C#•3w ago

Decimal in clamped TextBox

I'm implementing a numerical TextBox that may clamp entered values between a min and max value. I achieved this by overriding the MetaData for the Text property with a TwoWay binding by default and an OnTextChanged handler. One of the hurdles along the way was partially entered values such as -, 0., 1.3, etc. I overcame this with a regex. The issue I have is that I'm unable to enter a decimal into the TextBox despite being allowed by the regex ^(-?\d+\.|-0?)$. Here is my on changed handler.

private static void OnTextChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
{
    var s = (string)e.NewValue;
    var regex = new Regex(@"^(-?\d+\.|-0?)$");
    if (string.IsNullOrEmpty(s) || regex.Match(s).Success)
        return;

    if (double.TryParse((string)e.NewValue, out var oldValue))
    {
        if (!(bool)d.GetValue(EnforceRangeProperty))
            return;

        var min = (double)d.GetValue(MinProperty);
        var max = (double)d.GetValue(MaxProperty);

        var newValue = Math.Max(min, oldValue);
        newValue = Math.Min(max, newValue);

        // ReSharper disable once CompareOfFloatsByEqualityOperator
        if (newValue == oldValue)
            return;

        d.SetValue(TextProperty, newValue.ToString(CultureInfo.InvariantCulture));
        return;
    }

    // If we can't parse the text, revert to the old value.
    d.SetValue(TextProperty, (string)e.OldValue);
}

private static void OnTextChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
{
    var s = (string)e.NewValue;
    var regex = new Regex(@"^(-?\d+\.|-0?)$");
    if (string.IsNullOrEmpty(s) || regex.Match(s).Success)
        return;

    if (double.TryParse((string)e.NewValue, out var oldValue))
    {
        if (!(bool)d.GetValue(EnforceRangeProperty))
            return;

        var min = (double)d.GetValue(MinProperty);
        var max = (double)d.GetValue(MaxProperty);

        var newValue = Math.Max(min, oldValue);
        newValue = Math.Min(max, newValue);

        // ReSharper disable once CompareOfFloatsByEqualityOperator
        if (newValue == oldValue)
            return;

        d.SetValue(TextProperty, newValue.ToString(CultureInfo.InvariantCulture));
        return;
    }

    // If we can't parse the text, revert to the old value.
    d.SetValue(TextProperty, (string)e.OldValue);
}

What changes can I make to allow for the entry of a decimal point? Edit: I've also realised that I cannot enter -0, subsequently -0.

7 Replies

HtmlCompiler•3w ago

(pls don't create a regex everytime the method is called 😐 im not sure i would even use a regex here)

SamuelOP•3w ago

I only included it in the method for clarity I'm open to alternatives to a regex but please keep responses related to the asked question

HtmlCompiler•3w ago

to me double.TryParse would be enough (although i would explicitly pass the culture) if you had put var regex in a comment i would have understood it was not initialized in this context also code is exiting on regex.Success, is it missing a == false

SamuelOP•3w ago

TryParse is not sufficient. For example, if you user starts to enter a negative number, the parsing will fail, and will be reverted to an earlier value. Also, parsing values such as 0., -1. or 123. will parse successfully and remove the decimal

HtmlCompiler•3w ago

ok still, what about this:

-    if (string.IsNullOrEmpty(s) || regex.Match(s).Success)
+    if (string.IsNullOrEmpty(s) || regex.Match(s).Success == false)
        return;

-    if (string.IsNullOrEmpty(s) || regex.Match(s).Success)
+    if (string.IsNullOrEmpty(s) || regex.Match(s).Success == false)
        return;

SamuelOP•3w ago

Then no valid entries would be parsed

HtmlCompiler•3w ago

haha my fault i misread the regex, im sick today so regex is not blocking 1.23 at this point the next [possible] culprit is double.TryParse and the culture question i don't know where you are, but this: 1.23 smells of invariant culture

Gaming

Programming

Decimal in clamped TextBox