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Control.OnKeyPress Method

Raises the KeyPress event.

[Visual Basic]
Protected Overridable Sub OnKeyPress( _
   ByVal e As KeyPressEventArgs _
)
[C#]
protected virtual void OnKeyPress(
 KeyPressEventArgs e
);
[C++]
protected: virtual void OnKeyPress(
 KeyPressEventArgs* e
);
[JScript]
protected function OnKeyPress(
   e : KeyPressEventArgs
);

Parameters

e
A KeyPressEventArgs that contains the event data.

Remarks

Raising an event invokes the event handler through a delegate. For more information, see Raising an Event.

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

Example

[Visual Basic] 
' 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 

[C#] 
// 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;
    }
}


[C++] 
// 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;
   }
}

[JScript] No example is available for JScript. To view a Visual Basic, C#, or C++ example, click the Language Filter button Language Filter in the upper-left corner of the page.

Requirements

Platforms: Windows 98, Windows NT 4.0, Windows Millennium Edition, Windows 2000, Windows XP Home Edition, Windows XP Professional, Windows Server 2003 family, .NET Compact Framework

See Also

Control Class | Control Members | System.Windows.Forms Namespace | KeyPress

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