我在 Windows 8 C# 应用程序中有以下代码,它从服务器获取图像并存储它:
private async Task httpFetcher()
{
HttpClient httpClient = new HttpClient();
HttpRequestMessage request = new HttpRequestMessage(
HttpMethod.Get, "http://www.example.com/fakeImageRotator.php"); // FOR EXAMPLE
HttpResponseMessage response = await httpClient.SendAsync(request,
HttpCompletionOption.ResponseHeadersRead);
Uri imageUri;
BitmapImage image = null;
try
{
var imageFile = await ApplicationData.Current.LocalFolder.CreateFileAsync(
"test.png", CreationCollisionOption.ReplaceExisting);
var fs = await imageFile.OpenAsync(FileAccessMode.ReadWrite);
DataWriter writer = new DataWriter(fs.GetOutputStreamAt(0));
writer.WriteBytes(await response.Content.ReadAsByteArrayAsync());
await writer.StoreAsync();
writer.DetachStream();
await fs.FlushAsync();
writer.Dispose();
if (Uri.TryCreate(imageFile.Path, UriKind.RelativeOrAbsolute, out imageUri))
{
image = new BitmapImage(imageUri);
}
}
catch (Exception e)
{
return;
}
image1.Source = image;
}
看来我在这一特定行上随机出现错误:
var imageFile = await ApplicationData.Current.LocalFolder.CreateFileAsync(
"test.png", CreationCollisionOption.ReplaceExisting);
它并不总是发生,所以我不确定如何查明问题。所有错误详细信息都在这里:
UnauthorizedAccessException 被捕获
访问被拒绝。 (HRESULT 异常:0x80070005
(E_ACCESSDENIED)) 在
System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(任务
任务)在
System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(任务
任务)在 System.Runtime.CompilerServices.TaskAwaiter`1.GetResult()
在 TestApp.MainPage.d__4.MoveNext() 中
d:\TestApp\TestApp\MainPage.xaml.cs:第 86 行
更新 - “访问被拒绝”错误是由多种原因引起的。
第一个原因与图像的下载有关。下载代码中的某些内容似乎使文件保持打开状态。我简化了下面的下载代码。
第二个原因与BitmapImage
保持打开文件的对象。请参阅这篇文章了解更多信息:删除先前在 WinRT 的 DataTemplate 中使用的图像文件时访问被拒绝 http://social.msdn.microsoft.com/Forums/en-US/winappswithcsharp/thread/ece23cfd-996d-41c5-8add-188db000c2d0/
解决第二个问题的一种方法是使用stream
代替Uri
初始化BitmapImage
.
这是一个适合我的版本(您的原始代码也在这里,但已注释掉):
var imageFile = await ApplicationData.Current.LocalFolder.CreateFileAsync(
"test.png", CreationCollisionOption.ReplaceExisting);
/*
var fs = await imageFile.OpenAsync(FileAccessMode.ReadWrite);
DataWriter writer = new DataWriter(fs.GetOutputStreamAt(0));
writer.WriteBytes(await response.Content.ReadAsByteArrayAsync());
await writer.StoreAsync();
writer.DetachStream();
await fs.FlushAsync();
writer.Dispose();
if (Uri.TryCreate(imageFile.Path, UriKind.RelativeOrAbsolute, out imageUri))
{
image = new BitmapImage(imageUri);
}
*/
var fs = await imageFile.OpenStreamForWriteAsync();
await response.Content.CopyToAsync(fs);
await fs.FlushAsync();
// you may want to have this Dispose as part of a
// finally block (try/ catch/ finally)
fs.Dispose();
var bs = await imageFile.OpenAsync(Windows.Storage.FileAccessMode.Read);
image = new BitmapImage();
image.SetSource(bs);
...
image1.Source = image;
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