android - 房间 : Database not created

Question

我尝试使用来自谷歌架构的房间库。我基于来自谷歌的 BasicSample 编写了一些代码，但没有创建数据库(对于我的代码)。 Logcat 不包含错误和异常。请帮我找出我的错误:

//App.java
//...
public class App extends Application {
    private AppExecutors mAppExecutors;
    private static final String TAG = "App";

    @Override
    public void onCreate() {
        super.onCreate();
        Log.i(TAG, "onCreate: enter");
        mAppExecutors = new AppExecutors();
        getDatabase();
    }

    public AppDatabase getDatabase() {
        return AppDatabase.getInstance(this, mAppExecutors);
    }
}

我的 AppDatabase 类看起来:

//AppDatabase.java
//...
@Database(entities = {Camera.class}, version = 1)
public abstract class AppDatabase extends RoomDatabase {
    private static final String DATABASE_NAME = "mydatabase";
    private static AppDatabase sInstance;
    private AppExecutors mExecutors;
    public abstract CameraDao cameraModel();

    public static AppDatabase getInstance(final Context context, final AppExecutors executors) {
        if (sInstance == null) {
            synchronized (AppDatabase.class) {
                if (sInstance == null) {
                    sInstance = buildDatabase(context.getApplicationContext(), executors);
                }
            }
        }
        return sInstance;
    }
    private static final String TAG = "AppDatabase";
    private static AppDatabase buildDatabase(final Context context, final AppExecutors executors) {
        Log.i(TAG, "buildDatabase: enter");
        AppDatabase database = Room.databaseBuilder(context, AppDatabase.class, DATABASE_NAME)
                .addCallback(new Callback() {

                    @Override
                    public void onCreate(@NonNull SupportSQLiteDatabase db) {
                        Log.i(TAG, "onCreate: ");
                        super.onCreate(db);

                        executors.diskIO().execute(() -> getInstance(context, executors).initDb());
                    }
                })
                .build();
        database.mExecutors = executors;
        Log.i(TAG, "buildDatabase: exit");
        return database;
    }

    private void initDb() {
        cameraModel().insert(new Camera(1, "Canon", "EOS 5d Mark III", 1024, 768, 24, 22, 0.0, true));
    }
}

道接口(interface):

//CameraDao.java
@Dao
public interface CameraDao {
    @Insert
    void insert(Camera camera);
}

和实体类:

// Camera.java
@Entity
public class Camera {
    @PrimaryKey(autoGenerate = true)
    public long id;
    public String list_name;
    public String camera_name;
    public int max_resolution_width;
    public int max_resolution_height;
    public int max_sensor_width;
    public int max_sensor_height;
    public double coc;
    public boolean is_auto_coc;

    public Camera(long id, String list_name, String camera_name, int max_resolution_width, int max_resolution_height, int max_sensor_width, int max_sensor_height, double coc, boolean is_auto_coc) {
        this.id = id;
        this.list_name = list_name;
        this.camera_name = camera_name;
        this.max_resolution_width = max_resolution_width;
        this.max_resolution_height = max_resolution_height;
        this.max_sensor_width = max_sensor_width;
        this.max_sensor_height = max_sensor_height;
        this.coc = coc;
        this.is_auto_coc = is_auto_coc;
    }

    @Ignore
    public Camera(String list_name, String camera_name, int max_resolution_width, int max_resolution_height, int max_sensor_width, int max_sensor_height, double coc, boolean is_auto_coc) {
        this.list_name = list_name;
        this.camera_name = camera_name;
        this.max_resolution_width = max_resolution_width;
        this.max_resolution_height = max_resolution_height;
        this.max_sensor_width = max_sensor_width;
        this.max_sensor_height = max_sensor_height;
        this.coc = coc;
        this.is_auto_coc = is_auto_coc;
    }
}

因此，无法使用此代码创建数据库。未调用创建数据库的回调。顺便说一句，如果我有自动增量字段，是否可以插入自定义值(针对特殊情况)。

我的这段代码的 logcat:

12-04 00:54:47.536 9150-9150/ru.neverdark.photonotes I/App: onCreate: enter

12-04 00:54:47.537 9150-9150/ru.neverdark.photonotes I/AppDatabase: buildDatabase: enter

12-04 00:54:47.541 9150-9150/ru.neverdark.photonotes I/AppDatabase: buildDatabase: exit

Answer 1

在幕后，默认情况下，Room 使用 SQLiteOpenHelper，就像您可以直接使用它一样。

当您创建 SQLiteOpenHelper 实例时，

SQLiteOpenHelper 不会创建数据库。一旦您调用 getReadableDatabase() 或 getWriteableDatabase()，它就会这样做。

从 Room 的角度来看，这意味着直到您执行一些具体的操作，例如调用访问数据库的 @Dao 方法，您的数据库才会被创建。