我想有一个方法,它将System.IO.Stream作为输入,并使用它将数据从它写入文件。到目前为止,我有以下内容:
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,当我尝试在循环(第一次读取)中读取数据时,抛出异常(超出范围)。流应该有数据。我不确定是否有这么长的代码是必要的,如果有人有更好的解决方案它会很棒。
边注:
如果我尝试await reader.LoadAsync(50)
它会返回50.我不确定LoadAsync应该做什么。也许我必须在读取之前调用它来为读取准备数据?我会进一步研究这个......
此外,Stream.CanRead返回true。
答案 0 :(得分:1)
问题不在于转换流,正如我想象的那样。缺少知识如何在WinRT中完成文件的工作(在我看来,微软的文档非常糟糕)。
最后在我的同事的帮助下尝试了几种方法并最终得到以下结论:
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,但这有效。问题是缺少LoadAsync
(这似乎是调用所必需的),并且在写操作期间必须调用StoreAsync
才能提交数据(刷新是不够的)。
我希望这有助于某人。
答案 1 :(得分:1)
我会反对这种代码,而是利用Windows Runtime Interop extension methods。这将产生更整洁,更易读的代码,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);
}
}