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KeyPressEventHandler Delegate

Represents the method that will handle the KeyPress event of a Control.

Namespace: System.Windows.Forms
Assembly: System.Windows.Forms (in system.windows.forms.dll)

public delegate void KeyPressEventHandler (
	Object sender,
	KeyPressEventArgs e
)
/** @delegate */
public delegate void KeyPressEventHandler (
	Object sender, 
	KeyPressEventArgs e
)
Not applicable.

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.


using System;
using System.Windows.Forms;

public class Form1: Form
{
    public Form1()
    {
        // Create a TextBox control.
        TextBox tb = new TextBox();
        this.Controls.Add(tb);
        tb.KeyPress += new KeyPressEventHandler(keypressed);
    }

    private 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.KeyChar == (char)Keys.Return)
        {
            e.Handled = true;
        }
    }

    public static void Main()
    {
        Application.Run(new 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 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;
    }
}


// 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 Server 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 Microsoft .NET Framework 3.0 is supported on Windows Vista, Microsoft Windows XP SP2, and Windows Server 2003 SP1.

.NET Framework

Supported in: 3.0, 2.0, 1.1, 1.0

.NET Compact Framework

Supported in: 2.0, 1.0

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