TextBox with only numbers

Question

I need to create a TextBox with only numbers but I couldn't do. I have tried to put : InputScope = "Numbers" but this only work on Mobile. Also I have tried on TextChanging this:

private void textBox1_TextChanged(object sender, EventArgs e)
{
    if (System.Text.RegularExpressions.Regex.IsMatch(textBox1.Text, "[^0-9]"))
    {

        textBox1.Text = textBox1.Text.Remove(textBox1.Text.Length - 1);
    }
}

Answer 1

You can either prevent any non-numeric input whatsoever, or just filter out digits in the text.

Preventing non-digit input

Use the BeforeTextChanging event:

<TextBox BeforeTextChanging="TextBox_OnBeforeTextChanging" />

And now handle like this:

private void TextBox_OnBeforeTextChanging(TextBox sender,
                                          TextBoxBeforeTextChangingEventArgs args)
{
    args.Cancel = args.NewText.Any(c => !char.IsDigit(c));
}

This LINQ expression will return true and hence Cancel the text change in case it encounters any non-digit character in the input.

Filtering non-digit input

Use the TextChanging event:

<TextBox TextChanging="TextBox_OnTextChanging" /> 

And handle this way:

private void TextBox_OnTextChanging(TextBox sender, TextBoxTextChangingEventArgs args)
{
    //Save the position of the selection, to prevent the cursor to jump to the start
    int pos = sender.SelectionStart;
    sender.Text = new String(sender.Text.Where(char.IsDigit).ToArray());
    sender.SelectionStart = pos;
}

This LINQ query will filter out non-digit characters and create a new string only with the digits in the input.

It is preferable to use TextChanging and BeforeTextChanging, because TextChanged occurs too late, so the user would be confused by seeing characters temporarily display on the screen and immediately disappearing.

Answer 2

Based on the answer https://stackoverflow.com/a/52624310/13814517 for this question.

If you want to also allow input like 100.0 you might have a problem with the decimal point. so

1. enable the private OnBeforeTextChanging event on the textbox
2. in the handler:

private void TextBox_OnBeforeTextChanging(TextBox sender,
                                          TextBoxBeforeTextChangingEventArgs args)
{
    double tempDouble;
    args.Cancel  = !(double.TryParse(args.NewText, out tempDouble) | args.NewText == "");

}

Answer 3

Building on the accepted answer's solution for filtering out text, if you have to use the TextChanged event:

private void HexTextBox_TextChanged(object sender, EventArgs e)
{
    if (!(sender is TextBox txt))
        return;

    // Filter out any invalid chars that are typed/pasted and leave the cursor where it was (or reasonably close).
    int pos = txt.SelectionStart;
    txt.Text = string.Concat(txt.Text.Where(c => "0123456789abcdefABCDEF".IndexOf(c) != -1));
    txt.SelectionStart = pos;
}

This makes it so someone cannot type unwanted characters into the TextBox. And if they paste them in, they're ignored. E.g. for the above, if you tried to paste in "12#45^" you'd end up with "1245" in the TextBox.

Answer 4

You can do something else instead of TextBox.Text.Remove function which is Substring function and also you should fix it while they copy a series of characters which includes letters in the centre of the string:-

private void textBox1_TextChanged(object sender, EventArgs e)
{
    var txt = textBox1.Text;

        if (System.Text.RegularExpressions.Regex.IsMatch(txt, "[^0-9]"))
        {
            for (int i = 0; i < txt.Length; i++)
                if (!char.IsDigit(txt[i]))
                    if (i != txt.Length - 1)
                    {
                        //If he pasted a letter inclusive string which includes letters in the middle
                        //Remove the middle character or remove all text and request number as input
                        //I did the second way
                        textBox1.Text = "";
                        break;
                    }
                    else
                    {
                        //If he just typed a letter in the end of the text
                        textBox1.Text = txt.Substring(0, txt.Length - 1);
                        break;
                    }
        }
}

Answer 5

Here is an O(1) solution without string matching

    bool textCanceled = false;

    private void TextBox_KeyDown(object sender, KeyRoutedEventArgs e)
    {
        if (!Char.IsDigit((char)e.Key))
            textCanceled = true;
        else
            textCanceled = false;

    }

    private void TextBox_BeforeTextChanging(TextBox sender, TextBoxBeforeTextChangingEventArgs args)
    {
        args.Cancel = textCanceled;
    }

might have to handle backspace char as a special case