Question

我正在应用程序中设置房间数据库，我想从在自定义表面视图上绘图的用户那里获取数据。

应用程序使用MVVM模式在Android 9上运行，我尝试了不带Room的应用程序，并且该应用程序正常运行。实施Room后，应用不再观察数据更改。我使用google codelabs作为我的应用程序的模板。用户通过单击视图在表面视图上绘制图形的节点，我想将place（节点）的数据存储在数据库中。

地点：

@Entity(tableName = "places")
data class Place(
        @Embedded
        var mPosition: Point,

        @PrimaryKey(autoGenerate = false)
        @ColumnInfo(name = "place_id")
        var mID: Int = -1,

        @ColumnInfo(name = "name")
        override var mName: String = "",

        @ColumnInfo(name = "tokens")
        var mTokens: Int = 0
) : Node() {

    override fun isValid(): Boolean {
        return mID == -1 && mPosition.x != 0f && mPosition.y != 0f && mTokens >= 0
    }
}

PlaceDao：

@Dao
interface PlaceDao {

    @Insert
    fun addPlace(place: Place)

    @Query("SELECT * FROM places ORDER BY place_id ASC")
    fun getPlaces(): LiveData<List<Place>>
    ...
}

数据库：

@Database(entities = [Place::class, Transition::class, Arc::class], version = 1)
@TypeConverters(Converter::class)
abstract class AppRoomDatabase : RoomDatabase() {

    abstract fun placeDao(): PlaceDao

companion object {
        @Volatile
        private var INSTANCE: AppRoomDatabase? = null

        fun getDatabase(
                context: Context,
                scope: CoroutineScope
        ): AppRoomDatabase {
            return INSTANCE ?: synchronized(this) {
                val instance = Room.databaseBuilder(
                        context.applicationContext,
                        AppRoomDatabase::class.java,
                        "word_database"
                )
                        .fallbackToDestructiveMigration()
                        .addCallback(AppDatabaseCallback(scope))
                        .build()
                INSTANCE = instance
                instance
            }
        }
        private class AppDatabaseCallback(
                private val scope: CoroutineScope
        ) : RoomDatabase.Callback() {
            override fun onOpen(db: SupportSQLiteDatabase) {
                super.onOpen(db)
                INSTANCE?.let { database ->
                    scope.launch(Dispatchers.IO) {
                        populateDatabase(database.placeDao(),database.transitionDao(),database.arcDao())
                    }
                }
            }
        }
    }
}

存储库：

class NetRepositoryImpl(
        private val placeDao: PlaceDao,
        private val transitionDao: TransitionDao,
        private val arcDao: ArcDao
) : NetRepository {
    @WorkerThread
    override suspend fun addPlace(place: Place) {
        placeDao.addPlace(place)
    }

    override fun getPlaces() = placeDao.getPlaces()
}

ViewModel：

class NetViewModel(application: Application) : AndroidViewModel(application) {

    private var parentJob = Job()
    private val coroutineContext: CoroutineContext
        get() = parentJob + Dispatchers.Main
    private val scope = CoroutineScope(coroutineContext)

    private val netRepository: NetRepositoryImpl

    val allPlaces: LiveData<List<Place>>
    ...

init {
        val placeDao = AppRoomDatabase.getDatabase(application, scope).placeDao()
    ...
    netRepository = NetRepositoryImpl(placeDao, transitionDao, arcDao)       
    allPlaces = netRepository.getPlaces()
    ...
}

fun addPlace(place: Place) {
        if (place.isValid())
            scope.launch(Dispatchers.IO) { netRepository.addPlace(place) }
    }

活动：

class EditorActivity : FragmentActivity() {
    private lateinit var viewModel: NetViewModel

    override fun onCreate(savedInstanceState: Bundle?) {
        ...

        viewModel = ViewModelProviders.of(this).get(NetViewModel::class.java)

        viewModel.apply {
            allPlaces.observe(this@EditorActivity, Observer { places ->
                editorDrawer.mPlaces = places
                Log.d("Editor activity", "Places observed")
            })
        ...
        editorDrawer.setOnTouchListener { v, event ->
            when (event?.action) {
                MotionEvent.ACTION_DOWN -> {
            ...
            viewModel.addPlace(Point(event.x, event.y))
            ...
            }
        }
        ...
}

editorDrawer是活动布局中的自定义表面视图。

当用户单击表面视图时，我希望创建一个新的位置并将其存储在数据库中，然后在更改数据时在表面视图上绘制它，创建了新的位置实例，但未存储并且未观察到任何更改，因此没有位置画。我可以在控制台日志中找到

"Places observed"

仅在应用启动时，就像数据完全不变一样……

Answer 1

好问题与Room或MVVM模式无关，这是我粗心大意的副产品...如果地方实体类的isValid（）函数中的条件存在错误，则发生错误...

return mID == -1 && mPosition.x != 0f && mPosition.y != 0f && mTokens >= 0

到

return mID != -1 && mPosition.x != 0f && mPosition.y != 0f && mTokens >= 0

如何观察从自定义曲面视图生成的数据

1 个答案: