NativeWindow.ReleaseHandle Metoda

Definice

Obor názvů:

System.Windows.Forms

Sestavení:

System.Windows.Forms.dll

Uvolní popisovač přidružený k tomuto oknu.

public:
 virtual void ReleaseHandle();

public virtual void ReleaseHandle ();

abstract member ReleaseHandle : unit -> unit
override this.ReleaseHandle : unit -> unit

Public Overridable Sub ReleaseHandle ()

Příklady

Následující příklad kódu ukazuje zachycení zpráv okna operačního systému v proceduře okna. Příklad vytvoří třídu, která dědí z NativeWindow , aby to bylo možné.

Třída se MyNativeWindowListener připojí k proceduře okna formuláře předaného do konstruktoru a přepíše metodu WndProc k zachycení zprávy okna WM_ACTIVATEAPP . Třída demonstruje použití AssignHandle metod a ReleaseHandle k identifikaci okna popisovače, který NativeWindow bude používat. Popisovač se přiřazuje na Control.HandleCreated základě událostí a Control.HandleDestroyed . Při přijetí WM_ACTIVATEAPP zprávy okna volá třída metodu form1.ApplicationActivated .

Tento kód je výňatek z příkladu zobrazeného v přehledu NativeWindow třídy. Některý kód se nezobrazuje kvůli stručnosti. Celý výpis kódu najdete na stránce NativeWindow .

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

   // Constant value was found in the S"windows.h" header file.
   literal int WM_ACTIVATEAPP = 0x001C;
   Form1^ parent;

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

internal:

   // 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:

   virtual void WndProc( Message %m ) override
   {
      // 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 );
   }

};

// NativeWindow class to listen to operating system messages.
internal 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();
    }

    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.ApplicationActivated(((int)m.WParam != 0));

                break;
        }
        base.WndProc(ref m);
    }
}

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

        End Select

        MyBase.WndProc(m)
    End Sub
End Class

Poznámky

Tato metoda nezničí popisovač okna. Místo toho nastaví proceduru okna úchytu na výchozí proceduru okna. Handle Nastaví vlastnost na 0 a zavoláOnHandleChange, aby odrážela změnu.

Okno automaticky volá tuto metodu, pokud obdrží nativní win32 WM_NCDESTROY zprávu, která indikuje, že systém Windows zničil popisovač.

Viz také

• Handle
• AssignHandle(IntPtr)
• CreateHandle(CreateParams)
• DestroyHandle()
• WndProc(Message)
• OnHandleChange()
• Finalize()