WPF Image异步加载控件

<ImageLoadingControl:ImageLoadingControl HorizontalAlignment="Left" Height="200" Margin="30,68,0,0" VerticalAlignment="Top" Width="200"  Source="{Binding ImageUrl1}"/>
<ImageLoadingControl:ImageLoadingControl HorizontalAlignment="Left" Height="200" Margin="303,68,0,0" VerticalAlignment="Top" Width="200" Source="{Binding ImageUrl2}"/>
<ImageLoadingControl:ImageLoadingControl HorizontalAlignment="Left" Height="200" Margin="556,68,0,0" VerticalAlignment="Top" Width="200" Source="{Binding ImageUrl3}"/>

private void button_Click(object sender, RoutedEventArgs e)
{
    ImageUrl1 = @"https://pixabay.com/static/uploads/photo/2016/02/09/13/45/rock-carvings-1189288_960_720.jpg";
    ImageUrl2 = @"https://pixabay.com/static/uploads/photo/2016/02/14/14/32/construction-1199586_960_720.jpg";
    ImageUrl3 = @"c:\test.jpg";
}