Cannot await on async method

Question

I am creating a Xamarin application with a shared core. In the shared core I have a connection class for socket communication:

public class ConstantConnection {
    public async Task Connect()
    {
        await conn.Connect (); // Calls a socket plugin to connect
        timer = new Timer (new Action<object> (ParseData), "", 100, 1, false); // starts a local timer
    }

    public async Task Disconnect()
    {
        timer.Dispose ();   // End timer
        await conn.Disconnect (); // Close socket
    }
}

Now I have another class, working like a constructor, that would like to use objects of the above class by executing:

conn = new ConstantConnection();
await conn.Connect();

This gives me an error in Xamarin Studio which says:

The 'await' operator can only be used within an async method

As far I as I can see Connect is async . Why can't I use await ?

Answer 1

The error says it all. The method which has the awaiting code should also be async.

public async void ConnectAsync()
{
    conn = new ConstantConnection ();
    await conn.Connect ();
}

Answer 2

As others have pointed out, await can only be used within an async method. However, you should not use async void !

Since your calling code is a constructor, you'll have to rethink your approach. I describe a variety of approaches on my blog , of which I prefer the async factory method:

private MyConstructor()
{
  conn = new ConstantConnection();
}

public async Task<MyConstructor> CreateAsync()
{
  var result = new MyConstructor();
  await result.Connect();
}

As a side note, your task-returning methods should be named with an Async suffix to follow the TAP guidelines . Eg, Connect should be ConnectAsync , etc.

Answer 3

Awaiting an async method can only be done in an async method. So you have to create a async method, and then await Connect() :

public async void SomeAsync()
{
    await conn.Connect();
}

Else, if you want to run that code in a synchronous method (one not having the async keyword), you should call Wait in order to wait until that method has finished:

conn.Connect().Wait();

Answer 4

I agree with Stephen, async void is called "Fire and Forget", it's can bring a lot of issues to your code.

Always use:

public async Task<"Type"> Example()
{ 
}

or in "void" case use:

 public async Task Example()
 {
 }

All MVP's recomend this...