Xamarin forms. The app crashes in the background.

Question

Hi everybody. I have a problem with my program, it uses Essentials: Accelerometer to count the number of device tilts.But the problem is that sometimes it doesn't work, and sometimes it works, but not stably, when the phone is in the background or when the screen is locked.The program also uses Essentials: Vibration, which also does not work or is unstable in the background or in a locked screen mode.I also tried to use the services to work in the background, but they did not bring results, or maybe I implemented them incorrectly??? Please help me find a solution for this situation, that's also my github // https://github.com/Ilim-Hussein/MyMobilProject // I put together a test code sample there having such a problem. Thanks !

Answer 1

Hello,​

I test your demo, I find you create DoLongRunningOperationThings method in DataSource.cs, but this method is empty. Please move your Accelerometer.ReadingChanged += Accelerometer_ReadingChanged; code to DoLongRunningOperationThings method and move related code from AboutPage.cs to DataSource.cs.

When I click the start button, make the application in background and lock the screen. When I get counter meet the If condition, I get the Vibtate normally. My test device is
android 9.0 and android 1.0.

===========
Update=============

If you want to transfer data from DataSource.cs to MainPage.xaml.cs

For example, I transfer result data from Accelerometer_ReadingChanged method of DataSource.cs like following code.

   void Accelerometer_ReadingChanged(object sender, AccelerometerChangedEventArgs e)  
            {  
                var data = e.Reading;  
                result = counter / 2;  
   //add transfer code here  
               MessagingCenter.Send<Object, string>(this, "TestMessage", result.ToString());  
           }  

Then, you can get result in MainPage.xaml.cs , for testing, I set the text for Rakaat_1.Text

   public MainPage()  
           {  
               InitializeComponent();  
     
               MessagingCenter.Subscribe<Object, string>(this, "TestMessage", (sender, arg) =>  
               {  
                   string message = arg;  
                   Rakaat_1.Text = message;  
               });  
                
           }  

Best Regards,

Leon Lu

---

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Answer 2

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using Xamarin.Forms;
using Xamarin.Essentials;
namespace AlgoritmForegraundPR
{
    public partial class MainPage : ContentPage
    {
        public MainPage()
        {
            InitializeComponent();
        }

        //Here, at the click of the button, we must accept the message and the message variable must be initialized to our Rakaat_1.Text
        public void Click_Start(object sender, System.EventArgs e) //Start button
        {
            DependencyService.Get<IAndroidService>().StartService();
            DependencyService.Get<IAccelerometrST>().StartAccelerometer();
           // Checking the activation of the Accelerometer.
            if (Accelerometer.IsMonitoring) { Rakaat_1.Text = "1"; }
        }


        public void Click_Stop (object sender, System.EventArgs e) //Stop button
        {
            DependencyService.Get<IAndroidService>().StopService();
            DependencyService.Get<IAccelerometrST>().StopAccelerometer();
           // Check turning off the Accelerometer.
            if (Accelerometer.IsMonitoring == false) { Rakaat_1.Text = "Start counter";}
        }


    }
}





using Android.App;
using Android.Content;
using Android.OS;
using Android.Runtime;
using Android.Views;
using Android.Widget;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using Xamarin.Forms;
using Xamarin.Essentials;
using System.Threading.Tasks;


[assembly: Xamarin.Forms.Dependency(typeof(AlgoritmForegraundPR.Droid.DataSource))]

namespace AlgoritmForegraundPR.Droid
{
    [Service]
    public class DataSource : Service , IAccelerometrST
    {
        MainPage aboutPage = new MainPage();
        public override IBinder OnBind(Intent intent)
        {
            return null;
        }
        public const int ServiceRunningNotifID = 9000;


        public override StartCommandResult OnStartCommand(Intent intent, StartCommandFlags flags, int startId)
        {
            Notification notif = DependencyService.Get<INotification>().ReturnNotif();
            StartForeground(ServiceRunningNotifID, notif);

            _ = DoLongRunningOperationThings();

            return StartCommandResult.Sticky;
        }
        public object DoLongRunningOperationThings()
        {
            Accelerometer.ReadingChanged += Accelerometer_ReadingChanged;

            return null;
        }


        public override void OnDestroy()
        {
            base.OnDestroy();
        }

        public override bool StopService(Intent name)
        {
            return base.StopService(name);
        }




        public float num1 = 0.8f;
        public float num2 = 0.9f;
        public float num3 = 0.2f;
        public float num4 = 0.1f;

        public float Aceler_dataX = 0.0f;
        public float Aceler_dataY = 0.0f;
        public float Aceler_dataZ = 0.0f;

        public bool c;
        public bool d;

        public int counter;
        public int result;

        //The value of this variable must be sent to the MainPage class
        string message = "Hello";
        // Or The value of this variable must be sent to the MainPage class
        int message_num = 123;


        void Accelerometer_ReadingChanged(object sender, AccelerometerChangedEventArgs e)
         {
             var data = e.Reading;
             result = counter / 2;
             Aceler_dataX = data.Acceleration.X;
             Aceler_dataY = data.Acceleration.Y;
             Aceler_dataZ = data.Acceleration.Z;
             Result_Condition();

            aboutPage.Rakaat_1.Text = Convert.ToString(result);

             if (counter / 2 == 3)
             {
                 Vibtate_Controll(1);
             }

             else if (counter / 2 == 6)
             {
                 Vibtate_Controll(2);
             }

             else if (counter / 2 == 9)
             {
                 Vibtate_Controll(3);
             }

         }

        public bool ResultCounter_Y_1(bool condition) // checking the condition Y 1 - 0.8 to 0.9
        {
            if (Aceler_dataY >= num1 && Aceler_dataY <= num2)
            {
                condition = true;
            }
            else
            {
                condition = false;
            }
            return condition;
        }

        public bool ResultCounter_Y_2(bool condition) // checking the condition Y 2 - 0.2 to 0.1
        {
            if (Aceler_dataY <= num3 && Aceler_dataY >= num4)
            {
                condition = true;
            }
            else
            {
                condition = false;
            }
            return condition;
        }

        public void Result_Condition() //  Checking the fulfillment of conditions with Accelerometers and output counter +1 in the case of true true
        {

            if (ResultCounter_Y_1(false) == true) { c = true; }
            if (ResultCounter_Y_2(false) == true) { d = true; }

            if (c == true && d == true)
            {
                c = false;
                d = false;
                counter += 1;
            }
        }


        {
            Accelerometer.Start(SensorSpeed.UI);
            DependencyService.Get<IAndroidService>().StartService();
        }


        public void Click_Stop(object sender, System.EventArgs e) //Stop button
        {
            Accelerometer.Stop();
            DependencyService.Get<IAndroidService>().StopService();
            counter = 0;
            aboutPage.Rakaat_1.Text = "Start counter";
        }

        */

        public async void Vibtate_Controll(int count_vibr) //Vibration control
        {
            var durition = TimeSpan.FromSeconds(0.3);

            for (int i = 0; i < count_vibr; i++)
            {
                Vibration.Vibrate(durition);
                await Task.Delay(700);
            }
        }


        public void StartAccelerometer()
        {
            Accelerometer.Start(SensorSpeed.UI);
        }

        public void StopAccelerometer()
        {
            Accelerometer.Stop();
        }
    }
}