Wpf – Handling null when binding to an Image in XAML

bindingwpf

I have an Image element in XAML. I bind the Source property to a string property in my ViewModel. However, sometimes the value is null and then I get errors in the debug window.

I read here: ImageSourceConverter error for Source=null that I could make a converter to return DependencyProperty.UnsetValue if the value is null.

Now I'm wondering if it is possible to do it directly in XAML? Perhaps by using a FallbackValue?
I have tried some variants but with no luck.

This is my Image element in XAML:

<Image Name="img" Source="{Binding Path=CurrentImageSource}" Stretch="None" />

And CurrentImageSource is just a string property on the DataContext.

The error message is:
System.Windows.Data Error: 23 :

Cannot convert '' from type '' to type
'System.Windows.Media.ImageSource' for 'sv-SE' culture with default
conversions; consider using Converter property of Binding.
NotSupportedException:'System.NotSupportedException:
ImageSourceConverter cannot convert from (null).

Best Answer

I used x:Null with TargetNullValue, that way you get an easy blank image...

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

That way you don't need to mess around with Triggers or BitmapImages as static resources.

Related Solutions

Wpf – Binding to static property

If the binding needs to be two-way, you must supply a path.

There's a trick to do two-way binding on a static property, provided the class is not static : declare a dummy instance of the class in the resources, and use it as the source of the binding.

<Window.Resources>
    <local:VersionManager x:Key="versionManager"/>
</Window.Resources>
...

<TextBox Text="{Binding Source={StaticResource versionManager}, Path=FilterString}"/>

C# – Solution to binding errors thrown by setting Image.Source to a binding to null. (suppression?)

I ran into the same problem trying to use a string URI (rather than a Stream). I resolved the issue by setting up a property on my view model of type ImageSource, which is the type of the Source property on Image, and binding Source to that property. This gets any automatic conversion out of the mix. Within the new property, handle the null case, then defer to the standard ImageSourceConverter. In your case, I think this would look something like this:

Code:

public const string ImageStreamPropertyName = "ImageStream";

private Stream _imageStream = null;

public Stream ImageStream
{
    get
    {
        return _imageStream;
    }

    set
    {
        if (_imageStream == value)
        {
            return;
        }
        _imageStream = value;

        RaisePropertyChanged(ImageStreamPropertyName);
        // Raise for ImageSource too since it changes with ImageStream
        RaisePropertyChanged("ImageSource");
    }
}

public ImageSource ImageSource
{
    get
    {
        if (ImageStream == null)
            return null;

        return (ImageSource)new ImageSourceConverter().ConvertFrom(ImageStream);
    }
}

XAML:

    <Image.Source>
        <Binding Path="ImageSource" />
    </Image.Source>

Best Answer

Related Solutions

Wpf – Binding to static property

C# – Solution to binding errors thrown by setting Image.Source to a binding to null. (suppression?)

Related Topic