Add configurable back button behavior

src/main/java/com/todoroo/astrid/activity/TaskEditFragment.java

@@ -39,6 +39,7 @@ import org.tasks.fragments.TaskEditControlSetFragmentManager;
 import org.tasks.injection.ForActivity;
 import org.tasks.injection.InjectingFragment;
 import org.tasks.notifications.NotificationManager;
+import org.tasks.preferences.Preferences;
 import org.tasks.ui.MenuColorizer;
 import org.tasks.ui.TaskEditControlFragment;
 
@@ -78,6 +79,7 @@ public final class TaskEditFragment extends InjectingFragment implements Toolbar
     @Inject @ForActivity Context context;
     @Inject TaskEditControlSetFragmentManager taskEditControlSetFragmentManager;
     @Inject CommentsController commentsController;
+    @Inject Preferences preferences;
 
     @Bind(R.id.toolbar) Toolbar toolbar;
     @Bind(R.id.comments) LinearLayout comments;
@@ -109,13 +111,19 @@ public final class TaskEditFragment extends InjectingFragment implements Toolbar
             isNewTask = savedInstanceState.getBoolean(EXTRA_IS_NEW_TASK);
         }
 
-        Drawable drawable = DrawableCompat.wrap(getResources().getDrawable(R.drawable.ic_save_24dp));
+        final boolean backButtonSavesTask = preferences.backButtonSavesTask();
+        Drawable drawable = DrawableCompat.wrap(getResources().getDrawable(
+                backButtonSavesTask ? R.drawable.ic_close_24dp : R.drawable.ic_save_24dp));
         DrawableCompat.setTint(drawable, getResources().getColor(android.R.color.white));
         toolbar.setNavigationIcon(drawable);
         toolbar.setNavigationOnClickListener(new View.OnClickListener() {
             @Override
             public void onClick(View v) {
-                save();
+                if (backButtonSavesTask) {
+                    discardButtonClick();
+                } else {
+                    save();
+                }
             }
         });
         toolbar.inflateMenu(R.menu.task_edit_fragment);

src/main/java/com/todoroo/astrid/activity/TaskListActivity.java

@@ -302,7 +302,11 @@ public class TaskListActivity extends InjectingAppCompatActivity implements
 
         TaskEditFragment taskEditFragment = getTaskEditFragment();
         if (taskEditFragment != null) {
-            taskEditFragment.discardButtonClick();
+            if (preferences.backButtonSavesTask()) {
+                taskEditFragment.save();
+            } else {
+                taskEditFragment.discardButtonClick();
+            }
         } else if (!isFinishing()) {
             super.onBackPressed();
         }

src/main/java/org/tasks/preferences/Preferences.java

@@ -50,6 +50,10 @@ public class Preferences {
         publicPrefs = context.getSharedPreferences(AstridApiConstants.PUBLIC_PREFS, Context.MODE_WORLD_READABLE);
     }
 
+    public boolean backButtonSavesTask() {
+        return getBoolean(R.string.p_back_button_saves_task, false);
+    }
+
     public boolean quietHoursEnabled() {
         return getBoolean(R.string.p_rmd_enable_quiet, false);
     }

src/main/res/values/keys.xml

@@ -278,5 +278,6 @@
   <string name="default_vibration_duration">1000</string>
   <string name="default_vibration_pause">500</string>
   <string name="p_collect_statistics">collect_statistics</string>
+  <string name="p_back_button_saves_task">back_button_saves_task</string>
 
 </resources>

src/main/res/values/strings.xml

@@ -893,6 +893,7 @@ File %1$s contained %2$s.\n\n
     <string name="doze_notifications_off">Android will significantly delay notifications while device is in Doze mode</string>
     <string name="doze_notifications_on">Android will allow limited interruptions while device is in Doze mode</string>
   <string name="no_title">(No title)</string>
+  <string name="back_button_saves_task">Back button saves task</string>
 
   <string-array name="sync_SPr_interval_entries">
         <!-- sync_SPr_interval_entries: Synchronization Intervals -->

src/main/res/xml/preferences_appearance.xml

@@ -27,6 +27,11 @@
             android:key="@string/customize_edit_screen"
             android:title="@string/customize_edit_screen"/>
 
+        <com.todoroo.astrid.ui.MultilineCheckboxPreference
+            android:defaultValue="false"
+            android:key="@string/p_back_button_saves_task"
+            android:title="@string/back_button_saves_task" />
+
         <com.todoroo.astrid.ui.MultilineCheckboxPreference
             android:defaultValue="true"
             android:key="@string/p_show_task_edit_comments"