将包含图像的流保存到 Windows Phone 8 上的本地文件夹 [英] Saving a stream containing an image to Local folder on Windows Phone 8

问题描述

我目前正在尝试将包含我从相机返回的 jpeg 图像的流保存到本地存储文件夹.正在创建文件，但不幸的是根本不包含任何数据.这是我尝试使用的代码:

I'm currently trying to save an stream containing a jpeg image I got back from the camera to the local storage folder. The files are being created but unfortunately contain no data at all. Here is the code I'm trying to use:

public async Task SaveToLocalFolderAsync(Stream file, string fileName)
{
  StorageFolder localFolder = ApplicationData.Current.LocalFolder;
  StorageFile storageFile = await localFolder.CreateFileAsync(fileName, CreationCollisionOption.ReplaceExisting);

  using (IRandomAccessStream fileStream = await storageFile.OpenAsync(FileAccessMode.ReadWrite))
  {
    using (IOutputStream outputStream = fileStream.GetOutputStreamAt(0))
    {
      using (DataWriter dataWriter = new DataWriter(outputStream))
      {
        dataWriter.WriteBytes(UsefulOperations.StreamToBytes(file));
        await dataWriter.StoreAsync();
        dataWriter.DetachStream();
      }
      await outputStream.FlushAsync();
    }
  }
}

public static class UsefulOperations
{
  public static byte[] StreamToBytes(Stream input)
  {
    using (MemoryStream ms = new MemoryStream())
    {
      input.CopyTo(ms);
      return ms.ToArray();
    }
  } 
}

以这种方式保存文件的任何帮助将不胜感激 - 我在网上找到的所有帮助都是指保存文本.我正在使用 Windows.Storage 命名空间，因此它也应该适用于 Windows 8.

Any help saving files this way would be greatly appreciated - all help I have found online refer to saving text. I'm using the Windows.Storage namespace so it should work with Windows 8 too.

推荐答案

您的方法 SaveToLocalFolderAsync 运行良好.我在我传入的 Stream 上试用了它，它按预期复制了其完整内容.

Your method SaveToLocalFolderAsync is working just fine. I tried it out on a Stream I passed in and it copied its complete contents as expected.

我猜这是您传递给该方法的流状态的问题.也许你只需要事先用 file.Seek(0, SeekOrigin.Begin); 将它的位置设置到开头.如果这不起作用，请将该代码添加到您的问题中，以便我们为您提供帮助.

I guess it's a problem with the state of the stream that you are passing to the method. Maybe you just need to set its position to the beginning beforehand with file.Seek(0, SeekOrigin.Begin);. If that doesn't work, add that code to your question so we can help you.

此外，您可以使代码更简单.如果没有中间类，以下内容完全相同:

Also, you could make your code much simpler. The following does exactly the same without the intermediate classes:

public async Task SaveToLocalFolderAsync(Stream file, string fileName)
{
    StorageFolder localFolder = ApplicationData.Current.LocalFolder;
    StorageFile storageFile = await localFolder.CreateFileAsync(fileName, CreationCollisionOption.ReplaceExisting);
    using (Stream outputStream = await storageFile.OpenStreamForWriteAsync())
    {
        await file.CopyToAsync(outputStream);
    }
}

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