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（）首次创建数据库并创建所有表后调用。

我调用buildPersistentDB（）之后发生的事情是，我从MoviesDatabase类收到了日志，该类使用@Database进行了注释，但是RoomDatabase.Callback中的onCreate（）日志是我打过电话就没打过电话

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

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

我想知道为什么尽管成功创建了数据库，但Room.Callback中的onCreate（）方法没有收到日志

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.");
}
}

logcat ：

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

之所以没有调用 OnCreate 的原因是，它仅在第一次创建数据库时被调用一次，然后只要该数据库存在就不再调用。

如果您删除该应用程序的数据或卸载该应用程序，然后重新运行它，您将看到随后调用 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后，结果为：-

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

创建数据库后，将调用

Oncreate方法。会议室数据库是SQLiteOpenHelper的抽象。调用getReadableDatabase（）或getWriteableDatabase（）时创建的数据库。因此，在执行某些具体操作之前，例如调用命中数据库的@Dao方法，将不会创建数据库。

要解决此问题，您应该应用以下选项之一。

执行一些操作，包括@ delete，@ insert或@update

或
在卸载应用程序之前删除手机设置中的应用程序数据

或
手动删除数据库文件（设备文件资源管理器→数据→数据→com.company.yourapp→Android Studio上的数据库）。

或

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");
        }

成功调用.build（）

2 个答案: