OnKeyDown Method
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Control.OnKeyDown Method (KeyEventArgs)


Raises the KeyDown event.

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

Protected Overridable Sub OnKeyDown (
	e As KeyEventArgs


Type: System.Windows.Forms.KeyEventArgs

A KeyEventArgs that contains the event data.

Raising an event invokes the event handler through a delegate. For more information, see Handling and Raising Events.

The OnKeyDown method also allows derived classes to handle the event without attaching a delegate. This is the preferred technique for handling the event in a derived class.

Notes to Inheritors:

When overriding OnKeyDown in a derived class, be sure to call the base class's OnKeyDown method so that registered delegates receive the event.

Legacy Code Example

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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