How to use Attached property within a style?

Question

I have created an Image within a ButtonStyle. Now I have created an Attached Property so that I can set the Source for that Image. Should be straight forward but I am stuck with it.

This is my shortened ButtonStyle:

<Style x:Key="ToolBarButtonStyle"
        TargetType="Button">
    ...
    <Image x:Name="toolbarImage"
            Source="{TemplateBinding PrismExt:ImageSourceAttachable:ImageSource}"
            Width="48"
            Height="48" />
    ...
</Style>

And this is the attached property definition, Note that I have no idea how to fix the callback, as the dependencyproperty seems to be the button instead of the image. And Button doesn't expose my Image within its style. Its tricky.

namespace SalesContactManagement.Infrastructure.PrismExt
{
    public class ImgSourceAttachable
    {
        public static void SetImgSource(DependencyObject obj, string imgSource)
        {
            obj.SetValue(ImgSourceProperty, imgSource);
        }

        public static string GetImgSource(DependencyObject obj)
        {
            return obj.GetValue(ImgSourceProperty).ToString();
        }

        // Using a DependencyProperty as the backing store for MyProperty.  This enables animation, styling, binding, etc...
        public static readonly DependencyProperty ImgSourceProperty =
            DependencyProperty.RegisterAttached("ImgSource", typeof(string), typeof(ImgSourceAttachable), new PropertyMetadata(Callback));

        private static void Callback(DependencyObject d, DependencyPropertyChangedEventArgs e)
        {
            //((Button)d).Source = new BitmapImage(new Uri(Application.Current.Host.Source, e.NewValue.ToString()));
        }
    }
}

This is how I set the image source within XAML:

<Button PrismExt:ImgSourceAttachable.ImgSource="./Images/New.png"
        Style="{StaticResource ToolBarButtonStyle}" />

Any ideas please? Many Thanks,

Answer 1

Here is how you can set your attached property in a style

<Style x:Key="ToolBarButtonStyle" TargetType="Button">
    <Setter Property="PrismExt:ImgSourceAttachable.ImgSource"
            Value="./Images/New.png"/>
    <!--...-->
</Style>

When binding to attached properties then the Path should be within parentheses so try to use RelativeSource Binding with TemplatedParent instead

<Setter Property="Template">
    <Setter.Value>
        <ControlTemplate TargetType="Button">
            <Image x:Name="toolbarImage"
                    Source="{Binding RelativeSource={RelativeSource TemplatedParent},
                                    Path=(PrismExt:ImgSourceAttachable.ImgSource)}"
                    Width="48"
                    Height="48">
            </Image>
        </ControlTemplate>
    </Setter.Value>
</Setter>

Edit: The above code works in WPF, in Silverlight the Image shows in runtime but it fails in the designer with an exception. You can use the following code in the PropertyChangedCallback to get the Image as a workaround

private static void Callback(DependencyObject d, DependencyPropertyChangedEventArgs e)
{
    Button button = d as Button;
    Image image = GetVisualChild<Image>(button);
    if (image == null)
    {
        RoutedEventHandler loadedEventHandler = null;
        loadedEventHandler = (object sender, RoutedEventArgs ea) =>
        {
            button.Loaded -= loadedEventHandler;
            button.ApplyTemplate();
            image = GetVisualChild<Image>(button);
            // Here you can use the image
        };
        button.Loaded += loadedEventHandler;
    }
    else
    {
        // Here you can use the image
    }
}
private static T GetVisualChild<T>(DependencyObject parent) where T : DependencyObject
{
    T child = default(T);

    int numVisuals = VisualTreeHelper.GetChildrenCount(parent);
    for (int i = 0; i < numVisuals; i++)
    {
        DependencyObject v = (DependencyObject)VisualTreeHelper.GetChild(parent, i);
        child = v as T;
        if (child == null)
        {
            child = GetVisualChild<T>(v);
        }
        if (child != null)
        {
            break;
        }
    }
    return child;
}