c# - Turn event into a async call

Question

I'm wrapping a library for my own use. To get a certain property I need to wait for an event. I'm trying to wrap that into an async call.

Basically, I want to turn

void Prepare()
{
    foo = new Foo();
    foo.Initialized += OnFooInit;
    foo.Start();
}
string Bar
{
    return foo.Bar;  // Only available after OnFooInit has been called.
}

Into this

async string GetBarAsync()
{
    foo = new Foo();
    foo.Initialized += OnFooInit;
    foo.Start();
    // Wait for OnFooInit to be called and run, but don't know how
    return foo.Bar;
}

How could this best be accomplished? I could just loop and wait, but I'm trying to find a better way such as using Monitor.Pulse(), AutoResetEvent or something else.

Answer 1

Thats where TaskCompletionSource comes into play. There is little room for the new async keyword here. Example:

Task<string> GetBarAsync()
{
    TaskCompletionSource<string> resultCompletionSource = new TaskCompletionSource<string>();

    foo = new Foo();
    foo.Initialized += OnFooInit;
    foo.Initialized += delegate
    {
        resultCompletionSource.SetResult(foo.Bar);
    };
    foo.Start();

    return resultCompletionSource.Task;
}

Sample use (with fancy async)

async void PrintBar()
{
    // we can use await here since bar returns a Task of string
    string bar = await GetBarAsync();

    Console.WriteLine(bar);
}