IExtenderProvider Interface
Assembly: System (in system.dll)
An extender provider is a component that provides properties to other components. For example, the ToolTip control is an extender provider. When you add a ToolTip control to a Form, all other controls on the form have a ToolTip property added to their list of properties.
Any component that provides extender properties must implement IExtenderProvider. A visual designer can then call CanExtend to determine which objects in a container should receive the extender properties.
For more information about extender providers, see How to: Implement an Extender Provider.
The following code example demonstrates how to implement the IExtenderProvider interface. This example is part of a larger example discussed in How to: Implement a HelpLabel Extender Provider.
Option Strict On Option Explicit On Imports System Imports System.Collections Imports System.ComponentModel Imports System.ComponentModel.Design Imports System.Drawing Imports System.Windows.Forms Imports System.Windows.Forms.Design Namespace Microsoft.Samples.WinForms.Vb.HelpLabel ' ' <doc> ' <desc> ' Help Label offers an extender property called ' HelpText. It monitors the active control ' and displays the help text for the active control. ' </desc> ' </doc> ' <ProvideProperty("HelpText", GetType(Control)), Designer(GetType(HelpLabel.HelpLabelDesigner))> _ Public Class HelpLabel Inherits Control Implements System.ComponentModel.IExtenderProvider ' <summary> ' Required designer variable. ' </summary> Private components As System.ComponentModel.Container Private helpTexts As Hashtable Private activeControl As System.Windows.Forms.Control ' ' <doc> ' <desc> ' Creates a new help label object. ' </desc> ' </doc> ' Public Sub New() ' ' Required for Windows Form designer support. ' InitializeComponent() helpTexts = New Hashtable End Sub ' <summary> ' Clean up any resources being used. ' </summary> Protected Overloads Overrides Sub Dispose(ByVal disposing As Boolean) If disposing Then If components IsNot Nothing Then components.Dispose() End If End If MyBase.Dispose(disposing) End Sub ' <summary> ' Required method for designer support. Do not modify ' the contents of this method with the code editor. ' </summary> Private Sub InitializeComponent() Me.components = New System.ComponentModel.Container Me.BackColor = System.Drawing.SystemColors.Info Me.ForeColor = System.Drawing.SystemColors.InfoText Me.TabStop = False End Sub ' ' <doc> ' <desc> ' Overrides the text property of Control. This label ignores ' the text property, so we add additional attributes here so the ' property does not show up in the Properties window and is not ' persisted. ' </desc> ' </doc> ' <Browsable(False), _ EditorBrowsable(EditorBrowsableState.Never), _ DesignerSerializationVisibility(DesignerSerializationVisibility.Hidden)> _ Public Overrides Property [Text]() As String Get Return MyBase.Text End Get Set(ByVal Value As String) MyBase.Text = Value End Set End Property ' ' <doc> ' <desc> ' This implements the IExtenderProvider.CanExtend method. The ' help label provides an extender property, and the design-time ' framework will call this method once for each component to determine ' if we are interested in providing our extended properties for the ' component. We return true here if the object is a control and is ' not a HelpLabel (because it would not be meaningful to add this property to ' ourselves). ' </desc> ' </doc> ' Function CanExtend(ByVal target As Object) As Boolean Implements IExtenderProvider.CanExtend If TypeOf target Is Control And Not TypeOf target Is HelpLabel Then Return True End If Return False End Function ' ' <doc> ' <desc> ' This is the extended property for the HelpText property. Extended ' properties are actual methods because they take an additional parameter ' that is the object or control to provide the property for. ' </desc> ' </doc> ' <DefaultValue("")> _ Public Function GetHelpText(ByVal ctrl As Control) As String Dim myText As String = CStr(helpTexts(ctrl)) If myText Is Nothing Then myText = String.Empty End If Return myText End Function ' ' <doc> ' <desc> ' This is the extended property for the HelpText property. ' </desc> ' </doc> ' Public Sub SetHelpText(ByVal ctrl As Control, ByVal value As String) If value Is Nothing Then value = String.Empty End If If value.Length = 0 Then helpTexts.Remove(ctrl) RemoveHandler ctrl.Enter, AddressOf OnControlEnter RemoveHandler ctrl.Leave, AddressOf OnControlLeave Else helpTexts(ctrl) = value AddHandler ctrl.Enter, AddressOf OnControlEnter AddHandler ctrl.Leave, AddressOf OnControlLeave End If If ctrl Is activeControl Then Invalidate() End If End Sub ' ' <doc> ' <desc> ' This is an event handler that responds to the OnControlEnter ' event. We attach this to each control we are providing help ' text for. ' </desc> ' </doc> ' Private Sub OnControlEnter(ByVal sender As Object, ByVal e As EventArgs) activeControl = CType(sender, Control) Invalidate() End Sub ' ' <doc> ' <desc> ' This is an event handler that responds to the OnControlLeave ' event. We attach this to each control we are providing help ' text for. ' </desc> ' </doc> ' Private Sub OnControlLeave(ByVal sender As Object, ByVal e As EventArgs) If sender Is activeControl Then activeControl = Nothing Invalidate() End If End Sub ' ' <doc> ' <desc> ' Overrides Control.OnPaint. Here we draw our ' label. ' </desc> ' </doc> ' Protected Overrides Sub OnPaint(ByVal pe As PaintEventArgs) ' Let the base draw. This will cover our back ' color and set any image that the user has ' provided. ' MyBase.OnPaint(pe) ' Draw a rectangle around the control. ' Dim rect As Rectangle = ClientRectangle Dim borderPen As New Pen(ForeColor) pe.Graphics.DrawRectangle(borderPen, rect) borderPen.Dispose() ' Finally, draw the text over the top of the ' rectangle. ' If (activeControl IsNot Nothing) Then Dim myText As String = CStr(helpTexts(activeControl)) If (myText IsNot Nothing) And myText.Length > 0 Then rect.Inflate(-2, -2) Dim brush As New SolidBrush(ForeColor) pe.Graphics.DrawString(myText, Font, brush, RectangleF.op_Implicit(rect)) brush.Dispose() End If End If End Sub ' <doc> ' <desc> ' Returns true if backColor should be persisted in code gen. We ' override this because we change the default back color. ' </desc> ' <retvalue> ' true if the backColor should be persisted. ' </retvalue> ' </doc> ' Public Function ShouldSerializeBackColor() As Boolean Return Not BackColor.Equals(SystemColors.Info) End Function ' <doc> ' <desc> ' Returns true if foreColor should be persisted in code gen. We ' override this because we change the default foreground color. ' </desc> ' <retvalue> ' true if foreColor should be persisted. ' </retvalue> ' </doc> ' Public Function ShouldSerializeForeColor() As Boolean Return Not ForeColor.Equals(SystemColors.InfoText) End Function ' ' <doc> ' <desc> ' This is a designer for the HelpLabel. This designer provides ' design time feedback for the label. The help label responds ' to changes in the active control, but these events do not ' occur at design time. In order to provide some usable feedback ' that the control is working the right way, this designer listens ' to selection change events and uses those events to trigger active ' control changes. ' </desc> ' </doc> ' <System.Security.Permissions.PermissionSetAttribute(System.Security.Permissions.SecurityAction.Demand, Name:="FullTrust")> _ Public Class HelpLabelDesigner Inherits System.Windows.Forms.Design.ControlDesigner Private _trackSelection As Boolean = True ' <summary> ' This property is added to the control's set of properties in the method ' PreFilterProperties below. Note that on designers, properties that are ' explictly declared by TypeDescriptor.CreateProperty can be declared as ' private on the designer. This helps to keep the designer's public ' object model clean. ' </summary> Private Property TrackSelection() As Boolean Get Return _trackSelection End Get Set(ByVal Value As Boolean) _trackSelection = Value If _trackSelection Then Dim ss As ISelectionService = CType(GetService(GetType(ISelectionService)), ISelectionService) If (ss IsNot Nothing) Then UpdateHelpLabelSelection(ss) End If Else Dim helpLabel As HelpLabel = CType(Control, HelpLabel) If (helpLabel.activeControl IsNot Nothing) Then helpLabel.activeControl = Nothing helpLabel.Invalidate() End If End If End Set End Property Public Overrides ReadOnly Property Verbs() As DesignerVerbCollection Get Dim myVerbs() As DesignerVerb = {New DesignerVerb("Sample Verb", AddressOf OnSampleVerb)} Return New DesignerVerbCollection(myVerbs) End Get End Property ' ' <doc> ' <desc> ' Overrides Dispose. Here we remove our handler for the selection changed ' event. With designers, it is critical that they clean up any events they ' have attached. Otherwise, during the course of an editing session many ' designers might get created and never destroyed. ' </desc> ' </doc> ' Protected Overloads Overrides Sub Dispose(ByVal disposing As Boolean) If disposing Then Dim ss As ISelectionService = CType(GetService(GetType(ISelectionService)), ISelectionService) If (ss IsNot Nothing) Then RemoveHandler ss.SelectionChanged, AddressOf OnSelectionChanged End If End If MyBase.Dispose(disposing) End Sub ' ' <doc> ' <desc> ' Overrides initialize. Here we add an event handler to the selection service. ' Notice that we are very careful not to assume that the selection service is ' available. It is entirely optional that a service is available and you should ' always degrade gracefully if a service cannot be found. ' </desc> ' </doc> ' Public Overrides Sub Initialize(ByVal component As IComponent) MyBase.Initialize(component) Dim ss As ISelectionService = CType(GetService(GetType(ISelectionService)), ISelectionService) If (ss IsNot Nothing) Then AddHandler ss.SelectionChanged, AddressOf OnSelectionChanged End If End Sub Private Sub OnSampleVerb(ByVal sender As Object, ByVal e As EventArgs) MessageBox.Show("You have just invoked a sample verb. Normally, this would do something interesting.") End Sub ' ' <doc> ' <desc> ' The handler for the selection change event. Here we update the active control within ' the help label. ' </desc> ' </doc> ' Private Sub OnSelectionChanged(ByVal sender As Object, ByVal e As EventArgs) If _trackSelection Then Dim ss As ISelectionService = CType(sender, ISelectionService) UpdateHelpLabelSelection(ss) End If End Sub Protected Overrides Sub PreFilterProperties(ByVal properties As IDictionary) ' Always call base first in PreFilter* methods, and last in PostFilter* ' methods. MyBase.PreFilterProperties(properties) ' We add a design-time property called TrackSelection that is used to track ' the active selection. If the user sets this to true (the default), then ' we will listen to selection change events and update the control's active ' control to point to the current primary selection. properties("TrackSelection") = TypeDescriptor.CreateProperty( _ Me.GetType(), _ "TrackSelection", _ GetType(Boolean), _ New Attribute() {CategoryAttribute.Design}) End Sub ' <summary> ' This is a helper method that, given a selection service, will update the active control ' of the help label with the currently active selection. ' </summary> ' <param name="ss"></param> Private Sub UpdateHelpLabelSelection(ByVal ss As ISelectionService) Dim c As Control = CType(ss.PrimarySelection, Control) Dim helpLabel As HelpLabel = CType(Control, HelpLabel) If (c IsNot Nothing) Then helpLabel.activeControl = c helpLabel.Invalidate() Else If (helpLabel.activeControl IsNot Nothing) Then helpLabel.activeControl = Nothing helpLabel.Invalidate() End If End If End Sub Public Sub New() End Sub End Class End Class End Namespace
Windows 98, Windows Server 2000 SP4, Windows Millennium Edition, Windows Server 2003, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP SP2, Windows XP Starter Edition
The Microsoft .NET Framework 3.0 is supported on Windows Vista, Microsoft Windows XP SP2, and Windows Server 2003 SP1.