实时连接 - 异步和等待阻止UI

Question

Now I think I understand why this happening so I guess my question is how can I modify the code to act how I want.

First the code.

private void btnLiveSignin_Click(object sender, RoutedEventArgs e)
{
    var LoggedIn = Login();

    busy.Visibility = System.Windows.Visibility.Visible;  // Display the please wait message

    if (LoggedIn.Result)
    {
        // Do something 
    }
}

public async Task<bool> Login()
{
    try
    {
        var e = await lac.InitializeAsync(Scopes);

        if (e.Status == LiveConnectSessionStatus.Connected)
        {
            client = new LiveConnectClient(e.Session);

            // do some stuff now that we are connected

            return true;
        }
        else
        {
            // not connected so do something

            return false;
        }
    }
    catch (Exception ex)
    {
        return false;
    }
}

Basically when the user clicks a button it will log them in to their windows live account and while that is happening a message appears asking the user to please wait.

As you can guess the UI locks so the message never appears. How can I change it so the UI doesn't lock?

I done this with windows phone 7.5 before using events as the sdk didn't use async, and that worked perfectly fine. Would this require a mixture of asyncing and events?

Answer 1

What you're missing from your handler is async and await .

Because you marked your Login method as async and made it return a task, you've made it awaitable , which makes it possible to re-write your event-handler as:

private async void btnLiveSignin_Click(object sender, RoutedEventArgs e)
{
    var loginTask = this.Login();

    busy.Visibility = System.Windows.Visibility.Visible; 

    await loginTask;

    if(loginTask.Result)
    {
       // Do something 
    }
}

Marking the event-handler as async indicates to the caller that it will complete asynchronously. What await does is "signal" that you want to wait for the task to complete before continuing. Together this means that the event-handler can return an "incomplete" result back to the dispatcher (the UI thread) which will run in the background without disrupting the UI.

As a rule, once you start using async and await in your code, you should try using them "all the way down".

async and await are a bit devious in how the compiler turns them into "real" code, so don't be surprised if you need to read more around the topic to understand them fully.

Answer 2

You need to await the task rather than doing a blocking wait (which is want Result does).

private async void btnLiveSignin_Click(object sender, RoutedEventArgs e)
{
    busy.Visibility = System.Windows.Visibility.Visible;  // Display the please wait message

    if(await Login())
    {
       // Do something 
    }
}