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KeyEventHandler Delegate

Represents the method that will handle the KeyUp or KeyDown event of a Control.

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

public delegate void KeyEventHandler(
	Object^ sender, 
	KeyEventArgs^ e


Type: System::Object
The source of the event.
Type: System.Windows.Forms::KeyEventArgs
A KeyEventArgs that contains the event data.

When you create a KeyEventHandler delegate, you identify the method that will handle the event. To associate the event with your event handler, add an instance of the delegate to the event. The event handler is called whenever the event occurs, unless you remove the delegate. For more information about handling events with delegates, see Events and Delegates.

   void treeView1_KeyDown( Object^ /*sender*/, KeyEventArgs^ e )
      /* If the 'Alt' and 'E' keys are pressed,
         * allow the user to edit the TreeNode label. */
      if ( e->Alt && e->KeyCode == Keys::E )
         treeView1->LabelEdit = true;

         // If there is a TreeNode under the mose cursor, begin editing.
         TreeNode^ editNode = treeView1->GetNodeAt( treeView1->PointToClient( Control::MousePosition ) );
         if ( editNode != nullptr )

   void treeView1_AfterLabelEdit( Object^ /*sender*/, NodeLabelEditEventArgs^ /*e*/ )
      // Disable the ability to edit the TreeNode labels.
      treeView1->LabelEdit = false;

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

.NET Framework

Supported in: 4, 3.5, 3.0, 2.0, 1.1, 1.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows XP SP2 x64 Edition, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.