Turn a sync method into an async one

async-await, c#

Solution

To answer your 2nd part first, yes you need to mark the event for the button `async`, if you want to use the keyword `await` in your code you must declare the function `async`.

2ndly if a function uses `async` without having an `await` inside of it the code will not be run asynchronously, you either need to create a task and run your synchronous method inside of it or rewrite the method to be asynchronous.

As task method:

private async void button1_Click(object sender, EventArgs e)
{
    txtLog.AppendText("Before Await");

    //Note I changed from "Task<bool>" to "bool", await is like calling ".Result" 
    //  on a task but not blocking the UI, so you store the type you are waiting for.
    bool result = await Task.Run(() => login("","")); //You would still use your old login code before you tried to make it async, it requires no modifications.

    txtLog.AppendText("After Await");
    txtLog.AppendText("Result: " + result.ToString());
}

Rewriting the function method:

private async void button1_Click(object sender, EventArgs e)
{
    txtLog.AppendText("Before Await");

    //Note I changed from "Task<bool>" to "bool", await is like calling ".Result" 
    //  on a task but not blocking the UI, so you store the type you are waiting for.
    bool result = await login("",""); 

    txtLog.AppendText("After Await");
    txtLog.AppendText("Result: " + result.ToString());
}

private Task<bool> login(String username, String password)
{
    var tcs = new TaskCompletionSource<bool>();

    // Make the login request
    var request = new RestSharp.RestRequest("/accounts/login/", RestSharp.Method.POST);
    request.AddParameter("username", username);
    request.AddParameter("password", password);

    client.ExecuteAsync(request, (response, handle) =>
        {
            try
            {
                // Return loggin status
                var dom = response.Content;

                //dom["html"] did not have a .HasClass in my tests, so this code may need work.
                tcs.TrySetResult(dom["html"].HasClass("logged-in")); 
            }
            catch(Exception ex)
            {
                tcs.TrySetException(ex);
            }
        });

    return tcs.Task;
}

In my "rewrite method" what I am doing is I am using `ExecuteAsync` witch is part of IRestClient. That function calls a callback method when it completes, in the callback method I call `tcs`'s `SetResult` to report back the result I wanted.

You could expand this further by taking in a `CancellationToken` and if the token is raised call `Abort()` on `RestRequestAsyncHandle`, however if we do this we need to bring the `async` back in to the function and await the result so we can clean up after the cancellation token registration.

private Task<bool> login(String username, String password)
{
    return login(username, password, CancellationToken.None);
}

private async Task<bool> login(String username, String password, CancellationToken cancelToken)
{
    var tcs = new TaskCompletionSource<bool>();

    // Make the login request
    var request = new RestSharp.RestRequest("/accounts/login/", RestSharp.Method.POST);
    request.AddParameter("username", username);
    request.AddParameter("password", password);

    var asyncHandle = client.ExecuteAsync(request, (response, handle) =>
        {
            try
            {
                // Return loggin status
                var dom = response.Content;

                tcs.TrySetResult(dom["html"].HasClass("logged-in")); 
            }
            catch(Exception ex)
            {
                tcs.TrySetException(ex);
            }
        });

    //if the token is canceled it will call `asyncHandle.Abort()` for us.
    using(cancelToken.Register(() =>
        {
           if(tcs.TrySetCanceled(cancelToken))
               asyncHandle.Abort();
        }))
    {
        return await tcs.Task;
    }
}

Problem

Original source