2014-10-09 199 views
0

我想有一个方法,它将一个System.IO.Stream作为输入并使用它将数据写入文件。到目前为止,我有以下几点:如何将数据从流保存到WinRT中的文件?

public async Task SaveStreamToFileX(Stream stream, string filePath, IProgress<long> progress) 
    { 

     var folder = await StorageFolder.GetFolderFromPathAsync(Path.GetDirectoryName(filePath)); 

     var fileName = Path.GetFileName(filePath); 
     StorageFile file = await folder.CreateFileAsync(fileName, CreationCollisionOption.OpenIfExists); 

     var istream = stream.AsInputStream(); 

     var canRead = stream.CanRead; //this returns true 

     using (var reader = new DataReader(istream)) 
     { 
      using (IRandomAccessStream fileStream = await file.OpenAsync(FileAccessMode.ReadWrite)) 
      { 
       using (IOutputStream outputStream = fileStream.GetOutputStreamAt(0)) 
       { 
        using (DataWriter writer = new DataWriter(outputStream)) 
        { 
         IBuffer buffer; 
         long readBytes = 0; 
         const int bufferSize = 8192; 
         while ((buffer = reader.ReadBuffer(bufferSize)).Length > 0) //exception System.Exception with message: Out of range ... 
         { 
          writer.WriteBuffer(buffer); 
          readBytes += bufferSize; 
          progress.Report(readBytes); 
         } 
        } 
       } 
      } 
     } 

    } 

问题是,当我尝试读while循环(先读)数据的异常(超出范围)被抛出。流应该有数据。我不确定是否这么长的代码是坏的,如果有人有更好的解决方案,它会很好。 附注: 如果我尝试await reader.LoadAsync(50)它返回50.我不确定LoadAsync应该做什么。也许我必须在阅读之前调用它以准备读取数据?我将进一步调查... 此外,Stream.CanRead返回true。

回答

1

问题不在于转换流,正如我原先的想法。这只是缺乏知识如何在WinRT中完成文件的工作(我认为微软的文档非常糟糕)。

与我collegue与尝试多种方式的帮助下结束,并与下面的结束:

public async Task SaveStreamToFile(Stream stream, string filePath, IProgress<long> progress) 
    { 
     var folder = await StorageFolder.GetFolderFromPathAsync(Path.GetDirectoryName(filePath)); 

     var fileName = Path.GetFileName(filePath); 
     StorageFile file = await folder.CreateFileAsync(fileName, CreationCollisionOption.OpenIfExists); 

     var istream = stream.AsInputStream(); 

     using (var reader = new DataReader(istream)) 
     { 
      using (IRandomAccessStream fileStream = await file.OpenAsync(FileAccessMode.ReadWrite)) 
      { 
       using (IOutputStream outputStream = fileStream.GetOutputStreamAt(0)) 
       { 
        using (DataWriter writer = new DataWriter(outputStream)) 
        { 
         long writtenBytes = 0; 
         const int bufferSize = 8192; 

         uint loadedBytes = 0; 
         while ((loadedBytes = (await reader.LoadAsync(bufferSize))) > 0) //!!! 
         { 
          IBuffer buffer = reader.ReadBuffer(loadedBytes); 
          writer.WriteBuffer(buffer); 
          uint tmpWritten = await writer.StoreAsync(); //!!! 
          writtenBytes += tmpWritten; 
          progress.Report(writtenBytes); 
         } 
        } 
       } 
      } 
     } 
    }  

我希望看到一些更简单的实现,但这个工程。问题是缺少LoadAsync(这似乎是调用所必需的),并且在写入操作期间必须调用StoreAsync以提交数据(刷新不足)。

我希望这可以帮助别人。

0

我会建议不要那种代码,而应该利用Windows Runtime Interop extension methods。这将产生更整洁和更可读的代码,例如:

private async Task CopyToTempFile(Stream stream, string temporaryFileName) { 

    var file = await ApplicationData.Current.TemporaryFolder.CreateFileAsync(temporaryFileName, CreationCollisionOption.ReplaceExisting); 

    using (var outputstream = await file.OpenStreamForWriteAsync()) { 
     await stream.CopyToAsync(outputstream); 
    } 
} 
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