Question

I have a Textblock which Text attribute is binding to a DateTime? type data, and I want to show something when the DateTime? data is null.

The code below works great.

  < TextBlock Text="{Binding DueDate, TargetNullValue='wow,It's null'}"/>

But what about if I want to bind a Localizedstring to the TargetNullValue?
The Code below not work 🙁
How to?

  < TextBlock Text="{Binding DueDate, TargetNullValue={Binding LocalStrings.bt_help_Title1, Source={StaticResource LocalizedResources}} }"/>

Answer 1

I don’t see any way to do that with TargetNullValue. As a workaround, you can try using a converter:

public class NullValueConverter : IValueConverter
{
    public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
    {
        if (value != null)
        {
            return value;
        }

        var resourceName = (string)parameter;

        return AppResources.ResourceManager.GetString(resourceName);
    }

    public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
    {
        throw new NotImplementedException();
    }
}

Then add it to the resources of your page:

<phone:PhoneApplicationPage.Resources>
    <local:NullValueConverter x:Key="NullValueConverter" />
</phone:PhoneApplicationPage.Resources>

Finally, use it instead of TargetNullValue:

<TextBlock Text="{Binding DueDate, Converter={StaticResource NullValueConverter}, ConverterParameter=bt_help_Title1}" />