App is not loading the Views a second time if receiving a message from MessagingCenter and updating the UI afterwards

Question

I am sending an intent I am receiving through a BroadcastReceiver to multiple Views in my shared-project. The DisplayResult-method implements the MessagingCenter.Send.

public class MyBroadcast : BroadcastReceiver
{
        public override void OnReceive(Context context, Intent intent)
        {
            String action = intent.Action;
            if (action.Equals(MainActivity.Instance.Resources.GetString(intentString)))
            {
                
                //Device.BeginInvokeOnMainThread(() => MainActivity.Instance.DisplayResult(intent)); 
                //Task.Run(() => MainActivity.Instance.DisplayResult(intent));
                //MainActivity.Instance.RunOnUiThread(() => MainActivity.Instance.DisplayResult(intent));
            }
        }
}

If a message is received I want to update my Views e.g. like this:

MessagingCenter.Subscribe<object, Model>(this, "HI", (sender, arg) =>
                {   
                    
                        var dt = DateTime.Now;
                        _logger.Debug($"Task started: {dt}");
                        
                        ActivityIndicator.IsVisible = true;
                        ActivityIndicator.IsRunning = true;
                        
                        Task.Run(async () =>
                        {                            
                            await SomeTask();                          
                        }).GetAwaiter().GetResult();
                        _logger.Debug($"Task finished: {DateTime.Now - dt}");
                        
                        ActivityIndicator.IsRunning = false;
                        ActivityIndicator.IsVisible = false;
                        
                    }
                });

The issue is if I use the approach with Task.Run(...) my Views are only showing up once but the ActivityIndicator is running. That means if I close a View and go back to the MainPage and navigate to another or the same View again it only shows a white screen.

If I use either Device.BeginInvokeOnMainThread(...) or RunOnUiThread(...) I get the skipped frames error. And my app is frozen until every Task within the MessagingCenter.Subscribe in my Views is finished. The ActivityIndicator is Not showing up.

score 1 · Accepted Answer · answered Aug 18 '20 at 02:41

You can have a try with using async method to invoke these method as follow:

MessagingCenter.Subscribe<PageMain, string>(this, "HI", async (sender, arg) =>
{
    var dt = DateTime.Now;
    _logger.Debug($"Task started: {dt}");

    ActivityIndicator.IsVisible = true;
    ActivityIndicator.IsRunning = true;

    await SomeTask();

    _logger.Debug($"Task finished: {DateTime.Now - dt}");

    ActivityIndicator.IsVisible = false;
    ActivityIndicator.IsRunning = false;
});

App is not loading the Views a second time if receiving a message from MessagingCenter and updating the UI afterwards

1 Answers1