如何使用 LINQ 异步等待任务列表? [英] How to await a list of tasks asynchronously using LINQ?

问题描述

我有一个像这样创建的任务列表:

I have a list of tasks that I created like this:

public async Task<IList<Foo>> GetFoosAndDoSomethingAsync()
{
    var foos = await GetFoosAsync();

    var tasks = foos.Select(async foo => await DoSomethingAsync(foo)).ToList();

    ...
}

通过使用.ToList()，任务应该都开始了.现在我想等待他们完成并返回结果.

By using .ToList(), the tasks should all start. Now I want to await their completion and return the results.

这适用于上面的 ... 块:

This works in the above ... block:

var list = new List<Foo>();
foreach (var task in tasks)
    list.Add(await task);
return list;

它做我想要的，但这看起来相当笨拙.我更愿意写一些像这样简单的东西:

It does what I want, but this seems rather clumsy. I'd much rather write something simpler like this:

return tasks.Select(async task => await task).ToList();

...但这不能编译.我错过了什么?还是只是不能这样表达?

... but this doesn't compile. What am I missing? Or is it just not possible to express things this way?

推荐答案

LINQ 不能与 async 代码完美配合，但您可以这样做:

LINQ doesn't work perfectly with async code, but you can do this:

var tasks = foos.Select(DoSomethingAsync).ToList();
await Task.WhenAll(tasks);

如果您的任务都返回相同类型的值，那么您甚至可以这样做:

If your tasks all return the same type of value, then you can even do this:

var results = await Task.WhenAll(tasks);

这很不错.WhenAll 返回一个数组，所以我相信你的方法可以直接返回结果:

which is quite nice. WhenAll returns an array, so I believe your method can return the results directly:

return await Task.WhenAll(tasks);

这篇关于如何使用 LINQ 异步等待任务列表?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！