Improve performance of detail page by cancelling useless async tasks

android/uhabits-core/src/main/java/org/isoron/uhabits/core/tasks/CancelableTask.java

@@ -0,0 +1,37 @@
+/*
+ * Copyright (C) 2016 Álinson Santos Xavier <isoron@gmail.com>
+ *
+ * This file is part of Loop Habit Tracker.
+ *
+ * Loop Habit Tracker is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by the
+ * Free Software Foundation, either version 3 of the License, or (at your
+ * option) any later version.
+ *
+ * Loop Habit Tracker is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
+ * or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
+ * more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+package org.isoron.uhabits.core.tasks;
+
+public abstract class CancelableTask implements Task
+{
+    private boolean isCanceled = false;
+
+    @Override
+    public synchronized void cancel()
+    {
+        isCanceled = true;
+    }
+
+    @Override
+    public synchronized boolean isCanceled()
+    {
+        return isCanceled;
+    }
+}

android/uhabits-core/src/main/java/org/isoron/uhabits/core/tasks/SingleThreadTaskRunner.java

@@ -35,10 +35,13 @@ public class SingleThreadTaskRunner implements TaskRunner
     public void execute(Task task)
     {
         for(Listener l : listeners) l.onTaskStarted(task);
-        task.onAttached(this);
-        task.onPreExecute();
-        task.doInBackground();
-        task.onPostExecute();
+        if(!task.isCanceled())
+        {
+            task.onAttached(this);
+            task.onPreExecute();
+            task.doInBackground();
+            task.onPostExecute();
+        }
         for(Listener l : listeners) l.onTaskFinished(task);
     }
 

android/uhabits-core/src/main/java/org/isoron/uhabits/core/tasks/Task.java

@@ -25,6 +25,11 @@ public interface Task
 {
     default void cancel() {}
 
+    default boolean isCanceled()
+    {
+        return false;
+    }
+
     void doInBackground();
 
     default void onAttached(@NonNull TaskRunner runner) {}