How do I get a return value from Task.WaitAll() in a console app?

问题

I am using a console app as a proof of concept and new need to get an async return value.

I figured out that I need to use Task.WaitAll() in my main method to avoid needing an async "main()" method, which is illegal.

I'm now stuck trying to figure out an overload that allows me to use generics or just returns an object that I can cast, but while in Main().

回答1:

You don't get a return value from Task.WaitAll. You only use it to wait for completion of multiple tasks and then get the return value from the tasks themselves.

var task1 = GetAsync(1);
var task2 = GetAsync(2);
Task.WaitAll(task1, task2);
var result1 = task1.Result;
var result2 = task2.Result;

If you only have a single Task, just use the Result property. It will return your value and block the calling thread if the task hasn't finished yet:

var task = GetAsync(3);
var result = task.Result;

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It's generally not a good idea to synchronously wait (block) on an asynchronous task ("sync over async"), but I guess that's fine for a POC.

回答2:

For best practice, use the new async way of doing things. Instead of

• Task.WaitAll use await Task.WhenAll
• Task.WaitAny use await Task.WhenAny

The code above can be written as:

var task1 = GetAsync(1);
var task2 = GetAsync(2);
var results = await Task.WhenAll(task1, task2);
var result1 = results[0];
var result2 = results[1];

来源：https://stackoverflow.com/questions/25319484/how-do-i-get-a-return-value-from-task-waitall-in-a-console-app