ImageSourceConverter error for Source=null

Question

I'm binding the Source property of an Image to a string. This string may be null in which case I just don't want to display an Image. However, I'm getting the following in my Debug output:

System.Windows.Data Error: 23 : Cannot convert '<null>' from type '<null>' to type 'System.Windows.Media.ImageSource' for 'en-AU' culture with default conversions; consider using Converter property of Binding. NotSupportedException:'System.NotSupportedException: ImageSourceConverter cannot convert from (null). at System.ComponentModel.TypeConverter.GetConvertFromException(Object value) at System.Windows.Media.ImageSourceConverter.ConvertFrom(ITypeDescriptorContext context, CultureInfo culture, Object value) at MS.Internal.Data.DefaultValueConverter.ConvertHelper(Object o, Type destinationType, DependencyObject targetElement, CultureInfo culture, Boolean isForward)'

I'd prefer if this wasn't displayed as it's just noise - is there any way to suppress it?

Answer 1

@AresAvatar is right in suggesting you use a ValueConverter, but that implementation does not help the situation. This does:

public class NullImageConverter :IValueConverter {     public object Convert(object value, Type targetType, object parameter, CultureInfo culture)     {         if (value == null)             return DependencyProperty.UnsetValue;         return value;     }      public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)     {         // According to https://msdn.microsoft.com/en-us/library/system.windows.data.ivalueconverter.convertback(v=vs.110).aspx#Anchor_1         // (kudos Scott Chamberlain), if you do not support a conversion          // back you should return a Binding.DoNothing or a          // DependencyProperty.UnsetValue         return Binding.DoNothing;         // Original code:         // throw new NotImplementedException();     } } 

Returning DependencyProperty.UnsetValue also addresses the performance issues from throwing (and ignoring) all those exceptions. Returning a new BitmapSource(uri) would also get rid of the exceptions, but there is still a performance hit (and it isn't necessary).

Of course, you'll also need the plumbing:

In resources:

<local:NullImageConverter x:Key="nullImageConverter"/> 

Your image:

<Image Source="{Binding Path=ImagePath, Converter={StaticResource nullImageConverter}}"/> 

Answer 2

I used Pat's ValueConverter technique and it worked great. I also tried the TargetNullValue technique, by flobodob from here, and it also works great. It's easier and cleaner.

<Image Source="{Binding LogoPath, TargetNullValue={x:Null}}" /> 

TargetNullValue is simpler, and requires no converter.