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NativeWindow.AssignHandle Method

Assigns a handle to this window.

Namespace:  System.Windows.Forms
Assembly:  System.Windows.Forms (in System.Windows.Forms.dll)
'Declaration
Public Sub AssignHandle ( _
	handle As IntPtr _
)

Parameters

handle
Type: System.IntPtr
The handle to assign to this window.
ExceptionCondition
Exception

This window already has a handle.

Win32Exception

The windows procedure for the associated native window could not be retrieved.

WndProc intercepts window messages sent to the handle parameter. Use ReleaseHandle to reset the handle's window procedure to the default window procedure.

The AssignHandle method calls the OnHandleChange method to indicate that the value of the Handle property has changed.

NoteNote

The handle to assign cannot be in a different application process.

The following code example demonstrates intercepting operating system window messages in a window procedure. The example creates a class that inherits from NativeWindow to accomplish this.

The MyNativeWindowListener class hooks into the window procedure of the form passed into the constructor, and overrides the WndProc method to intercepts the WM_ACTIVATEAPP window message. The class demonstrates the use of the AssignHandle and ReleaseHandle methods to identify which window handle the NativeWindow will use. The handle is assigned based upon the Control.HandleCreated and Control.HandleDestroyed events. When the WM_ACTIVATEAPP window message is received, the class calls the form1 ApplicationActivated method.

This code is an excerpt from the example shown in the NativeWindow class overview. Some code is not shown for the purpose of brevity. See NativeWindow for the whole code listing.


' NativeWindow class to listen to operating system messages.
Friend Class MyNativeWindowListener
    Inherits NativeWindow

    ' Constant value was found in the "windows.h" header file.
    Private Const WM_ACTIVATEAPP As Integer = &H1C

    Private parent As Form1

    Public Sub New(ByVal parent As Form1)

        AddHandler parent.HandleCreated, AddressOf Me.OnHandleCreated
        AddHandler parent.HandleDestroyed, AddressOf Me.OnHandleDestroyed
        Me.parent = parent
    End Sub

    ' Listen for the control's window creation and hook into it.    
    Private Sub OnHandleCreated(ByVal sender As Object, ByVal e As EventArgs)
        ' Window is now created, assign handle to NativeWindow.
        AssignHandle(CType(sender, Form).Handle)
    End Sub

    Private Sub OnHandleDestroyed(ByVal sender As Object, ByVal e As EventArgs)
        ' Window was destroyed, release hook.
        ReleaseHandle()
    End Sub

    <System.Security.Permissions.PermissionSetAttribute(System.Security.Permissions.SecurityAction.Demand, Name:="FullTrust")> _
        Protected Overrides Sub WndProc(ByRef m As Message)
        ' Listen for operating system messages

        Select Case (m.Msg)
            Case WM_ACTIVATEAPP

                ' Notify the form that this message was received.
                ' Application is activated or deactivated, 
                ' based upon the WParam parameter.
                parent.ApplicationActivated(m.WParam.ToInt32() <> 0)

        End Select

        MyBase.WndProc(m)
    End Sub
End Class


.NET Framework

Supported in: 4, 3.5, 3.0, 2.0, 1.1, 1.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows XP SP2 x64 Edition, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.
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