Unable to enter "." in a text box with decimal binding

Question

I have a textbox bound to a decimal value (property) and when I type the "3." it does not allow me to enter as it parses it back to 3 and hence I lose the ".". I tried the solutions like Delay/LostFocus etc but that did not work for me, from WPF validation rule preventing decimal entry in textbox?.

I have now written a IValueConverter class and I am obviously not doing it correctly. Here is the code:

[ValueConversion(typeof(decimal), typeof(string))]
public class DecimalToStringConverter : IValueConverter
{
    public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
    {
        //return Decimal.Parse(value.ToString());
        if (value == null) return Decimal.Zero;
        if (!(value is string)) return value;
        string s = (string)value;
        int dotCount = s.Count(f => f == '.');
        Decimal d;
        bool parseValid = Decimal.TryParse(s, out d);
        System.Text.RegularExpressions.Regex regex = new System.Text.RegularExpressions.Regex("^[-+]?([0-9]*?[.])?[0-9]*$");
        bool b = regex.IsMatch(s);
        if (dotCount == 1 && b)
        {
            return s;
        }
        return d;
    }

    public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
    {
        return value != null ? value.ToString() : "";
    }
}

XAML

<TextBox x:Name="ValueTextBox" Grid.Column="0" Grid.RowSpan="2" VerticalContentAlignment="Center" Text ="{Binding Value, Converter={StaticResource DecimalToStringConverter}}" PreviewTextInput="ValueTextBox_OnPreviewTextInput"  TextWrapping="Wrap" MouseWheel="ValueTextBox_MouseWheel" PreviewKeyDown="ValueTextBox_PreviewKeyDown" PreviewKeyUp="ValueTextBox_PreviewKeyUp" TextChanged="ValueTextBox_TextChanged" BorderThickness="1,1,0,1"/>

Please advise how I can correct this... Thanks

Answer 1

It's so annoying. You can't press "." but if you move back a character it lets you. It's because "21." is not a valid decimal.

For me I eventually gave up and made the field a string. There must be a better way but it got me past the issue for my use-case. You then also need to check to ensure it's a number etc, but at least the user experience is what they expect.