Export (0) Print
Expand All
1 out of 2 rated this helpful - Rate this topic

KeyEventArgs Class

Provides data for the KeyDown or KeyUp event.

System.Object
  System.EventArgs
    System.Windows.Forms.KeyEventArgs

Namespace:  System.Windows.Forms
Assembly:  System.Windows.Forms (in System.Windows.Forms.dll)
[ComVisibleAttribute(true)]
public class KeyEventArgs : EventArgs

The KeyEventArgs type exposes the following members.

  NameDescription
Public methodKeyEventArgsInitializes a new instance of the KeyEventArgs class.
Top
  NameDescription
Public propertyAltGets a value indicating whether the ALT key was pressed.
Public propertyControlGets a value indicating whether the CTRL key was pressed.
Public propertyHandledGets or sets a value indicating whether the event was handled.
Public propertyKeyCodeGets the keyboard code for a KeyDown or KeyUp event.
Public propertyKeyDataGets the key data for a KeyDown or KeyUp event.
Public propertyKeyValueGets the keyboard value for a KeyDown or KeyUp event.
Public propertyModifiersGets the modifier flags for a KeyDown or KeyUp event. The flags indicate which combination of CTRL, SHIFT, and ALT keys was pressed.
Public propertyShiftGets a value indicating whether the SHIFT key was pressed.
Public propertySuppressKeyPressGets or sets a value indicating whether the key event should be passed on to the underlying control.
Top
  NameDescription
Public methodEquals(Object)Determines whether the specified Object is equal to the current Object. (Inherited from Object.)
Protected methodFinalizeAllows an object to try to free resources and perform other cleanup operations before it is reclaimed by garbage collection. (Inherited from Object.)
Public methodGetHashCodeServes as a hash function for a particular type. (Inherited from Object.)
Public methodGetTypeGets the Type of the current instance. (Inherited from Object.)
Protected methodMemberwiseCloneCreates a shallow copy of the current Object. (Inherited from Object.)
Public methodToStringReturns a string that represents the current object. (Inherited from Object.)
Top

A KeyEventArgs, which specifies the key the user pressed and whether any modifier keys (CTRL, ALT, and SHIFT) were pressed at the same time, is passed with each KeyDown or KeyUp event.

The KeyDown event occurs when the user presses any key. The KeyUp event occurs when the user releases the key. Duplicate KeyDown events occur each time the key repeats, if the key is held down, but only one KeyUp event is generated when the user releases the key.

The KeyPress event also occurs when a key is pressed. A KeyPressEventArgs is passed with each KeyPress event, and specifies the character that was composed as a result of each key press.

For information about the event model, see Events and Delegates.

The following code examples demonstrate how to detect the state of a key press.

Example 1

The following code example demonstrates how to use the KeyDown event with the Help class to display pop-up style Help to the user of the application. The example uses the KeyEventArgs properties passed to the event handler method to filter for all variations of pressing the F1 key with a modifier key. When the user presses any variation of F1 that includes any keyboard modifier, the Help class displays a pop-up window, similar to a ToolTip, near the control. If the user presses ALT+F2, a different Help pop-up is displayed with additional information.


private void textBox1_KeyDown(object sender, System.Windows.Forms.KeyEventArgs e)
{
    // Determine whether the key entered is the F1 key. If it is, display Help.
    if(e.KeyCode == Keys.F1 && (e.Alt || e.Control || e.Shift))
    {
        // Display a pop-up Help topic to assist the user.
        Help.ShowPopup(textBox1, "Enter your name.", new Point(textBox1.Bottom, textBox1.Right));
    }
    else if(e.KeyCode == Keys.F2 && e.Modifiers == Keys.Alt)
    {
        // Display a pop-up Help topic to provide additional assistance to the user.
        Help.ShowPopup(textBox1, "Enter your first name followed by your last name. Middle name is optional.",
            new Point(textBox1.Top, this.textBox1.Left));
    }
}


Example 2

The following example determines whether the user pressed ALT+E, and if the mouse pointer is over a TreeNode, allows the user to edit that TreeNode.


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(System.Windows.Forms.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;
}


Example 3

The following example determines whether the user pressed a non-numeric key, and if so, cancels the KeyPress event by using the Handled property.


        // 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;
            }
        }



.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.
Any public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe.
Did you find this helpful?
(1500 characters remaining)
Thank you for your feedback

Community Additions

ADD
Show:
© 2014 Microsoft. All rights reserved.