KeyEventArgs Class
Assembly: System.Windows.Forms (in system.windows.forms.dll)
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.
' This 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 filters for all variations ' of pressing the F1 key with a modifier key by using the KeyEventArgs properties passed ' to the event-handler method. ' 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. This example assumes ' that a TextBox control, named textBox1, has been added to the form and its KeyDown ' event has been contected to this event-handler method. Private Sub textBox1_KeyDown(ByVal sender As Object, ByVal e As System.Windows.Forms.KeyEventArgs) Handles textBox1.KeyDown ' Determine whether the key entered is the F1 key. If it is, display Help. If e.KeyCode = Keys.F1 AndAlso (e.Alt OrElse e.Control OrElse e.Shift) Then ' Display a pop-up Help topic to assist the user. Help.ShowPopup(textBox1, "Enter your name.", New Point(textBox1.Bottom, textBox1.Right)) ElseIf e.KeyCode = Keys.F2 AndAlso e.Modifiers = Keys.Alt Then ' 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, Me.textBox1.Left)) End If End Sub 'textBox1_KeyDown
// This 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 filters for all variations of pressing the F1 key with
// a modifier key by using the KeyEventArgs properties passed to the
// event handling method.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.
// This example assumes that a tTextBox control, named textBox1, has been
// added to the form and its KeyDown event has been contected to this
// event handling method.
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.get_KeyCode().Equals(Keys.F1) && (e.get_Alt() || e.get_Control()
|| e.get_Shift())) {
// Display a pop-up Help topic to assist the user.
Help.ShowPopup(textBox1, "Enter your name.", new Point(textBox1.
get_Bottom(), textBox1.get_Right()));
}
else {
if (e.get_KeyCode().Equals(Keys.F2) && e.get_Modifiers().
Equals(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.get_Top(), this.textBox1.get_Left()));
}
}
} //textBox1_KeyDown
} //Form1
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
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.get_Alt() && e.get_KeyCode() == Keys.E) {
treeView1.set_LabelEdit(true);
// If there is a TreeNode under the mose cursor, begin editing.
TreeNode editNode = treeView1.GetNodeAt(treeView1.PointToClient(
Control.get_MousePosition()));
if (editNode != null) {
editNode.BeginEdit();
}
}
} //treeView1_KeyDown
private void treeView1_AfterLabelEdit(Object sender,
NodeLabelEditEventArgs e)
{
// Disable the ability to edit the TreeNode labels.
treeView1.set_LabelEdit(false);
} //treeView1_AfterLabelEdit
' 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
// Boolean flag used to determine when a character other than a number
// is entered.
private boolean 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.get_KeyCode().CompareTo(Keys.D0)) < 0
|| (e.get_KeyCode().CompareTo(Keys.D9) > 0)) {
// Determine whether the keystroke is a number from the keypad.
if ((e.get_KeyCode().CompareTo(Keys.NumPad0) < 0
|| (e.get_KeyCode().CompareTo(Keys.NumPad9)) > 0)) {
// Determine whether the keystroke is a backspace.
if (!(e.get_KeyCode().Equals(Keys.Back))) {
// A non-numerical keystroke was pressed.
// Set the flag to true and evaluate in KeyPress event.
nonNumberEntered = true;
}
}
}
} //textBox1_KeyDown
// 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.set_Handled(true);
}
} //textBox1_KeyPress
Windows 98, Windows 2000 SP4, Windows CE, Windows Millennium Edition, Windows Mobile for Pocket PC, Windows Mobile for Smartphone, Windows Server 2003, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP SP2, Windows XP Starter Edition
The .NET Framework does not support all versions of every platform. For a list of the supported versions, see System Requirements.