KeyPressEventHandler Delegado

Definición

Espacio de nombres:

System.Windows.Forms

Ensamblado:

System.Windows.Forms.dll

Source:

KeyPressEventHandler.cs

Representa el método que controlará el evento KeyPress de Control.

C#

public delegate void KeyPressEventHandler(object? sender, KeyPressEventArgs e);

Parámetros

sender

Object

Origen del evento.

e

KeyPressEventArgs

Objeto KeyPressEventArgs que contiene los datos del evento.

Ejemplos

C#

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());
    }
}

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;
            }
        }
    }
    //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)
    {
        // Stop the character from being entered into the control since it is non-numerical.
        e.Handled = true;
    }
}

Comentarios

Establézcalo KeyPressEventArgs.Handled en true para cancelar el KeyPress evento. Esto evita que el control procese la tecla.

Cuando se crea un delegado KeyPressEventHandler, se identifica el método que controlará el evento. Para asociar el evento al controlador, se debe agregar una instancia del delegado al evento. Siempre que se produce el evento, se llama a su controlador, a menos que se quite el delegado. Para obtener más información sobre cómo controlar eventos con delegados, vea Control y generación de eventos.

Métodos de extensión

Se aplica a

Consulte también

• OnKeyPress(KeyPressEventArgs)
• KeyPress
• KeyPressEventArgs
• OnKeyDown(KeyEventArgs)
• KeyDown
• OnKeyUp(KeyEventArgs)
• KeyUp
• KeyEventArgs