Control.KeyDown Event

 

Occurs when a key is pressed while the control has focus.

Namespace:   System.Windows.Forms
Assembly:  System.Windows.Forms (in System.Windows.Forms.dll)

Public Event KeyDown As KeyEventHandler

Key events occur in the following order:

  1. KeyDown

  2. KeyPress

  3. KeyUp

To handle keyboard events only at the form level and not enable other controls to receive keyboard events, set the KeyPressEventArgs.Handled property in your form's KeyPress event-handling method to true. Certain keys, such as the TAB, RETURN, ESC, and arrow keys are handled by controls automatically. To have these keys raise the KeyDown event, you must override the IsInputKey method in each control on your form. The code for the override of the IsInputKey would need to determine if one of the special keys is pressed and return a value of true. Instead of overriding the IsInputKey method, you can handle the PreviewKeyDown event and set the IsInputKeyproperty to true. For a code example, see the PreviewKeyDown event.

For more information about handling events, see Handling and Raising Events.

The following code example uses the KeyDown event to determine the type of character entered into the control.

' 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
    'If shift key was pressed, it's not a number.
    If Control.ModifierKeys = Keys.Shift Then
        nonNumberEntered = true
    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

.NET Framework
Available since 1.1
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