Control.OnEnter(EventArgs) Control.OnEnter(EventArgs) Control.OnEnter(EventArgs) Control.OnEnter(EventArgs) Method

Definizione

Genera l'evento Enter.Raises the Enter event.

protected:
 virtual void OnEnter(EventArgs ^ e);
protected virtual void OnEnter (EventArgs e);
abstract member OnEnter : EventArgs -> unit
override this.OnEnter : EventArgs -> unit
Protected Overridable Sub OnEnter (e As EventArgs)

Parametri

e
EventArgs EventArgs EventArgs EventArgs

Oggetto EventArgs che contiene i dati dell'evento.An EventArgs that contains the event data.

Esempi

Il codice seguente viene illustrato come utilizzare il Enter eventi per modificare i colori di primo piano e sfondo di un TextBox in condizioni particolari.The following code example uses the Enter event to change the foreground and background colors of a TextBox under particular conditions.

private:
   void textBox1_Enter( Object^ /*sender*/, System::EventArgs^ /*e*/ )
   {
      // If the TextBox contains text, change its foreground and background colors.
      if ( textBox1->Text != String::Empty )
      {
         textBox1->ForeColor = Color::Red;
         textBox1->BackColor = Color::Black;

         // Move the selection pointer to the end of the text of the control.
         textBox1->Select(textBox1->Text->Length,0);
      }
   }

   void textBox1_Leave( Object^ /*sender*/, System::EventArgs^ /*e*/ )
   {
      // Reset the colors and selection of the TextBox after focus is lost.
      textBox1->ForeColor = Color::Black;
      textBox1->BackColor = Color::White;
      textBox1->Select(0,0);
   }
private void textBox1_Enter(object sender, System.EventArgs e)
{
    // If the TextBox contains text, change its foreground and background colors.
    if (!string.IsNullOrEmpty(textBox1.Text))
    {
        textBox1.ForeColor = Color.Red;
        textBox1.BackColor = Color.Black;
        // Move the selection pointer to the end of the text of the control.
        textBox1.Select(textBox1.Text.Length, 0);
    }
}

private void textBox1_Leave(object sender, System.EventArgs e)
{
    // Reset the colors and selection of the TextBox after focus is lost.
    textBox1.ForeColor = Color.Black;
    textBox1.BackColor = Color.White;
    textBox1.Select(0,0);
}
    Private Sub textBox1_Enter(sender As Object, e As System.EventArgs) Handles textBox1.Enter
        ' If the TextBox contains text, change its foreground and background colors.
        If textBox1.Text <> [String].Empty Then
            textBox1.ForeColor = Color.Red
            textBox1.BackColor = Color.Black
            ' Move the selection pointer to the end of the text of the control.
            textBox1.Select(textBox1.Text.Length, 0)
        End If
    End Sub 'textBox1_Enter
   
   
    Private Sub textBox1_Leave(sender As Object, e As System.EventArgs) Handles textBox1.Leave
        ' Reset the colors and selection of the TextBox after focus is lost.
        textBox1.ForeColor = Color.Black
        textBox1.BackColor = Color.White
        textBox1.Select(0, 0)
    End Sub 'textBox1_Leave
End Class 'Form1 

Commenti

Quando viene generato un evento, il gestore dell'evento viene richiamato tramite un delegato.Raising an event invokes the event handler through a delegate. Per altre informazioni, vedere la gestione e generazione di eventi.For more information, see Handling and Raising Events.

Il metodo OnEnter consente inoltre alle classi derivate di gestire l'evento senza associare un delegato.The OnEnter method also allows derived classes to handle the event without attaching a delegate. È la tecnica consigliata per la gestione dell'evento in una classe derivata.This is the preferred technique for handling the event in a derived class.

Note per gli eredi

Quando si esegue l'override di OnEnter(EventArgs) in una classe derivata, verificare di chiamare il metodo OnEnter(EventArgs) della classe di base in modo che i delegati registrati ricevano l'evento.When overriding OnEnter(EventArgs) in a derived class, be sure to call the base class's OnEnter(EventArgs) method so that registered delegates receive the event.

Si applica a

Vedi anche