page.cs

  public partial class FullscreenPage : PhoneApplicationPage
    {

        Item item;

        public FullscreenPage()
        {
            InitializeComponent();

        }

        protected override void OnNavigatedTo(System.Windows.Navigation.NavigationEventArgs e)
        {
            base.OnNavigatedTo(e);

            string objectId;
    
            NavigationContext.QueryString.TryGetValue("ObjectId", out objectId);

            var itemsDB = new ItemsContext(ItemsContext.DBConnectionString);

            item = (from r in itemsDB.artifacts where r.Id.Equals(objectId) select r).First();

        }
    }

page.xaml

    <ContentControl ContentTemplate="{Binding}">
        <testapp:FullscreenTypeSelector>
            <testapp:FullscreenTypeSelector.ImageTemplate>
                <ControlTemplate>
                    <StackPanel>
                        <Image Name="Image" Source="{Binding PayloadUri}"/>
                    </StackPanel>
                </ControlTemplate>
            </testapp:FullscreenTypeSelector.ImageTemplate>
            <testapp:FullscreenTypeSelector.TextTemplate>
                <ControlTemplate>
                    <StackPanel>
                        <TextBlock Name="MimeText" Text="{Binding Mime}"/>
                    </StackPanel>
                </ControlTemplate>
            </testapp:FullscreenTypeSelector.ImageTemplate>
        </testapp:FullscreenTypeSelector>
    </ContentControl>

selector.cs

    public class FullscreenTypeSelector : ContentControl
    {

        public ControlTemplate ImageTemplate
        {
            get;
            set;
        }

        public ControlTemplate TextTemplate
        {
            get;
            set;
        }

        //Use ContentControl as a container and bind ContentTemplate property to your DataTemplateSelector.

        ControlTemplate SelectTemplate(object item, DependencyObject container)
        {
            Item foodItem = item as Item;
            if (foodItem != null)
            {
                if (foodItem.Mime == "note")
                {
                    return TextTemplate;
                }
                else 
                {
                    return ImageTemplate;
                }
              
            }
            return null;
        }
    }