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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)

public:
void AssignHandle (
	IntPtr handle
)
public void AssignHandle (
	IntPtr handle
)
public function AssignHandle (
	handle : IntPtr
)

Parameters

handle

The handle to assign to this window.

Exception typeCondition

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 form1ApplicationActivated 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.
ref class MyNativeWindowListener: public NativeWindow
{
private:

   // Constant value was found in the S"windows.h" header file.
   literal int WM_ACTIVATEAPP = 0x001C;
   Form1^ parent;

public:
   MyNativeWindowListener( Form1^ parent )
   {
      parent->HandleCreated += gcnew EventHandler( this, &MyNativeWindowListener::OnHandleCreated );
      parent->HandleDestroyed += gcnew EventHandler( this, &MyNativeWindowListener::OnHandleDestroyed );
      this->parent = parent;
   }

internal:

   // Listen for the control's window creation and then hook into it.
   void OnHandleCreated( Object^ sender, EventArgs^ /*e*/ )
   {
      // Window is now created, assign handle to NativeWindow.
      AssignHandle( (dynamic_cast<Form1^>(sender))->Handle );
   }

   void OnHandleDestroyed( Object^ /*sender*/, EventArgs^ /*e*/ )
   {
      // Window was destroyed, release hook.
      ReleaseHandle();
   }

protected:

   virtual void WndProc( Message %m ) override
   {
      // Listen for operating system messages
      switch ( m.Msg )
      {
         case WM_ACTIVATEAPP:

            // Notify the form that this message was received.
            // Application is activated or deactivated,
            // based upon the WParam parameter.
            parent->ApplicationActived( ((int)m.WParam != 0) );
            break;
      }
      NativeWindow::WndProc( m );
   }

};

// NativeWindow class to listen to operating system messages.
/** @attribute SecurityPermissionAttribute(SecurityAction.Demand, Flags=SecurityPermissionFlag.UnmanagedCode)
 */
public class MyNativeWindowListener extends NativeWindow
{
    // Constant value was found in the "windows.h" header file.
    private int WM_ACTIVATEAPP = 0x1C;
    private Form1 parent;

    public MyNativeWindowListener(Form1 parent)
    {
        parent.add_HandleCreated(new EventHandler(this.OnHandleCreated));
        parent.add_HandleDestroyed(new EventHandler(this.OnHandleDestroyed));
        this.parent = parent;
    } //MyNativeWindowListener

    // Listen for the control's window creation and then hook into it.
    void OnHandleCreated(Object sender, EventArgs e)
    {
        // Window is now created, assign handle to NativeWindow.
        AssignHandle(((Form1)sender).get_Handle());
    } //OnHandleCreated

    void OnHandleDestroyed(Object sender, EventArgs e)
    {
        // Window was destroyed, release hook.
        ReleaseHandle();
    } //OnHandleDestroyed

    protected void WndProc(Message m)
    {
        // Listen for operating system messages
        if (m.get_Msg() == WM_ACTIVATEAPP) {
            // Notify the form that this message was received.
            // Application is activated or deactivated, 
            // based upon the WParam parameter.
            parent.ApplicationActived(m.get_WParam().ToInt32() != 0);
        }
        super.WndProc(m);
    } //WndProc
} //MyNativeWindowListener

Windows 98, Windows 2000 SP4, Windows CE, Windows Millennium Edition, Windows Mobile for Pocket PC, Windows Mobile for Smartphone, Windows Server 2003, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP SP2, Windows XP Starter Edition

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

.NET Framework

Supported in: 2.0, 1.1, 1.0

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