Restrict textbox to allow only decimal numbers

Question

I have a requirement to make a decimal textbox (Money textbox) which:

only allows numbers 0-9 (allow upper numpad keys 0-9 and right numpad keys 0-9);
allows only one dot which don't appear on start.

Valid:

0.5

1

1.5000

Invalid:

.5

5.500.55

Edit

my code is :

 private void floatTextBox_PreviewTextInput(object sender, TextCompositionEventArgs e)
    {
        e.Handled = !TextBoxValidation.AreAllValidDecimalChars(e.Text);
    }


  public static class TextBoxValidation
{
    public static bool AreAllValidDecimalChars(string str)
    {
        bool ret = false;
        int x = 0;
        foreach (char c in str)
        {
            x = (int)c;
        }
        if (x >= 48 && x <= 57 || x == 46)
        {
            ret = true;
        }
        return ret;
    }
}

Okay so you have a requirement. Please show us your effort. And explain to use why your effort is failing. — PhoenixReborn, Dec 03 '13 at 12:50
here is a similar question with an answer http://stackoverflow.com/questions/16914224/wpf-textbox-to-enter-decimal-values — blindmeis, Dec 03 '13 at 12:58
@Mussammil you have the validation outside of the loop. This will only check the last character. Also if it were correct, it will return true if ANY character is ok instead of ALL. — Bas, Dec 03 '13 at 13:10

Bas · Accepted Answer · 2013-12-03T13:11:33.617

If you want to allow copy and pasting as well you cannot do it with keyboard events. A TextBox has a TextChanged event which allows you to handle this event appropirately. If you want to block any input that is not a number or dot you could handle it like this:

private void TextBox_TextChanged(object sender, TextChangedEventArgs e)
{
    //get the textbox that fired the event
    var textBox = sender as TextBox;
    if (textBox == null) return;

    var text = textBox.Text;
    var output = new StringBuilder();
    //use this boolean to determine if the dot already exists
    //in the text so far.
    var dotEncountered = false;
    //loop through all of the text
    for (int i = 0; i < text.Length; i++)
    {
        var c = text[i];
        if (char.IsDigit(c))
        {
            //append any digit.
            output.Append(c);
        }
        else if (!dotEncountered && c == '.') 
        {
            //append the first dot encountered
            output.Append(c);
            dotEncountered = true;
        }
    }
    var newText = output.ToString();
    textBox.Text = newText;
    //set the caret to the end of text
    textBox.CaretIndex = newText.Length;
}

,thanks for ur response ,this will not solve my requirement 2 (dot never come as first character eg: .5 is invalid instead 0.5 is valid) how to accomplish this too — Mussammil, Dec 04 '13 at 04:34

score -1 · Answer 2 · answered Dec 03 '13 at 12:58

-1

You can achieve your goal by simply implementing two event handlers on a TextBox:

TextCompositionEventHandler textBox_PreviewTextInput = 
    new TextCompositionEventHandler((s, e) => e.Handled = !e.Text.All(
    c => Char.IsNumber(c) || c == '.'));
KeyEventHandler textBox_PreviewKeyDown = new KeyEventHandler(
    (s, e) => e.Handled = e.Key == Key.Space);

textBox.PreviewTextInput += textBox_PreviewTextInput;
textBox.PreviewKeyDown += textBox_PreviewKeyDown;

answered Dec 03 '13 at 12:58

Sheridan

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Try pasting 'Hello World!' into the textbox. – Bas Dec 03 '13 at 13:08
+1 Thanks for pointing that out @BasBrekelmans... I've been using this for years and never noticed that. I would have fixed that using the `TextChanged` event, but not wanting to copy your answer, I'll just keep the -1. – Sheridan Dec 03 '13 at 13:28

Restrict textbox to allow only decimal numbers

2 Answers2