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How to prevent key backtracking in a TextBox?

I want to suppress a key stroke in a TextBox. To suppress all keystrokes except Backspace, I use the following:

    private void KeyBox_KeyDown(object sender, System.Windows.Input.KeyEventArgs e)
    {
        e.Handled = true;
    }

However, I only want to suppress keystrokes when the Backspace key is pressed. I am using the following:

        if (e.Key == System.Windows.Input.Key.Back)
        {
            e.Handled = true;
        }

However, this does not work. The character behind the start of the selection is still deleted. I get "TRUE" on the output, so the back key is recognized. How can I prevent a user from pressing backspace? (My consideration is that in some cases I want to delete words instead of characters, and therefore I need to process the return key by pressing it myself).

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7 answers

, , .

- , , , KeyDown, TextChanged KeyUp.

:

    string m_TextBeforeTheChange;
    int m_CursorPosition = 0;
    bool m_BackPressed = false;

    private void KeyBox_KeyDown(object sender, System.Windows.Input.KeyEventArgs e)
    {
        m_TextBeforeTheChange = KeyBox.Text;
        m_BackPressed = (e.Key.Equals(System.Windows.Input.Key.Back)) ? true : false;
    }

    private void KeyBox_TextChanged(object sender, TextChangedEventArgs e)
    {
        if (m_BackPressed)
        {
            m_CursorPosition = KeyBox.SelectionStart;
            KeyBox.Text = m_TextBeforeTheChange;
        }
    }

    private void KeyBox_KeyUp(object sender, System.Windows.Input.KeyEventArgs e)
    {
        KeyBox.SelectionStart = (m_BackPressed) ? m_CursorPosition + 1 : KeyBox.SelectionStart;
    }
0

e.SuppressKeyPress = true ( KeyDown), . Ex, backspace , :

private void textBox1_KeyDown(object sender, KeyEventArgs e)
{
    if (e.KeyCode == Keys.Back)
    {
        e.SuppressKeyPress = true;
    }
}
+14

Silverlight , backspace. , .

+3

, . , , , , , , .

    private string textBeforeChange;

    private void TextBox1_OnKeyDown(object sender, KeyEventArgs e)
    {
        if (e.Key == Key.Back)
        {
            e.Handled = true;
            textBox1.Text = textBeforeChange;
        }
    }

    private void TextBox1_OnKeyUp(object sender, KeyEventArgs e)
    {
        textBeforeChange = textBox1.Text;
    }

    private void MainPage_OnLoaded(object sender, RoutedEventArgs e)
    {
        textBox1.AddHandler(TextBox.KeyDownEvent, new KeyEventHandler(TextBox1_OnKeyDown), true);
        textBox1.AddHandler(TextBox.KeyUpEvent, new KeyEventHandler(TextBox1_OnKeyUp), true);
        textBox1.AddHandler(TextBox.ManipulationStartedEvent, new EventHandler<ManipulationStartedEventArgs>(TextBox1_OnManipulationStarted), true);
    }

    private void TextBox1_OnManipulationStarted(object sender, ManipulationStartedEventArgs e)
    {
        textBeforeChange = textBox1.Text;
    }
+1
    string oldText = "";
    private void testTextBlock_TextChanged(object sender, TextChangedEventArgs e)
    {
        if (testTextBlock.Text.Length < oldText.Length)
        {
            testTextBlock.Text = oldText;
            testTextBlock.SelectionStart = oldText.Length;
        }
        else
        {
            oldText = testTextBlock.Text;
        }
    }
0

, (Ctrl Backspace) (Ctrl Delete), (0x09, 0x20, 0xA0):

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace DeleteWord
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void textBox1_KeyDown(object sender, KeyEventArgs e)
        {
            // Tab, space, line feed
            char[] whitespace = {'\x09', '\x20', '\xA0'};
            string text = textBox1.Text;
            int start = textBox1.SelectionStart;

            if ((e.KeyCode == Keys.Back || e.KeyCode == Keys.Delete) && textBox1.SelectionLength > 0)
            {
                e.SuppressKeyPress = true;
                textBox1.Text = text.Substring(0, start) + text.Substring(start + textBox1.SelectionLength);
                textBox1.SelectionStart = start;
                return;
            }

            else if (e.KeyCode == Keys.Back && e.Control)
            {
                e.SuppressKeyPress = true;

                if (start == 0) return;

                int pos = Math.Max(text.LastIndexOfAny(whitespace, start - 1), 0);

                while (pos > 0)
                {
                    if (!whitespace.Contains(text[pos]))
                    {
                        pos++;
                        break;
                    }
                    pos--;
                }

                textBox1.Text = text.Substring(0, pos) + text.Substring(start);
                textBox1.SelectionStart = pos;
            }
            else if (e.KeyCode == Keys.Delete && e.Control)
            {
                e.SuppressKeyPress = true;

                int last = text.Length - 1;

                int pos = text.IndexOfAny(whitespace, start);
                if (pos == -1) pos = last + 1;

                while (pos <= last)
                {
                    if (!whitespace.Contains(text[pos])) break;
                    pos++;
                }

                textBox1.Text = text.Substring(0, start) + text.Substring(pos);
                textBox1.SelectionStart = start;
            }
        }

        protected override bool ProcessCmdKey(ref Message msg, Keys keyData)
        {
            if (keyData == Keys.Tab)
            {
                textBox1.Paste("\t");
                return true;
            }
            else if (keyData == (Keys.Shift | Keys.Tab))
            {
                textBox1.Paste("\xA0");
                return true;
            }
            return base.ProcessCmdKey(ref msg, keyData);
        }

    }
}

Huy Nguyen e.SuppressKeyPress = true;!

, Delete Backspace , ( Ctrl)

It seems to work for characters such as 𤽜, although it may not make much sense (is this character a whole word?)

0
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This is a simple solution that works for me.

private void MyTxtbox_Keypress(object sender, KeyPressEventArgs e)
{
    if (e.KeyChar == '\b')
    {
        e.Handled = true;

        return;
    }
}
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