在Windows 8中写入文件时异步

本文关键字：文件 异步 Windows | 更新日期: 2023-09-27 17:49:33

当我执行按钮单击事件并在打开时写入文本文件时，它仍然挂起UI线程的任何原因。在写完之前我什么都做不了。

private async void WriteFileClick(object sender, RoutedEventArgs e)
    {
        string fileName = @"asyn3cfile.txt";
        string text = "Hello async, this was written while you were doing something else in the UI";
        StorageFolder storageFolder = KnownFolders.DocumentsLibrary;
        var writtenFile = await storageFolder.CreateFileAsync(fileName, CreationCollisionOption.ReplaceExisting);
        using (IRandomAccessStream randomAccessStream = await writtenFile.OpenAsync(FileAccessMode.ReadWrite))
        {
            Stream stream = randomAccessStream.AsStreamForWrite();
            stream.Seek(0, SeekOrigin.Begin);
            WriteFileTextAsync(text, stream);
            await stream.FlushAsync();
            await randomAccessStream.FlushAsync();
        }
        Debug.WriteLine("{0} was created", fileName);
    }
    private async static void WriteFileTextAsync(string text, Stream stream)
    {
        for (int i = 0; i < 100; i++)
        {
            var fileText = string.Format("{0} in process {1}'n", text, i);
            byte[] textBytes = Encoding.UTF8.GetBytes(fileText);
            stream.SetLength(stream.Length + textBytes.Length);
            await stream.WriteAsync(textBytes, 0, textBytes.Length);
            new System.Threading.ManualResetEvent(false).WaitOne(100);
        }
    }

XAML 

<Button x:Name="WriteFileInDocumentsButton" Content="Write a text file" Click="WriteFileClick"/>

的原因吗?

在Windows 8中写入文件时异步

你应该改变:

 private async static void WriteFileTextAsync(string text, Stream stream)
{
    for (int i = 0; i < 100; i++)
    {
        var fileText = string.Format("{0} in process {1}'n", text, i);
        byte[] textBytes = Encoding.UTF8.GetBytes(fileText);
        stream.SetLength(stream.Length + textBytes.Length);
        await stream.WriteAsync(textBytes, 0, textBytes.Length);
        new System.Threading.ManualResetEvent(false).WaitOne(100);
    }
}


 private async static Task GetFileTextAsync(string text, Stream stream)
{
    StringBuilder sb = new StringBuilder();
    for (int i = 0; i < 100; i++)
    {
        sb.AppendLine(string.Format("{0} in process {1}'n", text, i));            
    }
    await stream.WriteAsync(textBytes, 0, textBytes.Length);
}

这将有助于节省一些开销，但更重要的是，您必须更改:

 using (IRandomAccessStream randomAccessStream = await writtenFile.OpenAsync(FileAccessMode.ReadWrite))
    {
        Stream stream = randomAccessStream.AsStreamForWrite();
        stream.Seek(0, SeekOrigin.Begin);
        WriteFileTextAsync(text, stream);
        await stream.FlushAsync();
        await randomAccessStream.FlushAsync();
    }
    Debug.WriteLine("{0} was created", fileName);

在WriteFileAysnc方法调用中包含await关键字。

using (IRandomAccessStream randomAccessStream = await writtenFile.OpenAsync(FileAccessMode.ReadWrite))
    {
        Stream stream = randomAccessStream.AsStreamForWrite();
        stream.Seek(0, SeekOrigin.Begin);
        **await** WriteFileTextAsync(text, stream);
        await stream.FlushAsync();
        await randomAccessStream.FlushAsync();
    }
    Debug.WriteLine("{0} was created", fileName);

您编写的代码中存在一些错误。你没有在等待WriteAsync, WriteFileTextAsync应该返回一个任务，并等待。

如果你只是写字符串，你会发现使用FileIO辅助方法更容易。

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