Message Structure
Implements a Windows message.
For a list of all members of this type, see Message Members.
System.Object
System.ValueType
System.Windows.Forms.Message
[Visual Basic] Public Structure Message [C#] public struct Message [C++] public __value struct Message
[JScript] In JScript, you can use the structures in the .NET Framework, but you cannot define your own.
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
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 structure directly. To create a Message structure, use the Create method. To make creating Message structures more efficient, the Message structure uses its pool of existing Message structures instead of instantiating a new one, if possible. However, if a Message structure is not available in the pool, a new structure is instantiated.
Example
[Visual Basic, C#, C++] The following example demonstrates overriding the WndProc method to handle operating system messages identified in the Message structure. The WM_ACTIVATEAPP operating system message is handled in this example to know when another application is becoming active. Refer to 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.
[Visual Basic] 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 [C#] using System; using System.Drawing; using System.Windows.Forms; namespace csTempWindowsApplication1 { public class Form1 : System.Windows.Forms.Form { // Constant value was found in the "windows.h" header file. private const int WM_ACTIVATEAPP = 0x001C; private bool appActive = true; [STAThread] static void Main() { Application.Run(new Form1()); } public Form1() { this.Size = new System.Drawing.Size(300,300); this.Text = "Form1"; this.Font = new System.Drawing.Font("Microsoft Sans Serif", 18F, System.Drawing.FontStyle.Bold, System.Drawing.GraphicsUnit.Point, ((System.Byte)(0))); } protected override void OnPaint(PaintEventArgs e) { // Paint a string in different styles depending on whether the // application is active. if (appActive) { e.Graphics.FillRectangle(SystemBrushes.ActiveCaption,20,20,260,50); e.Graphics.DrawString("Application is active", this.Font, SystemBrushes.ActiveCaptionText, 20,20); } else { e.Graphics.FillRectangle(SystemBrushes.InactiveCaption,20,20,260,50); e.Graphics.DrawString("Application is Inactive", this.Font, SystemBrushes.ActiveCaptionText, 20,20); } } [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) { // 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 = (((int)m.WParam != 0)); // Invalidate to get new text painted. this.Invalidate(); break; } base.WndProc(ref m); } } } [C++] using namespace System; using namespace System::Drawing; using namespace System::Windows::Forms; namespace csTempWindowsApplication1 { public __gc class Form1 : public System::Windows::Forms::Form { private: // Constant value was found in the S"windows.h" header file. const static Int32 WM_ACTIVATEAPP = 0x001C; Boolean appActive; public: Form1() { appActive = true; this->Size = System::Drawing::Size(300, 300); this->Text = S"Form1"; this->Font = new System::Drawing::Font(S"Microsoft Sans Serif", 18.0F, System::Drawing::FontStyle::Bold, System::Drawing::GraphicsUnit::Point, ((System::Byte)(0))); } protected: void OnPaint(PaintEventArgs* e) { // Paint a string in different styles depending on whether the // application is active. if (appActive) { e->Graphics->FillRectangle(SystemBrushes::ActiveCaption, 20, 20, 260, 50); e->Graphics->DrawString(S"Application is active", this->Font, SystemBrushes::ActiveCaptionText, 20, 20); } else { e->Graphics->FillRectangle(SystemBrushes::InactiveCaption, 20, 20, 260, 50); e->Graphics->DrawString(S"Application is Inactive", this->Font, SystemBrushes::ActiveCaptionText, 20, 20); } } [System::Security::Permissions::PermissionSet(System::Security::Permissions::SecurityAction::Demand, Name="FullTrust")] void WndProc(Message* m) { // Listen for operating system messages. switch (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 = (((int)m->WParam != 0)); // Invalidate to get new text painted. this->Invalidate(); break; } Form::WndProc(m); } }; } [STAThread] int main() { Application::Run(new csTempWindowsApplication1::Form1()); }
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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)