我正在尝试使用 C# 在 Windows Phone 8 上实现锁屏背景应用程序。这个想法是，当用户单击按钮时，会启动 PhotoChooserTask。当他从他的媒体库中挑选一张照片时，它会被复制到独立存储中，然后设置为锁屏背景。
问题是 Windows Phone 要求每个新的锁屏图片都有一个唯一的名称，因此解决方案必须如下：
- 用户从库中选择一张照片 2.1 如果当前锁屏图片EndsWith("_A.jpg")选择的照片被复制到隔离存储中作为photobackground_B.jpg并设置为锁屏背景 2.2。否则，如果当前锁屏图片不满足EndsWith("_A.jpg")条件，则将所选照片作为photobackground_A.jpg复制到隔离存储中，并设置为锁屏背景。
因此，实现了 A/B 切换逻辑，以便每个新的锁屏背景都有一个唯一的名称。
但是，我的代码不起作用。特别是以下行引发异常：
Windows.Phone.System.UserProfile.LockScreen.SetImageUri(new Uri("ms-appdata:///Local/photobackground_A.jpg", UriKind.Absolute));
似乎是什么问题？
PS我对编程完全陌生，所以我也非常感谢解释和适当的代码示例。谢谢！
using System;
using System.Collections.Generic;
using System.Linq;
using System.Net;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Navigation;
using Microsoft.Phone.Controls;
using Microsoft.Phone.Shell;
using Microsoft.Phone.Tasks;
using Day2Demo.Resources;
using System.Windows.Media;
using System.IO;
using System.IO.IsolatedStorage;
using Microsoft.Xna.Framework.Media;
namespace Day2Demo
{
public partial class MainPage : PhoneApplicationPage
{
PhotoChooserTask photoChooserTask;
// Constructor
public MainPage()
{
InitializeComponent();
// Sample code to localize the ApplicationBar
//BuildLocalizedApplicationBar();
}
private async void button1_Click(object sender, RoutedEventArgs e)
{
//check if current app provided the lock screen image
if (!Windows.Phone.System.UserProfile.LockScreenManager.IsProvidedByCurrentApplication)
{
//current image not set by current app ask permission
var permission = await Windows.Phone.System.UserProfile.LockScreenManager.RequestAccessAsync();
if (permission == Windows.Phone.System.UserProfile.LockScreenRequestResult.Denied)
{
//no permission granted so return without setting the lock screen image
return;
}
}
photoChooserTask = new PhotoChooserTask();
photoChooserTask.Completed += new EventHandler<PhotoResult>(photoChooserTask_Completed);
photoChooserTask.Show();
}
void photoChooserTask_Completed(object sender, PhotoResult e)
{
if (e.TaskResult == TaskResult.OK)
{
var currentImage = Windows.Phone.System.UserProfile.LockScreen.GetImageUri();
if (currentImage.ToString().EndsWith("_A.jpg"))
{
var contents = new byte[1024];
using (var store = IsolatedStorageFile.GetUserStoreForApplication())
{
using (var local = new IsolatedStorageFileStream("photobackground_B.jpg", FileMode.Create, store))
{
int bytes;
while ((bytes = e.ChosenPhoto.Read(contents, 0, contents.Length)) > 0)
{
local.Write(contents, 0, bytes);
}
}
Windows.Phone.System.UserProfile.LockScreen.SetImageUri(new Uri("ms-appdata:///Local/photobackground_B.jpg", UriKind.Absolute));
}
}
else
{
var contents = new byte[1024];
using (var store = IsolatedStorageFile.GetUserStoreForApplication())
{
using (var local = new IsolatedStorageFileStream("photobackground_A.jpg", FileMode.Create, store))
{
int bytes;
while ((bytes = e.ChosenPhoto.Read(contents, 0, contents.Length)) > 0)
{
local.Write(contents, 0, bytes);
}
}
Windows.Phone.System.UserProfile.LockScreen.SetImageUri(new Uri("ms-appdata:///Local/photobackground_A.jpg", UriKind.Absolute));
}
}
}
}
}
}