Question

我有以下代码，

    private void button1_Click(object sender, RoutedEventArgs e)
    {
        button1.IsEnabled = false;

        var s = File.ReadAllLines("Words.txt").ToList(); // my WPF app hangs here
        // do something with s

        button1.IsEnabled = true;
    }

Words.txt有很多单词我读入s变量，我试图使用async在C＃5中使用await和Async CTP Library个关键字WPF应用程序不会挂起。到目前为止，我有以下代码，

    private async void button1_Click(object sender, RoutedEventArgs e)
    {
        button1.IsEnabled = false;

        Task<string[]> ws = Task.Factory.FromAsync<string[]>(
            // What do i have here? there are so many overloads
            ); // is this the right way to do?

        var s = await File.ReadAllLines("Words.txt").ToList();  // what more do i do here apart from having the await keyword?
        // do something with s

        button1.IsEnabled = true;
    }

目标是以异步方式读取文件而不是同步，以避免冻结WPF应用程序。

感谢任何帮助，谢谢！

Answer 1

使用Task.Run，它本质上是Task.Factory.StartNew的包装器，用于异步包装器is a code smell。

如果您不想通过阻塞功能浪费CPU线程，则应等待真正的异步IO方法StreamReader.ReadToEndAsync，如下所示：

using (var reader = File.OpenText("Words.txt"))
{
    var fileText = await reader.ReadToEndAsync();
    // Do something with fileText...
}

这会将整个文件作为string而不是List<string>。如果您需要换行，您可以在之后轻松拆分字符串，如下所示：

using (var reader = File.OpenText("Words.txt"))
{
    var fileText = await reader.ReadToEndAsync();
    return fileText.Split(new[] { Environment.NewLine }, StringSplitOptions.None);
}

编辑：以下是一些与File.ReadAllLines实现相同代码的方法，但是采用真正的异步方式。代码基于File.ReadAllLines本身的实现：

using System.Collections.Generic;
using System.IO;
using System.Text;
using System.Threading.Tasks;

public static class FileEx
{
    /// <summary>
    /// This is the same default buffer size as
    /// <see cref="StreamReader"/> and <see cref="FileStream"/>.
    /// </summary>
    private const int DefaultBufferSize = 4096;

    /// <summary>
    /// Indicates that
    /// 1. The file is to be used for asynchronous reading.
    /// 2. The file is to be accessed sequentially from beginning to end.
    /// </summary>
    private const FileOptions DefaultOptions = FileOptions.Asynchronous | FileOptions.SequentialScan;

    public static Task<string[]> ReadAllLinesAsync(string path)
    {
        return ReadAllLinesAsync(path, Encoding.UTF8);
    }

    public static async Task<string[]> ReadAllLinesAsync(string path, Encoding encoding)
    {
        var lines = new List<string>();

        // Open the FileStream with the same FileMode, FileAccess
        // and FileShare as a call to File.OpenText would've done.
        using (var stream = new FileStream(path, FileMode.Open, FileAccess.Read, FileShare.Read, DefaultBufferSize, DefaultOptions))
        using (var reader = new StreamReader(stream, encoding))
        {
            string line;
            while ((line = await reader.ReadLineAsync()) != null)
            {
                lines.Add(line);
            }
        }

        return lines.ToArray();
    }
}

Answer 2

使用Stream.ReadAsync异步读取文件

private async void Button_Click(object sender, RoutedEventArgs e)
{
    string filename = @"c:\Temp\userinputlog.txt";
    byte[] result;

    using (FileStream SourceStream = File.Open(filename, FileMode.Open))
    {
        result = new byte[SourceStream.Length];
        await SourceStream.ReadAsync(result, 0, (int)SourceStream.Length);
    }

    UserInput.Text = System.Text.Encoding.ASCII.GetString(result);
}

Read MSDN Stream.ReadAsync

Answer 3

如果要异步读取文件中的所有行，则可以使用async功能来使用FileStream访问文件。

private static async Task<string[]> ReadAllLinesAsync(string filePath)
    {
        using (FileStream sourceStream = new FileStream(filePath,
            FileMode.Open, FileAccess.Read, FileShare.Read,
            bufferSize: 4096, useAsync: true))
        {
            StringBuilder sb = new StringBuilder();

            byte[] buffer = new byte[0x1000];
            int numRead;
            while ((numRead = await sourceStream.ReadAsync(buffer, 0, buffer.Length)) != 0)
            {
                string text = Encoding.Unicode.GetString(buffer, 0, numRead);
                sb.Append(text);
            }

            return sb.ToString().Split(new[] { Environment.NewLine },StringSplitOptions.None);
        }
    }

您可以通过在事件处理函数中指定async来在事件处理函数中使用async方法。

这是您可以使用的方式，这不会让您的GUI线程冻结。

private async void button1_Click(object sender, RoutedEventArgs e)
{
    button1.IsEnabled = false;

    var s = await ReadAllLinesAsync("Words.txt").ToList();
    // do something with s

    button1.IsEnabled = true;
}

有关更多详细信息，请参见MS Docs

Answer 4

我也遇到了问题中描述的问题。我在以前的答案中解决了它的简单性：

driver
  .elementByAccessibilityId('FOO')

Answer 5

试试这个：

private async void button1_Click(object sender, RoutedEventArgs e)
{
    button1.IsEnabled = false;
    try
    {
        var s = await Task.Run(() => File.ReadAllLines("Words.txt").ToList());
        // do something with s
    }
    finally
    {
        button1.IsEnabled = true;
    }
}

修改

你不需要try-finally就可以了。这真的只是你需要改变的一条线。解释它是如何工作的：这会生成另一个线程（实际上从线程池中获取一个）并获取该线程来读取该文件。当文件读完后，将调用button1_Click方法的其余部分（来自GUI线程）并显示结果。请注意，这可能不是最有效的解决方案，但它可能是对代码的最简单更改，它不会阻止GUI。

如何异步Files.ReadAllLines并等待结果？

5 个答案: