成功调用 .build() 后未调用 RoomDatabase.Callback() 的 onCreate()

Question

我已经使用 Room Persisdent lib 创建了 MovieDatabase。根据 RoomDatabase.Callback 中 onCreate() 方法的文档，onCreate() 在第一次创建数据库后调用，所有表都创建完毕。

在我调用 buildPersistentDB() 之后发生的事情是，我收到了来自 MoviesDatabase 类的日志，该类用@Database 进行了注释，但是尽管我调用了 RoomDatabase.Callback 中来自 onCreate() 的日志，但从未调用过：

this.mMovieDatabase = this.mMovieDBPersistentBuilder.fallbackToDestructiveMigration().build();

我创建数据库的方式清楚地显示在 buildPersistentDB() 方法中。我还发布了 MovieDatabase 类，如下所示。

我想知道为什么我没有从 Room.Callback 中的 onCreate() 方法收到日志，尽管数据库已成功创建

代码_1：

public void buildPersistentDB() {
    Log.v(TAG_LOG, "->buildPersistentDB");
    this.mMovieDBPersistentBuilder = Room
            .databaseBuilder(getApplicationContext(), MovieDatabase.class, ActMain.DATA_BASE_NAME);

    this.mMovieDBPersistentBuilder.addCallback(new RoomDatabase.Callback() {
        @Override
        public void onCreate(@NonNull SupportSQLiteDatabase db) {
            super.onCreate(db);
            Log.v(TAG_LOG + "->onCreate", " buildPersistentDB->DB is created, all tables has been created");
            Log.d(TAG_LOG + "->onCreate", " buildPersistentDB->DB db.getPath(): " + db.getPath());
            Log.d(TAG_LOG + "->onCreate", " buildPersistentDB->DB db.toString(): " + db.toString());
            Log.d(TAG_LOG + "->onCreate", " buildPersistentDB->DB db.isOpen(): " + db.isOpen());
            Log.d(TAG_LOG + "->onCreate", " buildPersistentDB->DB db.isReadOnly(): " + db.isReadOnly());
        }

        @Override
        public void onOpen(@NonNull SupportSQLiteDatabase db) {
            super.onOpen(db);
            Log.v(TAG_LOG + "->onOpen", " buildPersistentDB->onCreate");
            Log.d(TAG_LOG + "->onOpen", " buildPersistentDB->DB has been opened");
        }
    });
    this.mMovieDatabase = this.mMovieDBPersistentBuilder.fallbackToDestructiveMigration().build();
     Log.d(TAG_LOG + "->buildPersistentDB", "->this.mMovieDatabase.isOpen(): " + this.mMovieDatabase.isOpen());
}//eof-buildPersistentDB

代码_2：

//class - The abstract class which is annotated with Database and extends RoomDatabase.
@Database(entities = {Movie.class}, version = 1, exportSchema = false)
public abstract class MovieDatabase extends RoomDatabase {
private final static String TAG_LOG = MovieDatabase.class.getSimpleName();

public abstract IDatabaseAccessObject dao();

public MovieDatabase() {
    super();
    Log.w(TAG_LOG, "->MovieDatabase constructor is called.");
}

@Override
public void init(@NonNull DatabaseConfiguration configuration) {
    super.init(configuration);
    Log.w(TAG_LOG, "->init is called.");
}

@NonNull
@Override
public SupportSQLiteOpenHelper getOpenHelper() {
    Log.w(TAG_LOG, "->init is called.");
    return super.getOpenHelper();
}

@NonNull
@Override
protected SupportSQLiteOpenHelper createOpenHelper(DatabaseConfiguration config) {
    Log.w(TAG_LOG, "->createOpenHelper is called.");
    Log.d(TAG_LOG, "->createOpenHelper->config.name:" + config.name);
    Log.d(TAG_LOG, "->createOpenHelper->config.callbacks:" + config.callbacks);
    Log.d(TAG_LOG, "->createOpenHelper->config.requireMigration:" + config.requireMigration);
    return null;
}

@NonNull
@Override
protected InvalidationTracker createInvalidationTracker() {
    Log.w(TAG_LOG, "->createInvalidationTracker is called.");
    return null;
}

@Override
public void clearAllTables() {
    Log.w(TAG_LOG, "->clearAllTables is called.");
}
}

日志猫：

2018-12-13 14:37:54.665 8949-8949 V/ActMain: ->initPersistentDBHandlerThread <-
2018-12-13 14:37:54.666 8949-8949 V/ActMain->RoomPersistentDBHandlerThread: RoomPersistentDBHandlerThread constructor is called.
2018-12-13 14:37:54.666 8949-8949 V/ActMain->RoomPersistentDBHandlerThread: initHandler is called
2018-12-13 14:37:54.667 8949-8967 V/ActMain->RoomPersistentDBHandlerThread: onLooperPrepared is called. [getLooper: Looper (ROOM_PERSISTENT_DB_HANDLER_THREAD, tid 356) {cbd0ffd}] ++++++++++++++++++++++++ 
2018-12-13 14:37:54.667 8949-8967 V/ActMain->RoomPersistentDBHandlerThread: ++++++++++++++++++++++++  [getLooper: Looper (ROOM_PERSISTENT_DB_HANDLER_THREAD, tid 356) {cbd0ffd}] ++++++++++++++++++++++++ 
2018-12-13 14:37:54.670 8949-8949 V/ActMain->RoomPersistentDBHandlerThread: enqueueMessage is called for what = 1
2018-12-13 14:37:54.670 8949-8967 V/ActMain->RoomPersistentDBHandlerThread: handleMessage is called for msg.what = 1
2018-12-13 14:37:54.670 8949-8967 V/ActMain: ->buildPersistentDB <-
2018-12-13 14:37:54.673 8949-8967 W/MovieDatabase: ->MovieDatabase constructor is called. <-
2018-12-13 14:37:54.673 8949-8967 W/MovieDatabase: ->init is called. <-
2018-12-13 15:02:54.802 9384-9403 D/ActMain->buildPersistentDB: ->this.mMovieDatabase.isOpen(): false

Answer 1

没有调用OnCreate的原因是因为它只在第一次创建数据库时调用一次，然后只要数据库存在就不会再调用。

如果您删除应用程序的数据或卸载应用程序然后重新运行它，您将看到然后调用onCreate。

例如

private void BuildDatabase() {
   RoomDatabase.Builder roombuilder = Room.databaseBuilder(this, Database.class,"mydb");
   roombuilder.addCallback(new RoomDatabase.Callback() {
       @Override
       public void onCreate(@NonNull SupportSQLiteDatabase db) {
           super.onCreate(db);
           Log.d("ONCREATE","Database has been created.");
       }

       @Override
       public void onOpen(@NonNull SupportSQLiteDatabase db) {
           super.onOpen(db);
           Log.d("ONOPEN","Database has been opened.");
       }
   });
   mRoomDB = (Database) roombuilder.build();
}

删除应用程序的数据结果后：-

2018-12-20 06:36:23.045 2271-2287/so53839431.so53839431roomrelationship D/ONCREATE: Database has been created.
2018-12-20 06:36:23.055 2271-2287/so53839431.so53839431roomrelationship D/ONOPEN: Database has been opened.

Answer 2

Oncreate创建数据库后将调用该方法。Room数据库是SQLiteOpenHelper的抽象。调用 getReadableDatabase() 或 getWriteableDatabase() 时创建的数据库。因此，直到执行一些具体操作，例如调用命中数据库的@Dao方法，数据库才会被创建。

要解决该问题，您应该应用以下选项之一。

• 执行一些操作，包括@delete、@insert 或@update

  或者

• 卸载应用程序之前，请删除手机设置中的应用程序数据

  或者

• 手动删除数据库文件（com.company.yourappAndroid Studio 上的设备文件资源管理器 → 数据 → 数据 → → 数据库）。

  或者

• 在您的项目中调用以下代码：

  public void deleteDatabaseFile(String databaseName) { 
              File databases = 
                     new File(getApplicationInfo().dataDir + "/databases");
              File db = new File(databases, databaseName);
  
              if (db.delete())
                  Timber.d("Database deleted successfully");
              else
                  Timber.d("Failed to delete database");
          }