The Register control performs the following tasks that are common to all composite controls:
The CompositeControl class implements the common functionality needed by all composite controls. It also has an associated control designer that ensures that child controls are displayed on the design surface in a visual designer.
.gif) Note: |
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The
CompositeControl class is new in ASP.NET 2.0. If you created custom controls in ASP.NET version 1.0 or 1.1, you had to implement the INamingContainer interface to create a new naming scope for child controls. In addition, you had to override the Controls property and invoke the EnsureChildControls method. In ASP.NET 2.0, these and other steps are performed by the CompositeControl class.
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You should create the child controls in the CreateChildControls method and not in OnInit or another life cycle phase. The server control architecture relies on calls to CreateChildControls whenever the Controls collection is needed, such as during data binding (if applicable).
The Register control also illustrates how to expose properties of child controls as top-level properties. This is useful when you want to allow the page developer to access the properties of a child control. For example, Register exposes the Text property of the Button child control as its own ButtonText property, as shown in the following code drawn from the example:
< _
Bindable(True), _
Category("Appearance"), _
DefaultValue(""), _
Description("The text to display on the button.") _
> _
Public Property ButtonText() As String
Get
EnsureChildControls()
Return submitButton.Text
End Get
Set(ByVal value As String)
EnsureChildControls()
submitButton.Text = value
End Set
End Property
[
Bindable(true),
Category("Appearance"),
DefaultValue(""),
Description("The text to display on the button.")
]
public string ButtonText
{
get
{
EnsureChildControls();
return submitButton.Text;
}
set
{
EnsureChildControls();
submitButton.Text = value;
}
}
The Register control does not store ButtonText or other properties it delegates to child controls in view state because the child controls use view state for storing these properties. For information on how to manage the state of properties that are not delegated to child controls, see Server Control Properties Example. That topic contains information about using the ViewState dictionary for storing simple properties and implementing custom state management for properties that have subproperties.
The Register control shows how to raise an event from the handler of a child control's event. The Register control defines an event named Submit and raises the event by attaching a handler to the Click event of the Button child control.