how to convert a databound zero double value to an empty string?

Question

Hi Guys,

I have this Payment object

public class Payment 
{
    public Guid Id { get; set; }
    public double Amount { get; set; }
}

which is data bound to a TextBox

<TextBox x:Name="_AmountTB" Text="{Binding Path=Amount, Mode=TwoWay}" />

I require that whenever the Amount is 0, then I don't show anything in the TextBox, how can this be done?

I am thinking some sort of converter, but I need someone to show me how to do this please?!

Thanks,

Voodoo

Answer 1

You can use a value converter for this but you don't need to. You can simply use the StringFormat of the Binding markup extension to specify a three-part custom numeric format string. It would look like this:

<TextBox Text="{Binding Path=Amount, StringFormat='0.00;-0.00;#'}" />

The semicolon in the string format tells .NET to use the first section to format positive numbers, the middle section to format negative numbers, and the last section to format zero values. The tricky part is getting an empty string for the zero part which I've used a pound (#) sign for. This format specifier shows a significant digit in its place but because the value will always be zero when that section is used, it results in an empty string.

Note that StringFormat requires Silverlight 4. If you're using Silverlight 3 you'll need a value converter. (You may want to make this handle errors more robustly...)

public class ZeroConverter : IValueConverter {

    public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
    {
        return String.Format(culture, "{0:0.00;-0.00;#}", value);
    }

    public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
    {
        string str = value as string;
        if (!String.IsNullOrEmpty(str)) {
            return System.Convert.ChangeType(str, targetType, culture);
        }
        return System.Convert.ChangeType(0, targetType, culture);
    }

}

XAML

<UserControl>
    <UserControl.Resources>
        <local:ZeroConverter x:Key="ZeroToEmpty" />
    </UserControl.Resources>
</UserControl>
<TextBox Text="{Binding Path=Amount, Converter={StaticResource ZeroToEmpty}}" />

Answer 2

public class BlankZeroConverter : IValueConverter
    {
        public object Convert(object value, Type targetType, object parameter,
                              System.Globalization.CultureInfo culture)
        {
            if (value == null)
                return null;

            if (value is double)
            {
                if ((double)value == 0)
                {
                    return string.Empty;
                }
                else
                    return value.ToString();

            }
            return string.Empty;
        }
   }