Windows 8 - TextBox that only accepts numbers goes wrong

Question

here is my TextBox written in C# with Key Down event handler

private void TextBox_KeyDown(object sender, Windows.UI.Xaml.Input.KeyRoutedEventArgs e)
{
        //ONLY ACCEPTS NUMBERS
        char c = Convert.ToChar(e.Key);
        if (!c.Equals('0') && !c.Equals('1') && !c.Equals('2') && !c.Equals('3') && !c.Equals('4') &&
            !c.Equals('5') && !c.Equals('6') && !c.Equals('7') && !c.Equals('8') && !c.Equals('9'))
        {
            e.Handled = true;
        }
}

it does works preventing letters from a to z. However, if I enter symbols like !@#$%^&*()_+, it stills accept them. What am I missing?

Answer 1

You can use Char.IsDigit

e. Handled = !Char.IsDigit(c);

But this won't help you much in case of copy\pasting.

Also check related question on the right. For example Create WPF TextBox that accepts only numbers

---

UPDATE

For letters only try

e.Handled = Char.IsLetter(c);

Answer 2

There is no reliable way to handle this on the key down or key up events because for some odd reason shift 4 which is the $ sign returns 4 not the key value.

The best workaround is to catch the value before it's used and check it is numeric then alert the user.

var IsNumeric = new System.Text.RegularExpressions.Regex("^[0-9]*$");
        if (!IsNumeric.IsMatch(edtPort.Text))
        {
            showMessage("Port number must be number", "Input Error");
            return;
        }

In no way ideal but better that trying to teach your users that the dollar sign is now a number!

Answer 3

Try this code. But sometimes you see char that you pressed and it is removed immediately. Not the best solution but sufficient

private void TextBox_OnTextChanged(object sender, TextChangedEventArgs e)
{
    var textBox = sender as TextBox;
    if (textBox == null)
        return;

    if (textBox.Text.Length == 0) return;

    var text = textBox.Text;

    int result;
    var isValid = int.TryParse(text, out result);
    if (isValid) return;


    var selectionStart = textBox.SelectionStart;
    var resultString = new string(text.Where(char.IsDigit).ToArray());
    var lengthDiff = textBox.Text.Length - resultString.Length;

    textBox.Text = resultString;
    textBox.SelectionStart = selectionStart - lengthDiff;
}

Answer 4

this might help, this is what I used.

    private void txtBoxBA_KeyDown(object sender, KeyRoutedEventArgs e)
    {
        // only allow 0-9 and "."
        e.Handled = !((e.Key.GetHashCode() >= 48 && e.Key.GetHashCode() <= 57));

        // check if "." is already there in box.
        if (e.Key.GetHashCode() == 190)
            e.Handled = (sender as TextBox).Text.Contains(".");
    }