Export (0) Print
Expand All
1 out of 2 rated this helpful - Rate this topic

NativeWindow Class

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

For a list of all members of this type, see NativeWindow Members.

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

[Visual Basic]
Public Class NativeWindow
   Inherits MarshalByRefObject
[C#]
public class NativeWindow : MarshalByRefObject
[C++]
public __gc class NativeWindow : public MarshalByRefObject
[JScript]
public class NativeWindow extends MarshalByRefObject

Thread Safety

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

Remarks

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.

Example

[Visual Basic, C#, C++] The following 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 create two classes that inherit from NativeWindow that accomplish this.

[Visual Basic, C#, C++] 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 form1 ApplicationActivated method.

[Visual Basic, C#, C++] 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.

[Visual Basic] 
Imports System
Imports System.Drawing
Imports System.Windows.Forms
Imports System.Runtime.InteropServices

' Summary description for Form1.
Public Class Form1
    Inherits System.Windows.Forms.Form

    Private nwl As MyNativeWindowListener
    Private nw As MyNativeWindow

    Friend Sub ApplicationActived(ByVal ApplicationActivated As Boolean)
        ' The application has been activated or deactivated
        System.Diagnostics.Debug.WriteLine("Application Active = " + ApplicationActivated.ToString())
    End Sub

    Public Sub New()
        MyBase.New()

        Me.Size = New System.Drawing.Size(300, 300)
        Me.Text = "Form1"

        nwl = New MyNativeWindowListener(Me)
        nw = New MyNativeWindow(Me)

    End Sub

End Class

' NativeWindow class to listen to operating system messages.
Public 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.ApplicationActived(m.WParam.ToInt32() <> 0)

        End Select

        MyBase.WndProc(m)
    End Sub
End Class

' MyNativeWindow class to create a window given a class name.
Public Class MyNativeWindow
    Inherits NativeWindow

    ' Constant values were found in the "windows.h" header file.
    Private Const WS_CHILD As Integer = &H40000000, _
                  WS_VISIBLE As Integer = &H10000000, _
                  WM_ACTIVATEAPP As Integer = &H1C

    private windowHandle as integer

    Public Sub New(ByVal parent As Form)

        Dim cp As CreateParams = New 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 Or WS_VISIBLE

        ' Create the actual window
        Me.CreateHandle(cp)
    End Sub

    ' Listen to when the handle changes to keep the variable in sync
 <System.Security.Permissions.PermissionSetAttribute(System.Security.Permissions.SecurityAction.Demand, Name:="FullTrust")> _
Protected Overrides Sub OnHandleChange()
        windowHandle = Me.Handle.ToInt32()
    End Sub

<System.Security.Permissions.PermissionSetAttribute(System.Security.Permissions.SecurityAction.Demand, Name:="FullTrust")> _
    Protected Overrides Sub WndProc(ByRef m As Message)
        ' Listen for messages that are sent to the button window. Some messages are sent
        ' to the parent window instead of the button's window.

        Select Case (m.Msg)
            Case WM_ACTIVATEAPP
                ' Do something here in response to messages
        End Select

        MyBase.WndProc(m)
    End Sub

End Class

[C#] 
using System;
using System.Drawing;
using System.Windows.Forms;
using System.Runtime.InteropServices;

namespace NativeWindowApplication
{

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

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

        public Form1()
        {
            this.Size = new System.Drawing.Size(300,300);
            this.Text = "Form1";

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

        // The main entry point for the application.
        [STAThread]
        static void Main() 
        {
            Application.Run(new Form1());
        }
    }

    // NativeWindow class to listen to operating system messages.
    public class MyNativeWindowListener: NativeWindow{

        // Constant value was found in the "windows.h" header file.
        private const int WM_ACTIVATEAPP = 0x001C;

        private Form1 parent;

        public MyNativeWindowListener(Form1 parent){

            parent.HandleCreated += new EventHandler(this.OnHandleCreated);
            parent.HandleDestroyed+= new EventHandler(this.OnHandleDestroyed);
            this.parent = parent;
        }

        // Listen for the control's window creation and then hook into it.
        internal void OnHandleCreated(object sender, EventArgs e){
            // Window is now created, assign handle to NativeWindow.
            AssignHandle(((Form1)sender).Handle);
        }
        internal void OnHandleDestroyed(object sender, EventArgs e) {
            // Window was destroyed, release hook.
            ReleaseHandle();
        }
    [System.Security.Permissions.PermissionSet(System.Security.Permissions.SecurityAction.Demand, Name="FullTrust")]
        protected override void WndProc(ref Message m){
            // 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;                
            }
            base.WndProc(ref m);
        }        
    }

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

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

        public MyNativeWindow(Form parent){

            CreateParams cp = new 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);
        }

        // Listen to when the handle changes to keep the variable in sync
        [System.Security.Permissions.PermissionSet(System.Security.Permissions.SecurityAction.Demand, Name="FullTrust")]
        protected override void OnHandleChange(){
            windowHandle  = (int)this.Handle;
        }

    [System.Security.Permissions.PermissionSet(System.Security.Permissions.SecurityAction.Demand, Name="FullTrust")]
        protected override void WndProc(ref 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.

            switch (m.Msg){
                case WM_ACTIVATEAPP:
                    // Do something here in response to messages
                    break;
            }
            base.WndProc(ref m);
        }       
    }
}

[C++] 

using namespace System;
using namespace System::Drawing;
using namespace System::Windows::Forms;
using namespace System::Runtime::InteropServices;

__gc class MyNativeWindowListener;
__gc class MyNativeWindow;

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

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

public:
    Form1();
};

// NativeWindow class to listen to operating system messages.
__gc class MyNativeWindowListener : public NativeWindow {

    // Constant value was found in the S"windows.h" header file.
private:
    const static int  WM_ACTIVATEAPP = 0x001C;
    Form1*  parent;

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

    public private: 
        // 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:
    [System::Security::Permissions::PermissionSet(System::Security::Permissions::SecurityAction::Demand, Name="FullTrust")] 
    void WndProc(Message* m) {
        // 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.
__gc class MyNativeWindow : public NativeWindow {

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

    int windowHandle;

public:
    MyNativeWindow(Form* parent) {

        CreateParams* cp = new CreateParams();

        // Fill in the CreateParams details.
        cp->Caption = S"Click here";
        cp->ClassName = S"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
    [System::Security::Permissions::PermissionSet(System::Security::Permissions::SecurityAction::Demand, Name="FullTrust")] 
    void OnHandleChange() {
        windowHandle  = (int)this->Handle;
    }

    [System::Security::Permissions::PermissionSet(System::Security::Permissions::SecurityAction::Demand, Name="FullTrust")] 
    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.

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

// The main entry point for the application.
[STAThread]
int main() {
    Application::Run(new Form1());
}

[JScript] No example is available for JScript. To view a Visual Basic, C#, or C++ example, click the Language Filter button Language Filter in the upper-left corner of the page.

Requirements

Namespace: System.Windows.Forms

Platforms: Windows 98, Windows NT 4.0, Windows Millennium Edition, Windows 2000, Windows XP Home Edition, Windows XP Professional, Windows Server 2003 family

Assembly: System.Windows.Forms (in System.Windows.Forms.dll)

.NET Framework Security: 

See Also

NativeWindow Members | System.Windows.Forms Namespace

Did you find this helpful?
(1500 characters remaining)
Thank you for your feedback
Show:
© 2014 Microsoft. All rights reserved.