Using transaction when dropping tables, so that the DB never enters

an inconsistant state

Bug: 34720697
Change-Id: I55a26d63be6c06622da6ee3395bf1990f1a58a11

src/com/android/launcher3/LauncherModel.java

@@ -815,7 +815,7 @@ public class LauncherModel extends BroadcastReceiver
             if (clearDb) {
                 Log.d(TAG, "loadWorkspace: resetting launcher database");
                 LauncherSettings.Settings.call(contentResolver,
-                        LauncherSettings.Settings.METHOD_DELETE_DB);
+                        LauncherSettings.Settings.METHOD_CREATE_EMPTY_DB);
             }
 
             Log.d(TAG, "loadWorkspace: loading default favorites");

src/com/android/launcher3/LauncherProvider.java

@@ -406,18 +406,13 @@ public class LauncherProvider extends ContentProvider {
                 return result;
             }
             case LauncherSettings.Settings.METHOD_CREATE_EMPTY_DB: {
-                createEmptyDB();
+                mOpenHelper.createEmptyDB(mOpenHelper.getWritableDatabase());
                 return null;
             }
             case LauncherSettings.Settings.METHOD_LOAD_DEFAULT_FAVORITES: {
                 loadDefaultFavoritesIfNecessary();
                 return null;
             }
-            case LauncherSettings.Settings.METHOD_DELETE_DB: {
-                // Are you sure? (y/n)
-                mOpenHelper.createEmptyDB(mOpenHelper.getWritableDatabase());
-                return null;
-            }
         }
         return null;
     }
@@ -469,13 +464,6 @@ public class LauncherProvider extends ContentProvider {
         values.put(LauncherSettings.ChangeLogColumns.MODIFIED, System.currentTimeMillis());
     }
 
-    /**
-     * Clears all the data for a fresh start.
-     */
-    synchronized private void createEmptyDB() {
-        mOpenHelper.createEmptyDB(mOpenHelper.getWritableDatabase());
-    }
-
     private void clearFlagEmptyDbCreated() {
         Utilities.getPrefs(getContext()).edit().remove(EMPTY_DATABASE_CREATED).commit();
     }
@@ -518,12 +506,12 @@ public class LauncherProvider extends ContentProvider {
 
             // There might be some partially restored DB items, due to buggy restore logic in
             // previous versions of launcher.
-            createEmptyDB();
+            mOpenHelper.createEmptyDB(mOpenHelper.getWritableDatabase());
             // Populate favorites table with initial favorites
             if ((mOpenHelper.loadFavorites(mOpenHelper.getWritableDatabase(), loader) <= 0)
                     && usingExternallyProvidedLayout) {
                 // Unable to load external layout. Cleanup and load the internal layout.
-                createEmptyDB();
+                mOpenHelper.createEmptyDB(mOpenHelper.getWritableDatabase());
                 mOpenHelper.loadFavorites(mOpenHelper.getWritableDatabase(),
                         getDefaultLayoutParser(widgetHost));
             }
@@ -825,9 +813,15 @@ public class LauncherProvider extends ContentProvider {
          * Clears all the data for a fresh start.
          */
         public void createEmptyDB(SQLiteDatabase db) {
-            db.execSQL("DROP TABLE IF EXISTS " + Favorites.TABLE_NAME);
-            db.execSQL("DROP TABLE IF EXISTS " + WorkspaceScreens.TABLE_NAME);
-            onCreate(db);
+            db.beginTransaction();
+            try {
+                db.execSQL("DROP TABLE IF EXISTS " + Favorites.TABLE_NAME);
+                db.execSQL("DROP TABLE IF EXISTS " + WorkspaceScreens.TABLE_NAME);
+                onCreate(db);
+                db.setTransactionSuccessful();
+            } finally {
+                db.endTransaction();
+            }
         }
 
         /**

src/com/android/launcher3/LauncherSettings.java

@@ -291,7 +291,6 @@ public class LauncherSettings {
         public static final String METHOD_NEW_SCREEN_ID = "generate_new_screen_id";
 
         public static final String METHOD_CREATE_EMPTY_DB = "create_empty_db";
-        public static final String METHOD_DELETE_DB = "delete_db";
 
         public static final String METHOD_LOAD_DEFAULT_FAVORITES = "load_default_favorites";