ComboBox.WndProc(Message) Metodo
Definizione
Importante
Alcune informazioni sono relative alla release non definitiva del prodotto, che potrebbe subire modifiche significative prima della release definitiva. Microsoft non riconosce alcuna garanzia, espressa o implicita, in merito alle informazioni qui fornite.
Elabora i messaggi di Windows.
protected:
override void WndProc(System::Windows::Forms::Message % m);protected override void WndProc (ref System.Windows.Forms.Message m);override this.WndProc : Message -> unitProtected Overrides Sub WndProc (ByRef m As Message)Parametri
Esempio
Nell'esempio di codice seguente viene illustrato l'override del WndProc metodo per gestire i messaggi del sistema operativo identificati nella Message struttura. Il messaggio del sistema operativo WM_ACTIVATEAPP viene gestito in questo esempio per sapere quando un'altra applicazione sta diventando attiva. Fare riferimento alla documentazione di Platform SDK disponibile all'indirizzo https://learn.microsoft.com per comprendere i valori , Message.LParame Message.WParam disponibiliMessage.Msg. I valori costanti effettivi sono disponibili nel file di intestazione Windows.h incluso nel download di Platform SDK (Core SDK), disponibile anche in https://learn.microsoft.com.
using namespace System;
using namespace System::Drawing;
using namespace System::Windows::Forms;
using namespace System::Security::Permissions;
namespace csTempWindowsApplication1
{
public ref class Form1: public System::Windows::Forms::Form
{
private:
// Constant value was found in the "windows.h" header file.
static const Int32 WM_ACTIVATEAPP = 0x001C;
Boolean appActive;
public:
Form1()
{
appActive = true;
this->Size = System::Drawing::Size( 300, 300 );
this->Text = "Form1";
this->Font = gcnew System::Drawing::Font( "Microsoft Sans Serif",18.0F,System::Drawing::FontStyle::Bold,System::Drawing::GraphicsUnit::Point,((System::Byte)(0)) );
}
protected:
virtual void OnPaint( PaintEventArgs^ e ) override
{
// 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 );
}
}
[SecurityPermission(SecurityAction::Demand, Flags=SecurityPermissionFlag::UnmanagedCode)]
virtual void WndProc( Message% m ) override
{
// Listen for operating system messages.
switch ( m.Msg )
{
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( gcnew csTempWindowsApplication1::Form1 );
}
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);
}
}
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);
}
}
}
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
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
Commenti
Tutti i messaggi vengono inviati al WndProc metodo dopo essere stati filtrati tramite il PreProcessMessage metodo .
Il metodo WndProc corrisponde esattamente alla funzione WindowProc di Windows. Per altre informazioni sull'elaborazione dei messaggi di Windows, vedere la documentazione relativa alla funzione WindowProc nelle informazioni di riferimento su Windows Platform SDK.
Note per gli eredi
L'ereditarietà dei controlli deve chiamare il metodo della classe di WndProc(Message) base per elaborare i messaggi che non gestiscono.
