写一个异步方法，将等待布尔 [英] Write an Async method that will await a bool

问题描述

我想编写一个将await设置为true的方法.

I would like to write a method that will await for a variable to be set to true.

这是伪代码.

bool IsSomethingLoading = false
SomeData TheData;

public async Task<SomeData> GetTheData()
{
   await IsSomethingLoading == true;
   return TheData;
}

TheData将由棱镜事件以及IsSomethingLoading变量设置.

TheData will be set by a Prism Event along with the IsSomethingLoading variable.

我已经调用了GetTheData方法，但是我希望它运行异步(现在，如果数据还没有准备好，它只会返回null.(这会导致其他问题.)

I have a call to the GetTheData method, but I would like it to run async (right now it just returns null if the data is not ready. (That leads to other problems.)

有没有办法做到这一点?

Is there a way to do this?

推荐答案

在许多情况下，您需要的是TaskCompletionSource.

In many situations like this what you need is a TaskCompletionSource.

您可能拥有一种能够在某个时间点生成数据的方法，但是它不使用任务来执行该操作.也许有一种方法可以采用提供结果的回调，或者触发一个事件来表明存在结果，或者只是使用Thread或ThreadPool进行编码，而您不希望将其重构为使用Task.Run.

You likely have a method that is able to generate the data at some point in time, but it doesn't use a task to do it. Perhaps there is a method that takes a callback which provides the result, or an event that is fired to indicate that there is a result, or simply code using a Thread or ThreadPool that you are not inclined to re-factor into using Task.Run.

public Task<SomeData> GetTheData()
{
    TaskCompletionSource<SomeData> tcs = new TaskCompletionSource<SomeData>();
    SomeObject worker = new SomeObject();
    worker.WorkCompleted += result => tcs.SetResult(result);
    worker.DoWork();
    return tcs.Task;
}

虽然您可能需要/想要将TaskCompletionSource提供给工作人员或其他类，或者以其他方式将其提供给更广泛的范围，但我发现通常并不需要它，即使它非常适当时提供强大的选择.

While you may need/want to provide the TaskCompletionSource to the worker, or some other class, or in some other way expose it to a broader scope, I've found it's often not needed, even though it's a very powerful option when it's appropriate.

还可以使用Task.FromAsync基于异步操作创建任务，然后直接返回该任务，或者在代码中将其await退回.

It's also possible that you can use Task.FromAsync to create a task based on an asynchronous operation and then either return that task directly, or await it in your code.

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