KeyPressEventHandler Delegate
Assembly: System.Windows.Forms (in system.windows.forms.dll)
'Declaration Public Delegate Sub KeyPressEventHandler ( _ sender As Object, _ e As KeyPressEventArgs _ ) 'Usage Dim instance As New KeyPressEventHandler(AddressOf HandlerMethod)
/** @delegate */ public delegate void KeyPressEventHandler ( Object sender, KeyPressEventArgs e )
JScript supports the use of delegates, but not the declaration of new ones.
Parameters
- sender
The source of the event.
- e
A KeyPressEventArgs that contains the event data.
Set KeyPressEventArgs.Handled to true to cancel the KeyPress event. This keeps the control from processing the key press.
When you create a KeyPressEventHandler 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.
Imports System Imports System.Windows.Forms Public Class Form1 Inherits Form Public Sub New() ' Create a TextBox control. Dim tb As New TextBox() Me.Controls.Add(tb) AddHandler tb.KeyPress, AddressOf keypressed End Sub 'New Private Sub keypressed(ByVal o As [Object], ByVal e As KeyPressEventArgs) ' The keypressed method uses the KeyChar property to check ' whether the ENTER key is pressed. ' If the ENTER key is pressed, the Handled property is set to true, ' to indicate the event is handled. If e.KeyChar = Microsoft.VisualBasic.ChrW(Keys.Return) Then e.Handled = True End If End Sub 'keypressed Public Shared Sub Main() Application.Run(New Form1()) End Sub 'Main End Class 'Form1
import System.*;
import System.Windows.Forms.*;
public class Form1 extends Form
{
public Form1()
{
// Create a TextBox control.
TextBox tb = new TextBox();
this.get_Controls().Add(tb);
tb.add_KeyPress(new KeyPressEventHandler(KeyPressed));
} //Form1
void KeyPressed(Object o, KeyPressEventArgs e)
{
// The keypressed method uses the KeyChar property to check
// whether the ENTER key is pressed.
// If the ENTER key is pressed, the Handled property is set to true,
// to indicate the event is handled.
if (e.get_KeyChar() == (char)(13)) {
e.set_Handled(true);
}
} // KeyPressed
public static void main(String[] args)
{
Application.Run(new Form1());
} //main
} //Form1
' 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.