Detect whether WPF resource exists, based on URI

Question

Given a pack:// URI, what's the best way to tell whether a compiled resource (e.g. a PNG image, compiled with a Build Action of "Resource") actually exists at that URI?

After some stumbling around, I came up with this code, which works but is clumsy:

private static bool CanLoadResource(Uri uri)
{
    try
    {
        Application.GetResourceStream(uri);
        return true;
    }
    catch (IOException)
    {
        return false;
    }
}

(Note that the Application.GetResources documentation is wrong -- it throws an exception if the resource isn't found, rather than returning null like the docs incorrectly state.)

I don't like catching exceptions to detect an expected (non-exceptional) result. And besides, I don't actually want to load the stream, I just want to know whether it exists.

Is there a better way to do this, perhaps with lower-level resource APIs -- ideally without actually loading the stream and without catching an exception?

Answer 1

Application.GetResourceStream doesn't throw an exception if the resource is not found, it just returns null.

From MSDN :

Return Value

Type: System.Windows.Resources.StreamResourceInfo

A StreamResourceInfo that contains a resource stream for resource data file that is located at the specified Uri. If the resource located at the specified Uri is not found, null is returned.

So you can just do that :

private static bool CanLoadResource(Uri uri)
{
    return Application.GetResourceStream(uri) != null;
}

Answer 2

I've found a solution that I'm using which doesn't work directly with a pack Uri but instead looks up a resource by it's resource path. That being said, this example could be modified pretty easily to support a pack URI instead by just tacking on the resource path to the end of a uri which uses the Assembly to formulate the base part of the URI.

public static bool ResourceExists(string resourcePath)
{
    var assembly = Assembly.GetExecutingAssembly();

    return ResourceExists(assembly, resourcePath);
}

public static bool ResourceExists(Assembly assembly, string resourcePath)
{
    return GetResourcePaths(assembly)
        .Contains(resourcePath);
}

public static IEnumerable<object> GetResourcePaths(Assembly assembly)
{
    var culture = System.Threading.Thread.CurrentThread.CurrentCulture;
    var resourceName = assembly.GetName().Name + ".g";
    var resourceManager = new ResourceManager(resourceName, assembly);

    try
    {
        var resourceSet = resourceManager.GetResourceSet(culture, true, true);

        foreach(System.Collections.DictionaryEntry resource in resourceSet)
        {
            yield return resource.Key;
        }
    }
    finally
    {
        resourceManager.ReleaseAllResources();
    }
}