Control.KeyDown-Ereignis

Tritt ein, wenn eine Taste gedrückt wird, während das Steuerelement den Fokus hat.

Namespace: System.Windows.Forms
Assembly: System.Windows.Forms (in system.windows.forms.dll)

Syntax

'Declaration
Public Event KeyDown As KeyEventHandler
'Usage
Dim instance As Control
Dim handler As KeyEventHandler

AddHandler instance.KeyDown, handler

public event KeyEventHandler KeyDown

public:
event KeyEventHandler^ KeyDown {
    void add (KeyEventHandler^ value);
    void remove (KeyEventHandler^ value);
}

/** @event */
public void add_KeyDown (KeyEventHandler value)

/** @event */
public void remove_KeyDown (KeyEventHandler value)

JScript unterstützt die Verwendung von Ereignissen, aber nicht die Deklaration von neuen Ereignissen.

Hinweise

Tastaturereignisse treten in der folgenden Reihenfolge ein:

1. KeyDown

2. KeyPress

3. KeyUp

Um Tastaturereignisse nur auf Formularebene zu behandeln und zu verhindern, dass andere Steuerelemente Tastaturereignisse empfangen, legen Sie die KeyPressEventArgs.Handled-Eigenschaft der KeyPress-Ereignisbehandlungsmethode des Formulars auf true fest. Bestimmte Tasten , z. B. die EINGABETASTE, TAB und ESC sowie die Pfeiltasten, werden von Steuerelementen automatisch behandelt. Damit diese Tasten das KeyDown-Ereignis auslösen, müssen Sie in jedem Steuerelement des Formulars die IsInputKey-Methode überschreiben. Der Code zum Überschreiben von IsInputKey muss bestimmen, ob eine der besonderen Tasten gedrückt wurde, und den Wert true zurückgeben.

Weitere Informationen zum Behandeln von Ereignissen finden Sie unter Behandeln von Ereignissen.

Beispiel

Im folgenden Codebeispiel wird das KeyDown-Ereignis verwendet, um den Typ des im Steuerelement eingegebenen Zeichens zu bestimmen.

    ' Boolean flag used to determine when a character other than a number is entered.
    Private nonNumberEntered As Boolean = False
   
   
    ' Handle the KeyDown event to determine the type of character entered into the control.
    Private Sub textBox1_KeyDown(sender As Object, e As System.Windows.Forms.KeyEventArgs) _
         Handles textBox1.KeyDown
        ' Initialize the flag to false.
        nonNumberEntered = False
      
        ' Determine whether the keystroke is a number from the top of the keyboard.
        If e.KeyCode < Keys.D0 OrElse e.KeyCode > Keys.D9 Then
            ' Determine whether the keystroke is a number from the keypad.
            If e.KeyCode < Keys.NumPad0 OrElse e.KeyCode > Keys.NumPad9 Then
                ' Determine whether the keystroke is a backspace.
                If e.KeyCode <> Keys.Back Then
                    ' A non-numerical keystroke was pressed. 
                    ' Set the flag to true and evaluate in KeyPress event.
                    nonNumberEntered = True
                End If
            End If
        End If
    End Sub 'textBox1_KeyDown
   
   
    ' This event occurs after the KeyDown event and can be used 
    ' to prevent characters from entering the control.
    Private Sub textBox1_KeyPress(sender As Object, e As System.Windows.Forms.KeyPressEventArgs) _
        Handles textBox1.KeyPress
        ' Check for the flag being set in the KeyDown event.
        If nonNumberEntered = True Then
            ' Stop the character from being entered into the control since it is non-numerical.
            e.Handled = True
        End If
    End Sub 'textBox1_KeyPress
End Class 'Form1 

// Boolean flag used to determine when a character other than a number is entered.
private bool nonNumberEntered = false;

// Handle the KeyDown event to determine the type of character entered into the control.
private void textBox1_KeyDown(object sender, System.Windows.Forms.KeyEventArgs e)
{
    // Initialize the flag to false.
    nonNumberEntered = false;

    // Determine whether the keystroke is a number from the top of the keyboard.
    if (e.KeyCode < Keys.D0 || e.KeyCode > Keys.D9)
    {
        // Determine whether the keystroke is a number from the keypad.
        if (e.KeyCode < Keys.NumPad0 || e.KeyCode > Keys.NumPad9)
        {
            // Determine whether the keystroke is a backspace.
            if(e.KeyCode != Keys.Back)
            {
                // A non-numerical keystroke was pressed.
                // Set the flag to true and evaluate in KeyPress event.
                nonNumberEntered = true;
            }
        }
    }
}

// This event occurs after the KeyDown event and can be used to prevent
// characters from entering the control.
private void textBox1_KeyPress(object sender, System.Windows.Forms.KeyPressEventArgs e)
{
    // Check for the flag being set in the KeyDown event.
    if (nonNumberEntered == true)
    {
        // Stop the character from being entered into the control since it is non-numerical.
        e.Handled = true;
    }
}

   // Boolean flag used to determine when a character other than a number is entered.
private:
   bool nonNumberEntered;

   // Handle the KeyDown event to determine the type of character entered into the control.
   void textBox1_KeyDown( Object^ /*sender*/, System::Windows::Forms::KeyEventArgs^ e )
   {
      // Initialize the flag to false.
      nonNumberEntered = false;

      // Determine whether the keystroke is a number from the top of the keyboard.
      if ( e->KeyCode < Keys::D0 || e->KeyCode > Keys::D9 )
      {
         // Determine whether the keystroke is a number from the keypad.
         if ( e->KeyCode < Keys::NumPad0 || e->KeyCode > Keys::NumPad9 )
         {
            // Determine whether the keystroke is a backspace.
            if ( e->KeyCode != Keys::Back )
            {
               // A non-numerical keystroke was pressed.
               // Set the flag to true and evaluate in KeyPress event.
               nonNumberEntered = true;
            }
         }
      }
   }

   // This event occurs after the KeyDown event and can be used to prevent
   // characters from entering the control.
   void textBox1_KeyPress( Object^ /*sender*/, System::Windows::Forms::KeyPressEventArgs^ e )
   {
      // Check for the flag being set in the KeyDown event.
      if ( nonNumberEntered == true )
      {         // Stop the character from being entered into the control since it is non-numerical.
         e->Handled = true;
      }
   }

// Boolean flag used to determine when a character other than a number 
// is entered.
private boolean nonNumberEntered = false;

// Handle the KeyDown event to determine the type of character entered 
// into the control.
private void textBox1_KeyDown(Object sender, 
    System.Windows.Forms.KeyEventArgs e)
{
    // Initialize the flag to false.
    nonNumberEntered = false;

    // Determine whether the keystroke is a number from the top of the 
    // keyboard.
    if ((e.get_KeyCode().CompareTo(Keys.D0)) < 0 
        || (e.get_KeyCode().CompareTo(Keys.D9) > 0)) {

        // Determine whether the keystroke is a number from the keypad.
        if ((e.get_KeyCode().CompareTo(Keys.NumPad0) < 0 
            || (e.get_KeyCode().CompareTo(Keys.NumPad9)) > 0)) {

            // Determine whether the keystroke is a backspace.
            if (!(e.get_KeyCode().Equals(Keys.Back))) {
                    // A non-numerical keystroke was pressed.
                    // Set the flag to true and evaluate in KeyPress event.
                    nonNumberEntered = true;
            }
        }
    }
} //textBox1_KeyDown

// This event occurs after the KeyDown event and can be used to prevent
// characters from entering the control.
private void textBox1_KeyPress(Object sender, System.Windows.Forms.
    KeyPressEventArgs e)
{
    // Check for the flag being set in the KeyDown event.
    if (nonNumberEntered == true) {
        // Stop the character from being entered into the control since 
        // it is non-numerical.
        e.set_Handled(true);
    }
} //textBox1_KeyPress

Plattformen

Windows 98, Windows 2000 SP4, Windows CE, Windows Millennium Edition, Windows Mobile für Pocket PC, Windows Mobile für Smartphone, Windows Server 2003, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP SP2, Windows XP Starter Edition

.NET Framework unterstützt nicht alle Versionen sämtlicher Plattformen. Eine Liste der unterstützten Versionen finden Sie unter Systemanforderungen.

Versionsinformationen

.NET Framework

Unterstützt in: 2.0, 1.1, 1.0

.NET Compact Framework

Unterstützt in: 2.0, 1.0

Siehe auch

Referenz

Control-Klasse
Control-Member
System.Windows.Forms-Namespace
KeyEventArgs
OnKeyDown
KeyUp
KeyPress