IExtenderProvider.CanExtend(Object) Metodo
Definizione
Importante
Alcune informazioni sono relative alla release non definitiva del prodotto, che potrebbe subire modifiche significative prima della release definitiva. Microsoft non riconosce alcuna garanzia, espressa o implicita, in merito alle informazioni qui fornite.
Consente di specificare se questo oggetto può fornire le proprietà di estensione all'oggetto specificato.
public:
bool CanExtend(System::Object ^ extendee);public bool CanExtend (object extendee);abstract member CanExtend : obj -> boolPublic Function CanExtend (extendee As Object) As BooleanParametri
Restituisce
true se questo oggetto è in grado di fornire proprietà di estensione all'oggetto specificato; in caso contrario, false.
Esempio
Nell'esempio di codice seguente viene illustrato come implementare la CanExtend proprietà . Questo esempio fa parte di un esempio più ampio illustrato in Procedura: Implementare un provider extender HelpLabel.
namespace Microsoft.Samples.WinForms.Cs.HelpLabel
{
using System;
using System.Collections;
using System.ComponentModel;
using System.ComponentModel.Design;
using System.Drawing;
using System.Windows.Forms;
using System.Windows.Forms.Design;
//
// Help Label offers an extender property called
// "HelpText". It monitors the active control
// and displays the help text for the active control.
//
[
ProvideProperty("HelpText",typeof(Control)),
Designer(typeof(HelpLabel.HelpLabelDesigner))
]
public class HelpLabel : Control, System.ComponentModel.IExtenderProvider
{
/// <summary>
/// Required designer variable.
/// </summary>
private System.ComponentModel.Container components;
private Hashtable helpTexts;
private System.Windows.Forms.Control activeControl;
//
// Creates a new help label object.
//
public HelpLabel()
{
//
// Required for Windows Form Designer support
//
InitializeComponent();
helpTexts = new Hashtable();
}
/// <summary>
/// Clean up any resources being used.
/// </summary>
protected override void Dispose(bool disposing)
{
if (disposing)
{
components.Dispose();
}
base.Dispose(disposing);
}
/// <summary>
/// Required method for Designer support - do not modify
/// the contents of this method with the code editor.
/// </summary>
private void InitializeComponent()
{
this.BackColor = System.Drawing.SystemColors.Info;
this.components = new System.ComponentModel.Container ();
this.ForeColor = System.Drawing.SystemColors.InfoText;
this.TabStop = false;
}
//
// 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.
//
[
Browsable(false),
EditorBrowsable(EditorBrowsableState.Never),
DesignerSerializationVisibility(DesignerSerializationVisibility.Hidden)
]
public override string Text
{
get
{
return base.Text;
}
set
{
base.Text = value;
}
}
//
// 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 (since it would be silly to add this property to
// ourselves).
//
bool IExtenderProvider.CanExtend(object target)
{
if (target is Control &&
!(target is HelpLabel))
{
return true;
}
return false;
}
//
// 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.
//
[
DefaultValue(""),
]
public string GetHelpText(Control control)
{
string text = (string)helpTexts[control];
text ??= string.Empty;
return text;
}
//
// This is an event handler that responds to the OnControlEnter
// event. We attach this to each control we are providing help
// text for.
//
private void OnControlEnter(object sender, EventArgs e)
{
activeControl = (Control)sender;
Invalidate();
}
//
// This is an event handler that responds to the OnControlLeave
// event. We attach this to each control we are providing help
// text for.
//
private void OnControlLeave(object sender, EventArgs e)
{
if (sender == activeControl)
{
activeControl = null;
Invalidate();
}
}
//
// This is the extended property for the HelpText property.
//
public void SetHelpText(Control control, string value)
{
value ??= string.Empty;
if (value.Length == 0)
{
helpTexts.Remove(control);
control.Enter -= new EventHandler(OnControlEnter);
control.Leave -= new EventHandler(OnControlLeave);
}
else
{
helpTexts[control] = value;
control.Enter += new EventHandler(OnControlEnter);
control.Leave += new EventHandler(OnControlLeave);
}
if (control == activeControl)
{
Invalidate();
}
}
//
// Overrides Control.OnPaint. Here we draw our
// label.
//
protected override void OnPaint(PaintEventArgs pe)
{
// Let the base draw. This will cover our back
// color and set any image that the user may have
// provided.
//
base.OnPaint(pe);
// Draw a rectangle around our control.
//
Rectangle rect = ClientRectangle;
Pen borderPen = new Pen(ForeColor);
pe.Graphics.DrawRectangle(borderPen, rect);
borderPen.Dispose();
// Finally, draw the text over the top of the
// rectangle.
//
if (activeControl != null)
{
string text = (string)helpTexts[activeControl];
if (text != null && text.Length > 0)
{
rect.Inflate(-2, -2);
Brush brush = new SolidBrush(ForeColor);
pe.Graphics.DrawString(text, Font, brush, rect);
brush.Dispose();
}
}
}
// Returns true if the backColor should be persisted in code gen. We
// override this because we change the default back color.
// true if the backColor should be persisted.
//
public bool ShouldSerializeBackColor()
{
return(!BackColor.Equals(SystemColors.Info));
}
// Returns true if the foreColor should be persisted in code gen. We
// override this because we change the default foreground color.
// true if the foreColor should be persisted.
//
public bool ShouldSerializeForeColor()
{
return(!ForeColor.Equals(SystemColors.InfoText));
}
//
// 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.
//
public class HelpLabelDesigner : System.Windows.Forms.Design.ControlDesigner
{
private bool trackSelection = 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
/// explicitly declared by TypeDescriptor.CreateProperty can be declared as
/// private on the designer. This helps to keep the designer's public
/// object model clean.
/// </summary>
[DesignerSerializationVisibility( DesignerSerializationVisibility.Hidden )]
private bool TrackSelection
{
get
{
return trackSelection;
}
set
{
trackSelection = value;
if (trackSelection)
{
ISelectionService ss = (ISelectionService)GetService(typeof(ISelectionService));
if (ss != null)
{
UpdateHelpLabelSelection(ss);
}
}
else
{
HelpLabel helpLabel = (HelpLabel)Control;
if (helpLabel.activeControl != null)
{
helpLabel.activeControl = null;
helpLabel.Invalidate();
}
}
}
}
public override DesignerVerbCollection Verbs
{
get
{
DesignerVerb[] verbs = new DesignerVerb[] {
new DesignerVerb("Sample Verb", new EventHandler(OnSampleVerb))
};
return new DesignerVerbCollection(verbs);
}
}
//
// 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 may get created and never destroyed.
//
protected override void Dispose(bool disposing)
{
if (disposing)
{
ISelectionService ss = (ISelectionService)GetService(typeof(ISelectionService));
if (ss != null)
{
ss.SelectionChanged -= new EventHandler(OnSelectionChanged);
}
}
base.Dispose(disposing);
}
//
// 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 could not be found.
//
public override void Initialize(IComponent component)
{
base.Initialize(component);
ISelectionService ss = (ISelectionService)GetService(typeof(ISelectionService));
if (ss != null)
{
ss.SelectionChanged += new EventHandler(OnSelectionChanged);
}
}
private void OnSampleVerb(object sender, EventArgs e)
{
MessageBox.Show("You have just invoked a sample verb. Normally, this would do something interesting.");
}
//
// Our handler for the selection change event. Here we update the active control within
// the help label.
//
private void OnSelectionChanged(object sender, EventArgs e)
{
if (trackSelection)
{
ISelectionService ss = (ISelectionService)sender;
UpdateHelpLabelSelection(ss);
}
}
protected override void PreFilterProperties(IDictionary properties)
{
// Always call base first in PreFilter* methods, and last in PostFilter*
// methods.
base.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(
this.GetType(), // the type this property is defined on
"TrackSelection", // the name of the property
typeof(bool), // the type of the property
new Attribute[] {CategoryAttribute.Design}); // attributes
}
/// <summary>
/// This is a helper method that, given a selection service, will update the active control
/// of our help label with the currently active selection.
/// </summary>
/// <param name="ss"></param>
private void UpdateHelpLabelSelection(ISelectionService ss)
{
Control c = ss.PrimarySelection as Control;
HelpLabel helpLabel = (HelpLabel)Control;
if (c != null)
{
helpLabel.activeControl = c;
helpLabel.Invalidate();
}
else
{
if (helpLabel.activeControl != null)
{
helpLabel.activeControl = null;
helpLabel.Invalidate();
}
}
}
}
}
}
Option Strict On
Option Explicit On
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
'
' Help Label offers an extender property called
' HelpText. It monitors the active control
' and displays the help text for the active control.
'
<ProvideProperty("HelpText", GetType(Control)), Designer(GetType(HelpLabel.HelpLabelDesigner))> _
Public Class HelpLabel
Inherits Control
Implements System.ComponentModel.IExtenderProvider
' Required designer variable.
Private components As System.ComponentModel.Container
Private helpTexts As Hashtable
Private activeControl As System.Windows.Forms.Control
'
' Creates a new help label object.
'
Public Sub New()
'
' Required for Windows Form designer support.
'
InitializeComponent()
helpTexts = New Hashtable
End Sub
' Clean up any resources being used.
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
' Required method for designer support. Do not modify
' the contents of this method with the code editor.
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
'
' 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.
'
<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
'
' 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).
'
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
'
' 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.
'
<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
'
' This is the extended property for the HelpText property.
'
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
'
' This is an event handler that responds to the OnControlEnter
' event. We attach this to each control we are providing help
' text for.
'
Private Sub OnControlEnter(ByVal sender As Object, ByVal e As EventArgs)
activeControl = CType(sender, Control)
Invalidate()
End Sub
'
' This is an event handler that responds to the OnControlLeave
' event. We attach this to each control we are providing help
' text for.
'
Private Sub OnControlLeave(ByVal sender As Object, ByVal e As EventArgs)
If sender Is activeControl Then
activeControl = Nothing
Invalidate()
End If
End Sub
'
' Overrides Control.OnPaint. Here we draw our
' label.
'
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
' Returns true if backColor should be persisted in code gen. We
' override this because we change the default back color.
' true if the backColor should be persisted.
'
Public Function ShouldSerializeBackColor() As Boolean
Return Not BackColor.Equals(SystemColors.Info)
End Function
' Returns true if foreColor should be persisted in code gen. We
' override this because we change the default foreground color.
' true if foreColor should be persisted.
'
Public Function ShouldSerializeForeColor() As Boolean
Return Not ForeColor.Equals(SystemColors.InfoText)
End Function
'
' 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.
'
<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
' 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.
<DesignerSerializationVisibility(DesignerSerializationVisibility.Hidden)> _
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
'
' 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.
'
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
'
' 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.
'
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
'
' The handler for the selection change event. Here we update the active control within
' the help label.
'
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
' This is a helper method that, given a selection service, will update the active control
' of the help label with the currently active selection.
' <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
Commenti
Per altre informazioni sulle proprietà extender, vedere Procedura: Implementare un provider extender.
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