IntervalsFragment/IntervalStatisticsModel refactoring: better performance with AndroidViewModel (it doesn't recreate the model every track point done anymore).

Also, it doesn't jump anymore. Fixes #669.

src/main/java/de/dennisguse/opentracks/viewmodels/IntervalStatisticsModel.java

@@ -1,6 +1,11 @@
 package de.dennisguse.opentracks.viewmodels;
 
+import android.app.Application;
+
+import androidx.annotation.NonNull;
 import androidx.annotation.Nullable;
+import androidx.lifecycle.AndroidViewModel;
+import androidx.lifecycle.MutableLiveData;
 
 import java.util.ArrayList;
 import java.util.List;
@@ -12,33 +17,67 @@ import de.dennisguse.opentracks.util.UnitConversions;
  * This model is used to load intervals for a track.
  * It uses a default interval but it can be set from outside to manage the interval length.
  */
-public class IntervalStatisticsModel {
+public class IntervalStatisticsModel extends AndroidViewModel {
 
     private final List<TrackPoint> trackPoints = new ArrayList<>();
+    private MutableLiveData<List<IntervalStatistics.Interval>> intervalsLiveData;
+    private float distanceInterval;
 
-    public IntervalStatistics getIntervalStats(boolean metricUnits, @Nullable IntervalOption interval) {
+    public IntervalStatisticsModel(@NonNull Application application) {
+        super(application);
+    }
+
+    public MutableLiveData<List<IntervalStatistics.Interval>> getIntervalStats(boolean metricUnits, @Nullable IntervalOption interval) {
         synchronized (trackPoints) {
-            if (interval == null) {
-                interval = IntervalOption.OPTION_1;
-            }
+            if (intervalsLiveData == null) {
+                if (interval == null) {
+                    interval = IntervalOption.OPTION_1;
+                }
 
-            float distanceInterval = metricUnits ? (float) (interval.getValue() * UnitConversions.KM_TO_M) : (float) (interval.getValue() * UnitConversions.MI_TO_M);
-            return new IntervalStatistics(trackPoints, distanceInterval);
+                intervalsLiveData = new MutableLiveData<>();
+                distanceInterval = metricUnits ? (float) (interval.getValue() * UnitConversions.KM_TO_M) : (float) (interval.getValue() * UnitConversions.MI_TO_M);
+                loadIntervalStatistics();
+            }
+            return intervalsLiveData;
         }
     }
 
+    private void loadIntervalStatistics() {
+        IntervalStatistics intervalStatistics = new IntervalStatistics(trackPoints, distanceInterval);
+        intervalsLiveData.postValue(intervalStatistics.getIntervalList());
+    }
+
     public void add(TrackPoint trackPoint) {
         synchronized (trackPoints) {
             trackPoints.add(trackPoint);
         }
     }
 
+    public void onNewTrackPoints() {
+        synchronized (trackPoints) {
+            if (intervalsLiveData != null) {
+                loadIntervalStatistics();
+            }
+        }
+    }
+
     public void clear() {
         synchronized (trackPoints) {
             trackPoints.clear();
         }
     }
 
+    public void upload(boolean metricUnits, @Nullable IntervalOption interval) {
+        synchronized (trackPoints) {
+            if (interval == null) {
+                interval = IntervalOption.OPTION_1;
+            }
+
+            distanceInterval = metricUnits ? (float) (interval.getValue() * UnitConversions.KM_TO_M) : (float) (interval.getValue() * UnitConversions.MI_TO_M);
+            loadIntervalStatistics();
+        }
+    }
+
     /**
      * Intervals length this view model support.
      */