Xamarin XAML绑定到listview变量

Question

如何制作将ThumbBlobURl和BlobURL绑定到ImageName的ImageSource网址？

    <ListView 
            x:Name="listView"
            SeparatorVisibility="Default"
            ItemTapped="OnItemTapped"
            IsPullToRefreshEnabled="true" Refreshing="OnRefresh"
          >

        <ListView.ItemTemplate>
            <DataTemplate>

                <ViewCell>
                    <StackLayout HorizontalOptions="Start" Orientation="Horizontal">
                        <Image Source="{Binding ImageName, StringFormat = ThumbBlobURL + '{0}'}" HorizontalOptions="Start" HeightRequest = "64"/>
                        <Image Source="{Binding ImageName, StringFormat = BlobURL + '{0}'}" HorizontalOptions="Start" HeightRequest = "64"/>