变换的IEnumerable＆LT;任务＆LT; T＆GT;＆GT;异步地等待每个任务 [英] Transform IEnumerable<Task<T>> asynchronously by awaiting each task

问题描述

今天，我想知道如何等待每次它变换的任务列表。
请看下面的例子：

Today I was wondering how to transform a list of Tasks by awaiting each of it. Consider the following example:

private static void Main(string[] args)
{
    try
    {
        Run(args);                
        Console.ReadLine();
    }
    catch (Exception ex)
    {
        Console.WriteLine(ex.ToString());
        Console.ReadLine();
    }
}

static async Task Run(string[] args)
{
    //Version 1: does compile, but ugly and List<T> overhead
    var tasks1 = GetTasks();                       

    List<string> gainStrings1 = new List<string>();
    foreach (Task<string> task in tasks1)
    {
        gainStrings1.Add(await task);
    }
    Console.WriteLine(string.Join("", gainStrings1));

    //Version 2: does not compile
    var tasks2 = GetTasks();
    IEnumerable<string> gainStrings2 = tasks2.Select(async t => await t);
    Console.WriteLine(string.Join("", gainStrings2));
}

static IEnumerable<Task<string>> GetTasks()
{
    string[] messages = new[] { "Hello", " ", "async", " ", "World" };

    for (int i = 0; i < messages.Length; i++)
    {
        TaskCompletionSource<string> tcs = new TaskCompletionSource<string>();
        tcs.SetResult(messages[i]);
        yield return tcs.Task;
    }
}

我想改变我的任务列表，而不在foreach，但无论是匿名函数的语法，也不是通常的函数语法允许我做我的foreach做什么。

I'd like to transform my list of Tasks without the foreach, however either the anonymous function syntax nor the usual function syntax allows me to do what my foreach does.

我必须依靠我的foreach和列表＆LT; T＆GT; 或有没有什么办法让它与的IEnumerable＆LT工作; T＆GT ; 及其所有优点

Do I have to rely on my foreach and the List<T> or is there any way to get it to work with IEnumerable<T> and all its advantages?

推荐答案

这个是什么：

await Task.WhenAll(tasks1);
var gainStrings = tasks1.Select(t => t.Result).ToList();

等待所有任务的结束，然后提取结果。这是理想的，如果你不介意的次序，他们就完成了。

Wait for all tasks to end and then extract results. This is ideal if you don't care in which order they are finished.

EDIT2：
更好的方法：

Even better way:

var gainStrings = await Task.WhenAll(tasks1);

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