Xamarin.Android : start an activity and wait for the result

Question

I need to start an activity to ask the user to grant the app battery saving exemption. The user must respond yes to be able to continue:

Here is the -buggy- code I have so far:

   PowerManager pm = (PowerManager)Android.App.Application.Context.GetSystemService(Context.PowerService);
        while (!pm.IsIgnoringBatteryOptimizations(this.ApplicationContext.PackageName))
        {
            IPopupService popupService = Locator.GetSharedInstance<IPopupService>();
            await popupService.DisplayAlertAsync(
                BusinessResources.GoToPowerSettingsTitle,
                BusinessResources.GoToPowerSettingsMessage,
                BusinessResources.Ok).ConfigureAwait(true);
            using (var intent = new Intent(Android.Provider.Settings.ActionRequestIgnoreBatteryOptimizations, Android.Net.Uri.Parse("package:" + Forms.Context.PackageName)))
            {
                Forms.Context.StartActivity(intent);
            }
        }

Because StartActivity won't wait, I'll ask the user once more than needed.

Now I've searched for a possible solution and found ActivityTask and ActivityController.

I am confused right now. Which one should I use, provided that Xamarin Forms is on the way?

Answer 1

All right, I solved my problem by awaiting an AsyncAutoResetEvent after launching the activity:

An event is defined as well as a handshake value:

   private AsyncAutoResetEvent dozeStandby;
   private int dozeStandbyHandshake = nameof(dozeStandbyHandshake).GetHashCode(StringComparison.InvariantCultureIgnoreCase);

During the activity creation, I'm prompting the user to allow the settings. Because I'm using StartActivityForResult, OnActivityResult will be called when the prompt activity finishes:

    protected override async void OnCreate(Bundle bundle)
    {
        dozeStandby = new AsyncAutoResetEvent();

        PowerManager pm = (PowerManager)Android.App.Application.Context.GetSystemService(Context.PowerService);
        while (!pm.IsIgnoringBatteryOptimizations(this.ApplicationContext.PackageName))
        {
              IPopupService popupService = Locator.GetSharedInstance<IPopupService>();
              await popupService.DisplayAlertAsync(
                        BusinessResources.GoToPowerSettingsTitle,
                        BusinessResources.GoToPowerSettingsMessage,
                        BusinessResources.Ok).ConfigureAwait(true);
              using (var intent = new Intent(Android.Provider.Settings.ActionRequestIgnoreBatteryOptimizations, Android.Net.Uri.Parse("package:" + Android.App.Application.Context.PackageName)))
              {
                  this.StartActivityForResult(intent, dozeStandbyHandshake);
                  await this.dozeStandby.WaitAsync().ConfigureAwait(true);
              }
         }
    }

In here I check the handshake to set the event.

    protected override void OnActivityResult(int requestCode, Result resultCode, Intent data)
    {
        if (requestCode == dozeStandbyHandshake)
        {
            this.dozeStandby.Set();
        }
    }