How to make an asynchronous method return a value?

Question

I know how to make asynchronous methods but say I have a method that does a lot of work and then returns a boolean value?

How should I return the boolean value on the callback?

Clarification:

public bool Foo()
{
    Thread.Sleep(100_000); // Do work.
    return true;
}

I want to be able to make this asynchronous.

Answer 1

There are a few ways of doing that... the simplest is to have the async method also do the follow-on operation. Another popular approach is to pass in a callback, i.e.

void RunFooAsync(..., Action<bool> callback) {
     // do some stuff
     bool result = ...

     if(callback != null) callback(result);
}

Another approach would be to raise an event (with the result in the event-args data) when the async operation is complete.

Also, if you are using the TPL, you can use ContinueWith:

Task<bool> outerTask = ...;
outerTask.ContinueWith(task =>
{
    bool result = task.Result;
    // do something with that
});