using System;

using System.Threading;

using System.Threading.Tasks;

public class Controller {

    private Random _random = new Random(Guid.NewGuid().GetHashCode());

    private TimeSpan _workDelay = TimeSpan.FromSeconds(1);

    public int DoWork() {

        // pretend todo heavy work

        Thread.Sleep(_workDelay);

        return _random.Next();

    }

    public async Task<int> DoWorkAsync() {

        // pretend todo heavy work

        await Task.Delay(_workDelay);

        return _random.Next();

    }

    public async Task<int> DoWorkAsync(IProgress<double> progress) {

        progress.Report(0);

        const int COUNT = 5;

        TimeSpan delay = TimeSpan.FromTicks(_workDelay.Ticks / COUNT);

        // pretend todo heavy work in splitted parts

        for (int i = 0; i < COUNT; ++i)

        {

            await Task.Delay(delay);

            progress.Report(1.0 * (i + 1) / COUNT);

        }

        return _random.Next();

    }

}

​

public class Program

{

    private static bool s_buttonEnabled;

    private static string s_labelValue;

    private static Controller s_controller = new Controller();

    public static async Task Main()

    {       

        OnClick_1();

        await PretendUserWaitingAsync();

        OnClick_2();

        await PretendUserWaitingAsync();

        OnClick_3();

        await PretendUserWaitingAsync();

    }

    private static void OnClick_1()

    {

        s_buttonEnabled = false;

        // we offload the sync work on to a thread pool thread to allow the GUI to work

        var _ = Task.Run((Action)HandleClick_1);

    }

    private static void OnClick_2()

    {

        s_buttonEnabled = false;

        // we really want to offload the async task on to a thread pool thread

        var _ = Task.Run((Func<Task>)HandleClick_2Async);

    }

    private static void OnClick_3() 

    {

        s_buttonEnabled = false;

        // we really want to offload the async task on to a thread pool thread

        var _ = Task.Run((Func<Task>)HandleClick_3Async);

    }

    private static void SetResult(int result)

    {

        Console.WriteLine("Result: {0}", result);

    }

    private static void SetProgress(double progress)

    {

        Console.WriteLine("Progress: {0:P2}", progress);    

    }

    private static async Task PretendUserWaitingAsync()

    {       

        while (!s_buttonEnabled) {

            await Task.Delay(250);  

        }

    }

    private static void HandleClick_1()

    {

        try

        {

            var result = s_controller.DoWork();

            SetResult(result);

        }

        finally

        {

            s_buttonEnabled = true; 

        }

    }

    private static async Task HandleClick_2Async()

    {

        try

        {

            var result = await s_controller.DoWorkAsync();

            SetResult(result);

        }

        finally

        {

            s_buttonEnabled = true; 

        }

    }

    private static async Task HandleClick_3Async()

    {

        try

        {

            var progress = new Progress<double>(SetProgress);

            var result = await s_controller.DoWorkAsync(progress);

            SetResult(result);

        }

        finally

        {

            s_buttonEnabled = true; 

        }

    }

}