) Return 0 End Function End Class End Module
When designing an application, you will manipulate the windows controls on a form. After adding a control to a form, before performing any operation on that control, you must first select it. You can also manipulate many controls at the same time. To do that, you will have to select all those controls.
To select one control on the form, you can simply click it. A control that is selected indicates this by displaying 8 small squares, also called handles, around it. Between these handles, the control is surrounded by dotted rectangles. In the following picture, the selected rectangle displays 8 small squares around its shape:
After selecting a control, you can manipulate it or change its characteristics, also called properties.
To select more than one control on the form, click the first. Press and hold either Shift or Ctrl. Then click each of the desired controls on the form. If you click a control that should not be selected, click it again. After selecting the group of controls, release either Shift or Ctrl that you were holding.
When a group of controls is selected, the last selected control displays 8 square handles around but its handles are white while the others are black. Another technique you can use to select various controls consists of clicking on an unoccupied area on the form, holding the mouse down, drawing a fake rectangle, and releasing the mouse:
Every control touched by the fake rectangle or included in it would be selected:
If there is a control on your form but you don't need it, you can remove it from the application. To delete a control, first select it and then click or press Delete. You can also right-click a control and click Cut. To remove a group of controls, first select them, then click or press Delete or right-click the selection and click Cut.
A property is a piece of information that characterizes or describes a control. It could be related to its location or size. It could be its color, its identification, or any visual aspect that gives it meaning. The properties of an object can be changed either at design time or at run time. You can also manipulate these characteristics both at design and at run times. This means that you can set some properties at design time and some others at run time.
To manipulate the properties of a control at design time, first select it on the form. While a control is selected, use the Properties window to manipulate the properties of the control at design time. To access the Properties window if it is not visible:
The Properties window uses the behaviors we reviewed in Lesson 1 about auto-hiding, docking, floating or tabbing the tools that accompany Microsoft Visual Studio 2005. This means that you can position it on one side of the screen or to have it float on the screen as you wish.
The Properties window is divided in 5 sections:
The Properties window starts on top with a title bar, which displays the string Properties. If the window is docked somewhere, it displays the Window Position , the Auto-Hide , and the Close buttons on its right side. If the window is floating, it would display only the Close button.
Under the title bar, the Properties window displays a combo box. The content of the combo box is the name of the form plus the names of the controls currently on the form. Besides the technique we reviewed earlier to select a control, you can click the arrow of the combo box and select a control from the list:
Under the combo box, the Properties displays a toolbar with 4 buttons.
Under the toolbar, the Properties window displays the list of properties of the selected control(s). On the right side, the list is equipped with a vertical scroll bar. The items in the Properties window display in a list set when installing Microsoft Visual Studio. In the beginning, you may be regularly lost when looking for a particular property because the list is not arranged in a strict order of rules. You can rearrange the list. For example, you can cause the items to display in alphabetic order. To do this, on the toolbar of the Properties window, click the Alphabetic button . To restore the list, you can click the categorized button .
Two lists share the main area of the Properties window. When the list of properties is displaying, the Properties button is clicked . The second is the list of events. Therefore, to show the events, you can click the Events button . If the events section is displaying, to show the list of properties, you can click the Properties button .
Under the list of properties, there is a long bar that displays some messages. The area is actually a help section that displays a short description of the property that is selected in the main area of the Properties window.
Based on a previous description,
When a control is selected, the Properties window displays only its characteristics:
You can also change some characteristics of various controls at the same time. To do this, first select the controls on the form and access the Properties window:
When various controls have been selected:
Each field in the Properties window has two sections:
the propertyï¿½s name and the property's value:
The name of a property is represented on the left column. This is the official name of the property. The names of properties are in one word. You can use this same name to access the property in code.
The box on the right side of each property name represents the value of the property that you can set for an object. There are various kinds of fields you will use to set the properties. To know what particular kind a field is, you can click its name. To set or change a property, you use the box on the right side of the property's name: the property's value, also referred to as the field's value.
There are fields that expect you to type a value. Most of these fields have a default value. Here is an example:
To change the value of the property, click the name of the property, type the desired value, and press Enter.
While some properties, such as the Text, would allow anything, some other fields expect a specific type of text, such as a numeric value.
Some fields expect a numeric value. In this case, you can click the name of the field and type the desired value. Here is an example:
If you type an invalid value, you would receive a message box notifying you of the error:
When this happens, click OK and type a valid value. If the value is supposed to be an integer, make sure you don't type it as a decimal number.
Some fields expect you to enter a date. You must type a valid date recognized by the operating system and the Regional and Language Settings in Control Panel. If you enter an invalid date, you would receive an error.
To collapse the field, click the - button.
Some of the properties are numeric based, such as the Location or the Size. With such a property, you can click its name and type two numeric values separated by a comma. Some other properties are created from an enumeration or a class. If you expand such a field, it would display various options. Here is an example from the Font property:
With such a property, you should select from a list.
To change the value of some of the fields, you would use their combo box to display the available values. After clicking the arrow, a list would display:
There are various types of list-based fields. Some of them display just two items. To change their value, you can just double-click the field. Some other fields have more than two values in the field. To change them, you can click their arrow and select from the list. You can also double-click a few times until the desired value is selected.
Some properties provide a window from where you can select the desired option. The field primarily displays the arrow of a combo box. To use the field, you click the arrow of the combo box and the window appears. Here are examples:
After expanding the window, you can select the desired option. We will eventually review them.