TaskCompletionSource in async function

Question

I have such a function:

public async Task<bool> DoSomething()
{
   var tcs = new TaskCompletionSource<bool>();

   // Here is the problem. I need to keep this line because I wait on something asynchronously, but the function must return bool and I can't just return tcs.Task
   while(something)
      await Task.Delay(100);

   someobject.somevent += () => {
      // do some sht
      tcs.SetResult(true);
   }

   // it doesn't work
   return tcs.Task;
}

It's just a fake code but I have real situation where I need this. I want to keep DoSomething asynchronous but I also want to keep Task.Delay/Sleep in it. How do I do this in not-async function returning just Task?

UPDATE:

THIS WORKS:

class Program
    {
        static TaskCompletionSource<bool> tcs = new TaskCompletionSource<bool>();


        static Task<bool> Test()
        {
           // tcs = new TaskCompletionSource<bool>();
            Task.Factory.StartNew(() =>
            {
                Console.WriteLine("Waiting...");
                Thread.Sleep(5000);
                Console.WriteLine("Setting result");
                if(tcs.TrySetResult(true))
                    Console.WriteLine("Result has been set");


            });

            return tcs.Task;
        }

        static async Task Test2()
        {
            Console.WriteLine("Starting awaiting");
            var result = await Test();
            Console.WriteLine(result.ToString());
        }

        static void Main(string[] args)
        {


            Test2();

            Console.ReadKey(false);

        }
    }

and this doesn't

static async Task<bool> Test()
{
   // tcs = new TaskCompletionSource<bool>();
    Task.Factory.StartNew(() =>
    {
        Console.WriteLine("Waiting...");
        Thread.Sleep(5000);
        Console.WriteLine("Setting result");
        if(tcs.TrySetResult(true))
            Console.WriteLine("Result has been set");


    });


    return await tcs.Task;
}

what's worse, I have tested it in my windows forms app and awaiting tcs.Task caused weird crash coming from System.Threading....dll

Answer 1

If I understand correctly (it's tricky because your question isn't that easy to follow) you can restate things as follows:

public async Task<bool> DoSomething()
{
   var tcs = new TaskCompletionSource<bool>();
   someobject.somevent += () => {
      // do some sht
      tcs.SetResult(true);
   }

   return await tcs.Task;
}

Answer 2

The whole thing will come out a lot more elegantly if you separate out the logic of turning the event firing into a Task into its own method.

public static Task<bool> WhenSomeEvent(this SomeObject someobject)
{
    var tcs = new TaskCompletionSource<bool>();
    Action handler = null;
    handler = () =>
    {
        tcs.SetResult(true);
        someobject.SomeEvent -= handler;
    };
    someobject.SomeEvent += handler;
    return tcs.Task;
}

This allows you to write the business logic separately, without mixing in all of the logic of translating the event into a Task:

public async Task<bool> DoSomething()
{
    while(something)
        await Task.Delay(100);

    return await someobject.WhenSomeEvent();
}