在Visual Studio中调用异步HttpClient.GetAsync()后调试器停止 [英] Debugger stops after async HttpClient.GetAsync() call in visual studio

问题描述

我正在尝试测试以下http请求方法

I'm trying to test the follwing http request method

public async Task<HttpContent> Get(string url)
    {
        using (HttpClient client = new HttpClient())
// breakpoint
        using (HttpResponseMessage response = await client.GetAsync(url))
// can't reach anything below this point
        using (HttpContent content = response.Content)
        {
            return content;
        }
    }

但是，调试器似乎正在跳过第二条注释下方的代码.我正在使用Visual Studio 2015 RC，有什么想法吗?我还尝试检查任务"窗口，什么也没看到

However, the debugger seems to be skipping the code below the 2nd comment. I'm using Visual studio 2015 RC, any ideas? I also tried checking the Tasks window and saw nothing

找到了解决方法

using System;
using System.Net.Http;
using System.Threading.Tasks;

namespace ConsoleTests
{
    class Program
    {
        static void Main(string[] args)
        {
            Program program = new Program();
            var content = program.Get(@"http://www.google.com");
            Console.WriteLine("Program finished");
        }

        public async Task<HttpContent> Get(string url)
        {
            using (HttpClient client = new HttpClient())
            using (HttpResponseMessage response = await client.GetAsync(url).ConfigureAwait(false))
            using (HttpContent content = response.Content)
            {
                return content;
            }
        }
    }
}

结果证明，因为这是一个C#控制台应用程序，所以我猜它在主线程结束后就结束了，因为在添加Console.ReadLine()并稍等片刻之后，请求确实返回了.我猜想C#会等到我的任务执行后才结束，但是我想我错了.如果有人能详细说明发生这种情况的原因，那将是很好的.

Turns out that because this was a C# console app it ended after the main thread ends I guess, because after adding a Console.ReadLine() and waiting a bit, the request did return. I guessed that C# would wait until my task execute and not end before it, but I suppose I was wrong. If anybody could elaborate on why this happened it would be nice.

推荐答案

Main退出时，程序退出.任何未完成的异步操作都将被取消，其结果将被丢弃.

When Main exits, the program exits. Any outstanding asynchronous operations are canceled and their results discarded.

因此，您需要通过阻止异步操作或其他方法来阻止Main退出(例如，调用Console.ReadKey进行阻止，直到用户按下按键为止):

So, you need to block Main from exiting, either by blocking on the asynchronous operation or some other method (e.g., calling Console.ReadKey to block until the user hits a key):

static void Main(string[] args)
{
  Program program = new Program();
  var content = program.Get(@"http://www.google.com").Wait();
  Console.WriteLine("Program finished");
}

一种常见的方法是定义一个同时执行异常处理的MainAsync:

One common approach is to define a MainAsync that does exception handling as well:

static void Main(string[] args)
{
  MainAsync().Wait();
}

static async Task MainAsync()
{
  try
  {
    Program program = new Program();
    var content = await program.Get(@"http://www.google.com");
    Console.WriteLine("Program finished");
  }
  catch (Exception ex)
  {
    Console.WriteLine(ex);
  }
}

注意，阻塞异步代码通常被认为是一个坏主意；在极少数情况下应该执行此操作，而控制台应用程序的Main方法恰好是其中之一.

Note that blocking on asynchronous code is generally considered a bad idea; there are very few cases where it should be done, and a console application's Main method just happens to be one of them.

这篇关于在Visual Studio中调用异步HttpClient.GetAsync()后调试器停止的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！