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NativeWindow Class

Provides a low-level encapsulation of a window handle and a window procedure.

Namespace: System.Windows.Forms
Assembly: System.Windows.Forms (in system.windows.forms.dll)

'Declaration
Public Class NativeWindow
	Inherits MarshalByRefObject
	Implements IWin32Window
'Usage
Dim instance As NativeWindow

public class NativeWindow extends MarshalByRefObject implements IWin32Window
public class NativeWindow extends MarshalByRefObject implements IWin32Window

This class automatically manages window class creation and registration.

A window is not eligible for garbage collection when it is associated with a window handle. To ensure proper garbage collection, handles must either be destroyed manually using DestroyHandle or released using ReleaseHandle.

The NativeWindow class provides the following procedure and methods to manage handles: Handle, CreateHandle, AssignHandle, DestroyHandle, and ReleaseHandle.

The following code example demonstrates intercepting operating system window messages in a window procedure, and creating a window with a specific operating system window class name. The example creates two classes that inherit from NativeWindow that accomplish this.

The MyNativeWindowListener class hooks into the window procedure of the form passed into the constructor, and overrides the WndProc method to intercept the WM_ACTIVATEAPP window message. The class demonstrates the usage of the AssignHandle and ReleaseHandle methods to identify the window handle the NativeWindow will use. The handle is assign based upon the Control.HandleCreated and Control.HandleDestroyed events. When the WM_ACTIVATEAPP window message is received, the class calls the form1ApplicationActivated method.

The MyNativeWindow class creates a new window with the ClassName set to BUTTON. The class demonstrates using the CreateHandle method and overriding the WndProc method to intercept window messages that are received.

using namespace System;
using namespace System::Drawing;
using namespace System::Windows::Forms;
using namespace System::Runtime::InteropServices;
ref class MyNativeWindowListener;
ref class MyNativeWindow;

// Summary description for Form1.
ref class Form1: public System::Windows::Forms::Form
{
private:
   MyNativeWindowListener^ nwl;
   MyNativeWindow^ nw;

internal:
   void ApplicationActived( bool ApplicationActivated )
   {
      // The application has been activated or deactivated
      System::Diagnostics::Debug::WriteLine( "Application Active = {0}", ApplicationActivated.ToString() );
   }


public:
   Form1();
};

// 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 );
   }

};

// MyNativeWindow class to create a window given a class name.
ref class MyNativeWindow: public NativeWindow
{
private:

   // Constant values were found in the S"windows.h" header file.
   literal int WS_CHILD = 0x40000000,WS_VISIBLE = 0x10000000,WM_ACTIVATEAPP = 0x001C;
   int windowHandle;

public:
   MyNativeWindow( Form^ parent )
   {
      CreateParams^ cp = gcnew CreateParams;

      // Fill in the CreateParams details.
      cp->Caption = "Click here";
      cp->ClassName = "Button";

      // Set the position on the form
      cp->X = 100;
      cp->Y = 100;
      cp->Height = 100;
      cp->Width = 100;

      // Specify the form as the parent.
      cp->Parent = parent->Handle;

      // Create as a child of the specified parent
      cp->Style = WS_CHILD | WS_VISIBLE;

      // Create the actual window
      this->CreateHandle( cp );
   }

protected:

   // Listen to when the handle changes to keep the variable in sync

   virtual void OnHandleChange() override
   {
      windowHandle = (int)this->Handle;
   }

   virtual void WndProc( Message % m ) override
   {
      // Listen for messages that are sent to the button window. Some messages are sent
      // to the parent window instead of the button's window.
      switch ( m.Msg )
      {
         case WM_ACTIVATEAPP:
            
            // Do something here in response to messages
            break;
      }
      NativeWindow::WndProc( m );
   }
};

Form1::Form1()
{
   this->Size = System::Drawing::Size( 300, 300 );
   this->Text = "Form1";
   nwl = gcnew MyNativeWindowListener( this );
   nw = gcnew MyNativeWindow( this );
}

// The main entry point for the application.

[STAThread]
int main()
{
   Application::Run( gcnew Form1 );
}


package NativeWindowApplication;

import System.*;
import System.Drawing.*;
import System.Windows.Forms.*;
import System.Runtime.InteropServices.*;
import System.Security.Permissions.*;

// Summary description for Form1.

public class Form1 extends System.Windows.Forms.Form
{
    private MyNativeWindowListener nwl;
    private MyNativeWindow nw;

    void ApplicationActived(boolean applicationActivated)
    {
        // The application has been activated or deactivated
        System.Diagnostics.Debug.WriteLine("Application Active = " 
            + Convert.ToString(applicationActivated));
    } //ApplicationActived

    public Form1()
    {
        this.set_Size(new System.Drawing.Size(300, 300));
        this.set_Text("Form1");

        nwl = new MyNativeWindowListener(this);
        nw = new MyNativeWindow(this);
    } //Form1

    // The main entry point for the application.
    /** @attribute STAThread()
     */
    public static void main(String[] args)
    {
        Application.Run(new Form1());
    } //main
} //Form1

// 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

// MyNativeWindow class to create a window given a class name.
/** @attribute SecurityPermissionAttribute(SecurityAction.Demand, Flags=SecurityPermissionFlag.UnmanagedCode)
 */
public class MyNativeWindow extends NativeWindow
{
    // Constant values were found in the "windows.h" header file.
    private int WS_CHILD = 0x40000000;
    private int WS_VISIBLE = 0x10000000;
    private int WM_ACTIVATEAPP = 0x1C;
    private int windowHandle;

    public MyNativeWindow(Form parent)
    {
        CreateParams cp = new CreateParams();

        // Fill in the CreateParams details.
        cp.set_Caption("Click here");
        cp.set_ClassName("Button");

        // Set the position on the form
        cp.set_X(100);
        cp.set_Y(100);
        cp.set_Height(100);
        cp.set_Width(100);

        // Specify the form as the parent.
        cp.set_Parent(parent.get_Handle());

        // Create as a child of the specified parent
        cp.set_Style(WS_CHILD | WS_VISIBLE);

        // Create the actual window
        this.CreateHandle(cp);
    } //MyNativeWindow

    // Listen to when the handle changes to keep the variable in sync
    protected void OnHandleChange()
    {
        windowHandle = this.get_Handle().ToInt32();
    } //OnHandleChange

    protected void WndProc(Message m)
    {
        // Listen for messages that are sent to the button window. 
        // Some messages are sent to the parent window 
        // instead of the button's window.
        if (m.get_Msg() == WM_ACTIVATEAPP) {
            // Do something here in response to messages
        }
        super.WndProc(m);
    } //WndProc
} //MyNativeWindow

System.Object
   System.MarshalByRefObject
    System.Windows.Forms.NativeWindow

Any public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe.

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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