Composite Control vs. User Control
The following table summarizes the differences between composite controls and user controls. For details about authoring a user control, see Web Forms User Controls.
|Composite Control||User Control|
|Minimal design-time support for authoring.||Full design-time support for authoring. Authoring a user control in a visual designer is no different from authoring an ASP.NET page (Web Forms page).|
|Authored programmatically in an object-oriented programming language that targets the common language runtime, such as C# or Visual Basic .NET.||Authored declaratively using ASP.NET page syntax and script blocks (or code-behind pages).
|Compiled and persisted as an assembly (.dll).||Saved as a text file with an .ascx extension (with an optional code-behind file).|
|Well suited to authoring generic redistributable controls.||Geared toward application-specific functionality.|
|Full design-time support when used in a design-time host. A composite control can be added to the toolbox of a visual designer and dragged and dropped onto a page.||Minimal support for use in a designer.|
Note If you want to extend the functionality of a single control, for instance Label, do not create a composite control or a user control. In that case, you should derive from Label (to get the benefits of inheritance and polymorphism) and add or override members. If you create a user control (or composite control) that contains only one control, Label, your new control no longer has the object model of Label. You should create a user control (or a composite control) only when you want to combine multiple existing controls.
The following sample shows a user control that is equivalent to the composite control developed in the Composite Server Control Sample. The user control raises a custom event named
Check. The event delegate
CheckEventHandler and the event data class
CheckEventArgs, which are used by the
Check event, are defined in the Composite Server Control Sample.
<%-- UserControl.ascx. --%> <%-- The namespace CustomControls has to be imported because it contains CheckEventArgs and CheckEventHandler. --%> <%@Import Namespace = "CustomControls" %> <script language="VB" runat=server> Private ReadOnly Property Sum() As Integer Get EnsureChildControls() Return Int32.Parse(box1.Text) + Int32.Parse(box2.Text) End Get End Property Public Number As Integer = 100 Public Property Text() As String Get EnsureChildControls() Return label.Text End Get Set EnsureChildControls() label.Text = value End Set End Property Public Event Check As CheckEventHandler Protected Overridable Sub OnCheck(e As CheckEventArgs) RaiseEvent Check(Me, e) End Sub Private Sub Button_Clicked(sender As Object, e As EventArgs) OnCheck(New CheckEventArgs(Sum - Number)) End Sub </script> <h3>Enter a number : <asp:TextBox id = box1 text = "0" runat = server /> </h3> <br> <h3>Enter another number : <asp:TextBox id = box2 text = "0" runat = server /> </h3> <br> <asp:Button id = button text = "Submit" OnClick = "Button_Clicked" runat = server /> <br> <br> <asp:Label id = label text = "Click sumbit to see if you won." height = 100 width = 400 runat = server />
Using a User Control on a Page
The following page uses the user control
UserControl.ascx on an ASP.NET page. For more details, see Including a User Control in a Web Forms Page.
<%@Import Namespace = "CustomControls" %> <%@ Register TagPrefix="MyUserControl" TagName = "MyControl" Src = "UserControl.ascx" %> <script language="VB" runat=server> Private Sub Sum_Checked(sender As Object, e As CheckEventArgs) If e.Match = True Then control.Text = "<h2> You won a million dollars!!!! </h2>" Else control.Text = "Sorry, try again. The numbers you entered don't add up to" & _ " the hidden number." End If End Sub </script> <html> <body> <h1> The mystery sum game </h1><br> <form runat=server> <MyUserControl:MyControl id = "control" OnCheck = "Sum_Checked" Number = "10" runat = server/> </form> </body> </html>