如何在MultiBinding中保持原始值不变

Question

I have the following multi-binding for my TextBlock

<Multibinding Converter="{StaticResource myconv}">
 <Binding Path="Property1" />
 <Binding Path="Property2" />
 <Binding Path="Property3" />
</Multibinding>

Here is my converter code

public class PropertiesSelectorConverter : IMultiValueConverter
{
    public object Convert(object[] values, Type targetType, object parameter, System.Globalization.CultureInfo culture)
    {
        return values.Where(v => v != null).FirstOrDefault();

    }

    public object[] ConvertBack(object value, Type[] targetTypes, object parameter, System.Globalization.CultureInfo culture)
    {
        throw new NotImplementedException();
    }
}

Problem Now what I would like to do here is when all of the Property1 , Property2 and Property3 are null, I want TextBlock to retain its original value. How do I accomplish this ?

Answer 1

You can use the special value of Binding called Binding.DoNothing :

public object Convert(object[] values, Type targetType, object parameter, System.Globalization.CultureInfo culture)
{
    var value = values.Where(v => v != null).FirstOrDefault();
    return value == null ? Binding.DoNothing : value;
}