通过Windows Phone 8上的代码解决XAML绑定

Question

I have a converter that provides a default value for empty strings. Apparently you can't add a binding to the ConverterParameter so I add a property to the converter, which I bind to instead.

However, the value I'm getting back for the default property is a string of "System.Windows.Data.Binding" instead of my value.

How do I resolve this binding in code so I can return the real localized string I want?

Here's my converter class (based on answer https://stackoverflow.com/a/15567799/250254 ):

public class DefaultForNullOrWhiteSpaceStringConverter : IValueConverter
{
    public object Default { set; get; }

    public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
    {
        if (!string.IsNullOrWhiteSpace((string)value))
        {
            return value;
        }
        else
        {
            if (parameter != null)
            {
                return parameter;
            }
            else
            {
                return this.Default;
            }
        }
    }

    public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
    {
        throw new NotSupportedException();
    }

}

And my XAML:

<phone:PhoneApplicationPage.Resources>
    <tc:DefaultForNullOrWhiteSpaceStringConverter x:Key="WaypointNameConverter"
        Default="{Binding Path=LocalizedResources.Waypoint_NoName, Mode=OneTime, Source={StaticResource LocalizedStrings}}" />
</phone:PhoneApplicationPage.Resources>

<TextBlock Text="{Binding Name, Converter={StaticResource WaypointNameConverter}}" />

Any ideas?

Answer 1

You should be able to accomplish this by inheriting from DependencyObject and changing your Default property to be a DependencyProperty .

public class DefaultForNullOrWhiteSpaceStringConverter : DependencyObject, IValueConverter
{
    public string DefaultValue
    {
        get { return (string)GetValue(DefaultValueProperty); }
        set { SetValue(DefaultValueProperty, value); }
    }

    // Using a DependencyProperty as the backing store for DefaultValue.  This enables animation, styling, binding, etc...
    public static readonly DependencyProperty DefaultValueProperty =
        DependencyProperty.Register("DefaultValue", typeof(string), 
        typeof(DefaultForNullOrWhiteSpaceStringConverter), new PropertyMetadata(null));
...
...

Answer 2

For now I've resolved the issue by inheriting from my converter and setting the localized string in the constructor. However, I feel there's must be a more elegant solution to my problem that allows the base converter to be used directly.

public class WaypointNameConverter : DefaultForNullOrWhiteSpaceStringConverter
{
    public WaypointNameConverter()
    {
        base.Default = Resources.AppResources.Waypoint_NoName;
    }
}