入口点不能被打上了“异步”修饰符

本文介绍了入口点不能被打上了“异步”修饰符的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！ 问题描述

我复制下面code从this link.But当我编译这个code我得到一个切入点不能打上异步修改即可。我怎样才能让这个code编译？

类节目{    异步静态无效的主要（字串[] args）    {        任务＆LT;串GT; getWebPageTask = GetWebPageAsync（msdn.microsoft）;        的Debug.WriteLine（在startButton_Click的await之前）;        字符串webText =等待getWebPageTask;        的Debug.WriteLine（字符收到：+ webText.Length.ToString（））;    }    私有静态异步任务＆LT;串GT; GetWebPageAsync（字符串URL）    {        //开始一个异步任务。        任务＆LT;串GT; getStringTask =（新的HttpClient（））GetStringAsync（URL）。        //等待任务。这是发生了什么：        // 1.执行立即返回到调用方法，返回        //从previous语句创建的任务不同的任务。        //这个方法执行暂停。        // 2.在previous语句完成，创建任务        //从GetStringAsync方法结果由等待产生        //声明，并继续执行该方法中。        的Debug.WriteLine（在GetWebPageAsync的await之前）;        字符串webText =等待getStringTask;        的Debug.WriteLine（以GetWebPageAsync后AWAIT）;        返回webText;    }    //输出：    //在GetWebPageAsync之前的await    //在startButton_Click之前的await    //在GetWebPageAsync后的await    //人物好评：44306}

解决方案

该错误信息是完全正确的：的Main（）方法不能是异步，因为当的Main（）的回报，应用程序通常结束。

如果你想使用一个控制台应用程序异步，一个简单的解决方案是创建一个异步版本的的Main（）并同步等待（）上，从实际的Main（）：

静态无效的主要（）{    MainAsync（）等待（）。}静态异步任务MainAsync（）{    //你的异步code在这里}

这就是混合的罕见的情况下有一个等待和等待（）是一个好主意，你不应该T通常做到这一点。

更新：异步主要是的目前预期，使之成为C＃7.0 。

I copied below code from this link.But when I am compiling this code I am getting an entry point cannot be marked with the 'async' modifier. How can I make this code compilable?

class Program { static async void Main(string[] args) { Task<string> getWebPageTask = GetWebPageAsync("msdn.microsoft"); Debug.WriteLine("In startButton_Click before await"); string webText = await getWebPageTask; Debug.WriteLine("Characters received: " + webText.Length.ToString()); } private static async Task<string> GetWebPageAsync(string url) { // Start an async task. Task<string> getStringTask = (new HttpClient()).GetStringAsync(url); // Await the task. This is what happens: // 1. Execution immediately returns to the calling method, returning a // different task from the task created in the previous statement. // Execution in this method is suspended. // 2. When the task created in the previous statement completes, the // result from the GetStringAsync method is produced by the Await // statement, and execution continues within this method. Debug.WriteLine("In GetWebPageAsync before await"); string webText = await getStringTask; Debug.WriteLine("In GetWebPageAsync after await"); return webText; } // Output: // In GetWebPageAsync before await // In startButton_Click before await // In GetWebPageAsync after await // Characters received: 44306 }

解决方案

The error message is exactly right: the Main() method cannot be async, because when Main() returns, the application usually ends.

If you want to make a console application that uses async, a simple solution is to create an async version of Main() and synchronously Wait() on that from the real Main():

static void Main() { MainAsync().Wait(); } static async Task MainAsync() { // your async code here }

This is one of the rare cases where mixing await and Wait() is a good idea, you shouldn't usually do that.

Update: Async Main is currently expected to make it into C# 7.0.