Xamarin.Forms更新UI线程在iOS和Android中表现奇怪

Question

I am using async, await to update UI on button click to indicate user that some progress is going on and I am showing loading panel onclick of button. Below is my code:

Android:

async void loginButtonGesture_Tapped(object sender, EventArgs e)
{            
    try
    {
    DependencyService.Get<Idevice>().StartLoading();
        await AsyncUpdateStatus();
    }
}


private async Task AsyncUpdateStatus()
{
            try
            {
                await Task.Run(() =>
                {
                      //Device.BeginInvokeOnMainThread is used in places to stop loading the screen
                });
           }
}

iOS:

async void loginButtonGesture_Tapped(object sender, EventArgs e)
    {            
        try
        {
        DependencyService.Get<Idevice>().StartLoading();
            await Task.Delay(40); //Required for iOS, otherwise loading panel is keep on running
            await AsyncUpdateStatus();
        }
    }


    private async Task AsyncUpdateStatus()
    {
                try
                {

                     //await Task.Run(() => Enabling new thread also not working
                    //Device.BeginInvokeOnMainThread is used in places to stop loading the screen

               }
    }

Both Android & iOS is sharing same Forms code. But for this particular case its working conditionally. iOS is working after adding Task.Delay(40) and commenting Task.Run(() => {}); thread.

Why its so? But if I do above modification in Android, it is not working. What exactly is happening?

Answer 1

Somehow you are blocking the UIThread, there are numerous questions on Xamarin Forums about this:

https://forums.xamarin.com/discussion/47019/activity-indicator-inconsistencies

https://forums.xamarin.com/discussion/54237/update-uitextview-text-in-code

https://forums.xamarin.com/discussion/41229/best-practise-waiting-and-synchronising-threads

And it seems that you are doing this in your View class, you should do this inside your ViewModel, By experience I encourage you to don't wait a Task unless is completely necessary otherwise you should use Bindings to let the user that something is going on!

Most of them answered by Adam