using System;

using System.Threading.Tasks;

public class Program

{

    public static async Task Main()

    {

        var cam = new AsyncCamera(new Camera());

        Console.WriteLine("Capture");

        _ = await cam.CaptureAsync();

        Console.WriteLine("Back");

        Console.WriteLine("SubscriberCount: {0}", cam.GetSubscriberCount());

    }

}

​

public class ReadResult{}

public class ControllerProxy{}

​

public class Camera 

{

     public void RequestCapture(){

         System.Threading.Thread.Sleep(1000);

         var handler = OnReadResult;

         handler?.Invoke(null, new ReadResult());

     }

     public delegate void ReadResultEventHandler(ControllerProxy sender, ReadResult readResult);

     public event ReadResultEventHandler OnReadResult;

     public int GetSubscriberCount()

     {

         var invocList = OnReadResult?.GetInvocationList();

         return (invocList is null) ? 0 : invocList.Length;

     }

}

​

public class AsyncCamera

{

    private readonly Camera camera;

    public AsyncCamera(Camera camera)

    {

        this.camera = camera ?? throw new ArgumentNullException(nameof(camera));

    } 

​

    public Task<ReadResult> CaptureAsync()

    {

         Camera.ReadResultEventHandler handler = null;

         TaskCompletionSource<ReadResult> tcs = new TaskCompletionSource<ReadResult>();

​

         handler = (sender, result) => {

             camera.OnReadResult -= handler;

             tcs.TrySetResult(result);

         };

​

         camera.OnReadResult += handler;

         camera.RequestCapture();

         return tcs.Task;

    }

    public int GetSubscriberCount()

    {

        return camera.GetSubscriberCount();

    }

}