调用从非异步方法异步方法 [英] Calling an async method from a non-async method

问题描述

在以下code，我尽量不工作每一个变化 - 无论是 DoSomething的（）：无效，被称为书面，或 DoSomething的（）：任务，被称为与 TaskEx.RunEx（），一些尝试涉及 .GetAwaiter（） .GetResult（）。看到错误包括：开始可能不会被称为与空操作的任务，RunSynchronously可能无法绑定到委托的任务被称为和的任务尚未完成。

Every variation on the following code that I try doesn't work - whether DoSomething() : void and is called as written, or DoSomething() : Task and is called with TaskEx.RunEx(), some attempt involving .GetAwaiter().GetResult(). Errors seen include: "Start may not be called on a task with null action", "RunSynchronously may not be called on a task unbound to a delegate", and "The task has not yet completed".

class Program
{
    static void Main(string[] args) // Starting from a non-async method
    {
        DoSomething();

        Console.WriteLine("Press any key to quit.");
        Console.ReadKey();
    }

    static async void DoSomething()
    {
        Console.WriteLine("Starting DoSomething ...");

        var x = await PrepareAwaitable(1);

        Console.WriteLine("::" + x);

        var y = await PrepareAwaitable(2);

        Console.WriteLine("::" + y);
    }

    static Task<string> PrepareAwaitable(int id)
    {
        return new Task<string>(() =>
        {
            return "Howdy " + id.ToString();
        });
    }
}

输出：

开始DoSomething的...

Starting DoSomething ...

preSS任意键退出。

Press any key to quit.

prepareAwaitable 的任务的动作稍后将变得更复杂。当这个动作完成，但久，需要，我希望在工作（或其他框架机制），通过分配恢复你好...... 为x，再后来到y。我真正想要做的是拦截期待已久的对象，处理它们，在我控制一段时间以后，重新开始与结果的延续（ X 和是）。但我还没有已经越来越上大步很远，所以我想开始变小。

PrepareAwaitable's Task's Action will be more complicated later. When this action completes, however long that takes, I would expect the Task (or other Framework mechanisms) to resume by assigning "Howdy ..." to x, and then later to y. What I REALLY want to do is intercept the awaited objects, process them, and at some later time that I control, resume to the continuation with a result (x and y). But I haven't been getting very far on that big step, so I'm trying to start smaller.

推荐答案

您回来还没有开始的任务（即，他们是冷的任务）;尝试用以下替换prepareAwaitable code：

The tasks you returned haven't started yet (i.e., they're "cold" tasks); try replacing the PrepareAwaitable code with the following:

static Task<string> PrepareAwaitable(int x)
{
    return Task.Factory.StartNew<string>(() =>
    {
        return "Howdy " + x.ToString();
    });
}

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