GetContent.cs

var view = item.Content;
if (view.Contains(StandardDataFormats.Bitmap))
{
    var bitmapReference = await view.GetBitmapAsync();
    if (bitmapReference != null)
    {
        var bitmap = new BitmapImage();
        await bitmap.SetSourceAsync(await bitmapReference.OpenReadAsync());
        viewer.ContentGrid.Children.Add(new Image() { Width = 300, Height = 300, Stretch = Stretch.None, Source = bitmap });
    }
}
else if (view.Contains(StandardDataFormats.Text))
{
    var text = await view.GetTextAsync();
    if (text != null)
    {
        viewer.ContentGrid.Children.Add(new TextBlock() { Text = text });
    }
}