显示图片从URL与Xamarin.Forms

我使用这个代码来显示来自URL的图像

.xaml

<?xml version="1.0" encoding="UTF-8"?>
<ContentPage xmlns="http://xamarin.com/schemas/2014/forms" xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml" x:Class="LandAHand.VolunteerView">
    <ContentPage.Content>
         <AbsoluteLayout BackgroundColor="Maroon">
             <Image x:Name="backgroundImage" AbsoluteLayout.LayoutBounds="0,0,1,1" AbsoluteLayout.LayoutFlags="All" HorizontalOptions="FillAndExpand" VerticalOptions="FillAndExpand" Aspect="AspectFill" />
         </AbsoluteLayout>
    </ContentPage.Content>
</ContentPage>

cs

using System;
using System.Collections.Generic;
using Xamarin.Forms;
namespace LandAHand
{
    public partial class VolunteerView : ContentPage
    {
        public VolunteerView()
        {
            InitializeComponent();
            backgroundImage.Source = new UriImageSource
            {
                Uri = new Uri("https://s9.postimg.org/aq1jt3fu7/handshake_87122244_std.jpg"),
                CachingEnabled = true,
                CacheValidity = new TimeSpan(5, 0, 0, 0)
            };
        }
    }
}

此代码可以在iOS上成功运行，但不能在Android上运行。