Question

I’m developing a map application in Silverlight. I have a type Polygon, containing the coordinates of a polygon together with a string containing the name of Brush resource loaded into the application. I’m binding this object directly to a template for drawing polygons. This template has a Fill-propery of type System.Windows.Media.Brush.

My goal is to let the xaml-parser do the lookup of the resource, considering I only have the name of the Brush and not the resource itself.

In Silverlight I want to achieve something similar to what Pedro Sampaio is showing in WPF in this blog post: http://www.e-pedro.com/2009/06/using-data-binding-with-static-resources-in-wpf/. He has created a BindableStaticResource inheriting the StaticResourceExtension-type. Then he can do the binding like this:

<Polygon Fill="{BindableStaticResource {Binding NameOfFillResource}}" />

Very elegant! But it appears that this is not an option in Silverlight since there are no MarkupExtension-type to subtype. I’m fairly new to Silverlight, and can’t really think of a good, reusable way of implementing this.

Thanks!
HaraldV

Answer 1

Your are correct there is no way create your own markup extensions for silverlight.

I solve this sort of problem with a value converter. I’ve answered this sort of thing so often I ended up blogging it here.

With the source for StringToObjectConverter in you project your can place an instance of the converter in your resources somewhere:-

        <local:StringToObjectConverter x:Key="StatusToBrush">
            <ResourceDictionary>
                <SolidColorBrush Color="Red" x:Key="Overdue" />
                <SolidColorBrush Color="Orange" x:Key="Urgent" />
                <SolidColorBrush Color="Silver" x:Key="__default__" /> 
            </ResourceDictionary>
        </local:StringToObjectConverter>

then your binding will look like:-

<Polygon Fill="{Binding NameOfFillResource, Converter={StaticResource StatusToBrush}}" />