Message Structure
Assembly: System.Windows.Forms (in system.windows.forms.dll)
The Message structure wraps messages that Windows sends. You can use this structure to wrap a message and assign it to the window procedure to be dispatched. You can also use this structure to get information about a message the system sends to your application or controls.
You cannot create the Message directly. Instead, use the Create method. For the sake of efficiency, the Message uses its pool of existing Messages instead of instantiating a new one, if possible. However, if a Message is not available in the pool, a new one is instantiated.
The following code example demonstrates overriding the WndProc method to handle operating system messages identified in the Message. The WM_ACTIVATEAPP operating system message is handled in this example to know when another application is becoming active. See the Platform SDK documentation reference located in the MSDN Library to understand the available Message.Msg, Message.LParam, and Message.WParam values. Actual constant values can be found in the Windows.h header file included in the Platform SDK (Core SDK section) download, which is also available on MSDN.
Imports System Imports System.Drawing Imports System.Windows.Forms Namespace csTempWindowsApplication1 Public Class Form1 Inherits System.Windows.Forms.Form ' Constant value was found in the "windows.h" header file. Private Const WM_ACTIVATEAPP As Integer = &H1C Private appActive As Boolean = True <STAThread()> _ Shared Sub Main() Application.Run(New Form1()) End Sub 'Main Public Sub New() MyBase.New() Me.Size = New System.Drawing.Size(300, 300) Me.Text = "Form1" Me.Font = New System.Drawing.Font("Microsoft Sans Serif", 18.0!, System.Drawing.FontStyle.Bold, System.Drawing.GraphicsUnit.Point, CType(0, Byte)) End Sub Protected Overrides Sub OnPaint(ByVal e As PaintEventArgs) ' Paint a string in different styles depending on whether the ' application is active. If (appActive) Then e.Graphics.FillRectangle(SystemBrushes.ActiveCaption, 20, 20, 260, 50) e.Graphics.DrawString("Application is active", Me.Font, SystemBrushes.ActiveCaptionText, 20, 20) Else e.Graphics.FillRectangle(SystemBrushes.InactiveCaption, 20, 20, 260, 50) e.Graphics.DrawString("Application is Inactive", Me.Font, SystemBrushes.ActiveCaptionText, 20, 20) End If 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) ' The WM_ACTIVATEAPP message occurs when the application ' becomes the active application or becomes inactive. Case WM_ACTIVATEAPP ' The WParam value identifies what is occurring. appActive = (m.WParam.ToInt32() <> 0) ' Invalidate to get new text painted. Me.Invalidate() End Select MyBase.WndProc(m) End Sub End Class End Namespace
package JSLTempWindowsApplication1;
import System.*;
import System.Drawing.*;
import System.Windows.Forms.*;
import System.Security.Permissions.*;
public class Form1 extends System.Windows.Forms.Form
{
// Constant value was found in the "windows.h" header file.
private final int WM_ACTIVATEAPP = 0x1C;
private boolean appActive = true;
/** @attribute STAThread()
*/
public static void main(String[] args)
{
Application.Run(new Form1());
} //main
public Form1()
{
this.set_Size(new System.Drawing.Size(300, 300));
this.set_Text("Form1");
this.set_Font(new System.Drawing.Font("Microsoft Sans Serif", 18,
System.Drawing.FontStyle.Bold, System.Drawing.GraphicsUnit.Point,
(ubyte)0));
} //Form1
protected void OnPaint(PaintEventArgs e)
{
// Paint a string in different styles depending on whether the
// application is active.
if (appActive) {
e.get_Graphics().FillRectangle(SystemBrushes.get_ActiveCaption(),
20, 20, 260, 50);
e.get_Graphics().DrawString("Application is active",
this.get_Font(), SystemBrushes.get_ActiveCaptionText(),
20, 20);
}
else {
e.get_Graphics().FillRectangle(SystemBrushes.get_InactiveCaption(),
20, 20, 260, 50);
e.get_Graphics().DrawString("Application is Inactive",
this.get_Font(), SystemBrushes.get_ActiveCaptionText(),
20, 20);
}
} //OnPaint
/** @attribute SecurityPermissionAttribute(SecurityAction.Demand, Flags=SecurityPermissionFlag.UnmanagedCode)
*/
protected void WndProc(/** @ref */Message m)
{
// Listen for operating system messages.
switch (m.get_Msg()) {
// The WM_ACTIVATEAPP message occurs when the application
// becomes the active application or becomes inactive.
case WM_ACTIVATEAPP:
// The WParam value identifies what is occurring.
appActive = m.get_WParam().ToInt32() != 0;
// Invalidate to get new text painted.
this.Invalidate();
break;
}
super.WndProc(m);
} //WndProc
} //Form1
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.