Refactor BaseTask interface

app/src/androidTest/java/org/isoron/uhabits/unit/views/ViewTest.java

@@ -198,10 +198,9 @@ public class ViewTest extends BaseTest
         new BaseTask()
         {
             @Override
-            protected Void doInBackground(Void... params)
+            protected void doInBackground()
             {
                 view.refreshData();
-                return null;
             }
         }.execute();
 

app/src/main/java/org/isoron/uhabits/dialogs/HistoryEditorDialog.java

@@ -72,11 +72,9 @@ public class HistoryEditorDialog extends DialogFragment
         new BaseTask()
         {
             @Override
-            @SuppressWarnings("ResourceType")
-            protected Void doInBackground(Void... params)
+            protected void doInBackground()
             {
                 historyView.refreshData();
-                return null;
             }
         }.execute();
     }

app/src/main/java/org/isoron/uhabits/tasks/BaseTask.java

@@ -23,24 +23,27 @@ import android.os.AsyncTask;
 
 import java.util.concurrent.TimeoutException;
 
-public class BaseTask extends AsyncTask<Void, Void, Void>
+public abstract class BaseTask extends AsyncTask<Void, Void, Void>
 {
     private static int activeTaskCount;
 
     @Override
-    protected Void doInBackground(Void... params)
+    protected final Void doInBackground(Void... params)
     {
+        register();
+        doInBackground();
+        unregister();
         return null;
     }
 
-    @Override
-    protected void onPreExecute()
+    protected abstract void doInBackground();
+
+    protected void register()
     {
         activeTaskCount++;
     }
 
-    @Override
-    protected void onPostExecute(Void aVoid)
+    protected void unregister()
     {
         activeTaskCount--;
     }

app/src/main/java/org/isoron/uhabits/tasks/ExportCSVTask.java

@@ -19,7 +19,6 @@
 
 package org.isoron.uhabits.tasks;
 
-import android.os.AsyncTask;
 import android.support.annotation.Nullable;
 import android.view.View;
 import android.widget.ProgressBar;
@@ -80,12 +79,12 @@ public class ExportCSVTask extends BaseTask
     }
 
     @Override
-    protected Void doInBackground(Void... params)
+    protected void doInBackground()
     {
         try
         {
             File dir = DatabaseHelper.getFilesDir("CSV");
-            if(dir == null) return null;
+            if(dir == null) return;
 
             HabitsCSVExporter exporter = new HabitsCSVExporter(selectedHabits, dir);
             archiveFilename = exporter.writeArchive();
@@ -94,7 +93,5 @@ public class ExportCSVTask extends BaseTask
         {
             e.printStackTrace();
         }
-
-        return null;
     }
 }

app/src/main/java/org/isoron/uhabits/tasks/ExportDBTask.java

@@ -19,7 +19,6 @@
 
 package org.isoron.uhabits.tasks;
 
-import android.os.AsyncTask;
 import android.support.annotation.Nullable;
 import android.view.View;
 import android.widget.ProgressBar;
@@ -75,14 +74,14 @@ public class ExportDBTask extends BaseTask
     }
 
     @Override
-    protected Void doInBackground(Void... params)
+    protected void doInBackground()
     {
         filename = null;
 
         try
         {
             File dir = DatabaseHelper.getFilesDir("Backups");
-            if(dir == null) return null;
+            if(dir == null) return;
 
             filename = DatabaseHelper.saveDatabaseCopy(dir);
         }
@@ -90,7 +89,5 @@ public class ExportDBTask extends BaseTask
         {
             e.printStackTrace();
         }
-
-        return null;
     }
 }

app/src/main/java/org/isoron/uhabits/tasks/ImportDataTask.java

@@ -19,7 +19,6 @@
 
 package org.isoron.uhabits.tasks;
 
-import android.os.AsyncTask;
 import android.support.annotation.NonNull;
 import android.support.annotation.Nullable;
 import android.view.View;
@@ -86,7 +85,7 @@ public class ImportDataTask extends BaseTask
     }
 
     @Override
-    protected Void doInBackground(Void... params)
+    protected void doInBackground()
     {
         try
         {
@@ -106,7 +105,5 @@ public class ImportDataTask extends BaseTask
             result = FAILED;
             e.printStackTrace();
         }
-
-        return null;
     }
 }

app/src/main/java/org/isoron/uhabits/tasks/ToggleRepetitionTask.java

@@ -38,10 +38,9 @@ public class ToggleRepetitionTask extends BaseTask
     }
 
     @Override
-    protected Void doInBackground(Void... params)
+    protected void doInBackground()
     {
         habit.repetitions.toggle(timestamp);
-        return null;
     }
 
     @Override

app/src/main/java/org/isoron/uhabits/views/HabitHistoryView.java

@@ -388,13 +388,12 @@ public class HabitHistoryView extends ScrollableDataView implements HabitDataVie
     @Override
     public void onToggleRepetitionFinished()
     {
-        new BaseTask() {
+        new BaseTask()
+        {
             @Override
-            @SuppressWarnings("ResourceType")
-            protected Void doInBackground(Void... params)
+            protected void doInBackground()
             {
                 refreshData();
-                return null;
             }
 
             @Override

app/src/main/java/org/isoron/uhabits/widgets/BaseWidgetProvider.java

@@ -223,10 +223,9 @@ public abstract class BaseWidgetProvider extends AppWidgetProvider
         }
 
         @Override
-        protected Void doInBackground(Void... params)
+        protected void doInBackground()
         {
             refreshCustomViewData(widgetView);
-            return null;
         }
 
         @Override