User Controls

User Controls are the controls which are created by the user and they are based on the class System.Windows.Forms.UserControl. Like standard controls, user controls support properties, methods and events. Once a user control is created it can be added to any form or any number of forms like all other controls.

Creating a User Control

To create a user control select File->New->Project->Visual Basic Projects and select Windows Control Library from the templates and click OK. Alternatively, you can add user control to the existing project by selecting Project->Add User Control. The image below displays the new project dialogue to add a User Control project.

The form that opens after clicking OK looks like the image below. It looks similar to a normal form.

Creating  a User Control with Example

Drag a Label and a TextBox control from the toolbox onto the new user control form. The image below displays that.

Double-click the user control form to open it's code behind file. In the code behind file type the following code below the Load event (under End Sub) of UserControl1 to set the property of the user control which is being created.

 

Public Property sanText() As String Get sanText = TextBox1.Text End Get Set(ByVal Value As String) TextBox1.Text = Value End Set End Property Public Property sanLbl() As String Get sanLbl = Label1.Text End Get Set(ByVal Value As String) Label1.Text = Value End Set End Property

The above code implements the sanText() and sanLbl() properties with a property get/set pair. Once typing the code is done build the solution using Build->Build Solution from the main menu to create the .dll (Dynamic Link Library) file to which we refer to. The dll file also makes this user control available to other projects. After finishing building the solution we next need to add this user control to the toolbox to make it available to other projects and forms. To do that, open a windows form or use an existing form. Right-click on the Windows Form tab section on the toolbox and click on Customize Toolbox as shown in the image below.

Clicking on Customize Toolbox opens "Customize Toolbox" dialogue box as shown in the image below.

On this window select the .NET Framework components tab which displays a list. Click browse to add the dll of the user control we created and select the dll file from the bin directory of the Windows Control library project. Once that is done, click OK. The dll of the user control gets added to the .NET Framework Components. Select that and click OK. The user control which we created gets added to the toolbox. Now this control can be used like other controls in the toolbox.

Alternatively, the user control can be added to the toolbox in another way. To do that, right-click on the References item in the Solution Explorer window and select Add Reference which opens the Add Reference dialogue box. Select the projects tab and double-click the User Control item. That adds item to the selected components box at the bottom of the dialog. click OK to finish.

Using the User Control

The user control, UserControl11 which we created can be added to any form like all other controls. Open a new form and drag this user control from toolbox to the form. Drag a Button from the toolbox and place that on the form. Double-click Button to open it's Click event. Place the following code in the Click event of the Button:

Private Sub Button1_Click(ByVal sender As System.Object, ByVal_ e As System.EventArgs) Handles Button1.Click MessageBox.Show("TextBox" & UserControl11.sanText()) MessageBox.Show("Label1" & UserControl11.sanLbl()) End Sub

Run the code and enter some text in the TextBox. When you click the Button, the text entered in the TextBox is displayed in a MessageBox. That's the way User Controls are used after they are created.

Inherting Controls

One of the easiest ways to create a new control is to inherit from a preexisting control. When inheriting from an existing control, the newly created control contains all the functionality of the base control but can also serve as a base for adding new functionality. In addition to having all the functionality of the base control an inherited control also inherits the visual representation of the base control. For example, you can inherit from a TextBox control and implement code to change its appearance.

Unless sealed (NotInheritable), most Windows Controls can be used as a base class for inheritance. Inheriting from an existing control is the most easiest way of creating a new control. You can choose this method if you want to replicate an exisiting windows control and want to add more functionality to it. You can also use this method if you want to have all the functionality of the existing control but want to provide a new look and feel.

To create a new Inherited control you must specify a Windows Form control as a base class for this control. The following sample code creates a textbox that accepts only numbers as user input.To implement that functionality you must override the OnKeyPress method as shown below.

Public Class NumberOnlyBox Inherits System.Windows.Forms.TextBox Protected Overrides Sub OnKeyPress(ByVal e as KeyPressEventArgs) If Char.IsNumber(e.KeyChar)=False Then e.handled=True End If End Sub End Class