ComboBox.WndProc(Message) Metodo

Definizione

Elabora i messaggi di Windows.Processes Windows messages.

protected:
 override void WndProc(System::Windows::Forms::Message % m);
protected override void WndProc (ref System.Windows.Forms.Message m);
override this.WndProc : Message -> unit
Protected Overrides Sub WndProc (ByRef m As Message)

Parametri

m
Message

Oggetto Message di Windows da elaborare.The Windows Message to process.

Esempi

Nell'esempio di codice riportato di seguito viene illustrato come eseguire l'override del metodo WndProc per gestire i messaggi del sistema operativo identificati nella struttura Message.The following code example demonstrates overriding the WndProc method to handle operating system messages identified in the Message structure. Il messaggio del sistema operativo WM_ACTIVATEAPP viene gestito in questo esempio per capire quando un'altra applicazione sta diventando attiva.The WM_ACTIVATEAPP operating system message is handled in this example to know when another application is becoming active. Per informazioni sui valori Message.Msg, Message.LParame Message.WParam disponibili, fare riferimento alla documentazione di Platform SDK disponibile in MSDN Library all'indirizzo https://msdn.microsoft.com/library.Refer to the Platform SDK documentation reference located in the MSDN library at https://msdn.microsoft.com/library to understand the available Message.Msg, Message.LParam, and Message.WParam values. I valori costanti effettivi sono reperibili nel file di intestazione Windows. h incluso nella sezione SDK di Platform SDK (Core SDK), disponibile anche in MSDN Library all'https://msdn.microsoft.com/library.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 in the MSDN library at https://msdn.microsoft.com/library.

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);
            }
        }

    [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);
        }
    }
}
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 metodo WndProc dopo essere stati filtrati tramite il metodo PreProcessMessage.All messages are sent to the WndProc method after getting filtered through the PreProcessMessage method.

Il metodo WndProc corrisponde esattamente alla funzione WindowProc di Windows.The WndProc method corresponds exactly to the Windows WindowProc function. Per ulteriori informazioni sull'elaborazione dei messaggi di Windows, vedere la documentazione relativa alla funzione WindowProc nel riferimento di Windows Platform SDK disponibile in MSDN Library all'https://msdn.microsoft.com/library.For more information about processing Windows messages, see the WindowProc function documentation in the Windows Platform SDK reference located in the MSDN library at https://msdn.microsoft.com/library.

Note per gli eredi

I controlli che ereditano devono chiamare il metodo WndProc(Message) della classe di base per elaborare tutti i messaggi che non gestiscono.Inheriting controls should call the base class's WndProc(Message) method to process any messages that they do not handle.

Sicurezza

SecurityPermission
per le classi che ereditano per chiamare codice non gestito.for inheriting classes to call unmanaged code. Enumerazione associata: UnmanagedCode.Associated enumeration: UnmanagedCode.

Si applica a

Vedi anche