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KeyEventHandler Delegate

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

[Visual Basic]
<Serializable>
Public Delegate Sub KeyEventHandler( _
   ByVal sender As Object, _
   ByVal e As KeyEventArgs _
)
[C#]
[Serializable]
public delegate void KeyEventHandler(
   object sender,
   KeyEventArgs e
);
[C++]
[Serializable]
public __gc __delegate void KeyEventHandler(
   Object* sender,
   KeyEventArgs* e
);

[JScript] In JScript, you can use the delegates in the .NET Framework, but you cannot define your own.

Parameters [Visual Basic, C#, C++]

The declaration of your event handler must have the same parameters as the KeyEventHandler delegate declaration.

sender
The source of the event.
e
A KeyEventArgs that contains the event data.

Remarks

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.

Example

[Visual Basic] 
Private Sub treeView1_KeyDown(sender As Object, _
  e As KeyEventArgs) Handles treeView1.KeyDown
   ' If the 'Alt' and 'E' keys are pressed,
   ' allow the user to edit the TreeNode label. 
   If e.Alt And e.KeyCode = Keys.E Then
      treeView1.LabelEdit = True
      ' If there is a TreeNode under the mose cursor, begin editing. 
      Dim editNode As TreeNode = treeView1.GetNodeAt( _
        treeView1.PointToClient(Control.MousePosition))
      If Not (editNode Is Nothing) Then
         editNode.BeginEdit()
      End If
   End If
End Sub

Private Sub treeView1_AfterLabelEdit(sender As Object, _
  e As NodeLabelEditEventArgs) Handles treeView1.AfterLabelEdit
   ' Disable the ability to edit the TreeNode labels.
   treeView1.LabelEdit = False
End Sub

[C#] 
private 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 != null)
      { 
         editNode.BeginEdit();
      }
   }
}

private void treeView1_AfterLabelEdit(object sender, NodeLabelEditEventArgs e)
{
   // Disable the ability to edit the TreeNode labels.
   treeView1.LabelEdit = false;
}

[C++] 
private:
    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 != 0) {
                editNode->BeginEdit();
            }
        }
    }

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

[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

Namespace: System.Windows.Forms

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

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

See Also

System.Windows.Forms Namespace | OnKeyUp | KeyUp | OnKeyDown | KeyDown | KeyEventArgs | OnKeyPress | KeyPress | KeyPressEventArgs

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