string path = string.Format("../ClientBin/{0}.xap", "catalogTesting");
void MainPage_Loaded(object sender, RoutedEventArgs e)
    {
        LoadXapFile("catalogTesting");
    }

 private void LoadXapFile(string name)
    {
        var catalog = new AggregateCatalog();
        try
        {
            CompositionHost.Initialize(new DeploymentCatalog(), catalog);
            CompositionInitializer.SatisfyImports(this);
        }
        catch (Exception)
        {

        }

        catalog.Catalogs.Add(CreateCatalog(name));
    }

 private DeploymentCatalog CreateCatalog(string uri)
    {
        DeploymentCatalog catalog;
        catalog = new DeploymentCatalog(path + uri + @".xap");
        catalog.DownloadCompleted += (e, sa) =>
        {

        };
        catalog.DownloadAsync();
        return catalog;

    }