protected:
virtual void OnKeyDown(System::Windows::Forms::KeyEventArgs ^ e);
protected virtual void OnKeyDown (System.Windows.Forms.KeyEventArgs e);
abstract member OnKeyDown : System.Windows.Forms.KeyEventArgs -> unit
override this.OnKeyDown : System.Windows.Forms.KeyEventArgs -> unit
Protected Overridable Sub OnKeyDown (e As KeyEventArgs)
下列程式碼範例會
KeyDown
使用 事件來判斷輸入控制項中的字元類型。
// 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;
//If shift key was pressed, it's not a number.
if (Control::ModifierKeys == Keys::Shift) {
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 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;
//If shift key was pressed, it's not a number.
if (Control.ModifierKeys == Keys.Shift) {
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 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
' 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
引發事件會透過委派叫用此事件處理常式。 如需詳細資訊，請參閱
處理和引發事件
。
OnKeyDown
方法也允許衍生類別處理事件，而不用附加委派。 這是在衍生類別中處理事件的慣用技巧。
給繼承者的注意事項
當在衍生類別中覆寫
OnKeyDown(KeyEventArgs)
時，請確定呼叫基底類別的
OnKeyDown(KeyEventArgs)
方法，使已註冊的委派能接收到事件。
