我试图创建一个数据库来存储抽认卡使用房间。我确信我已经完成了所有必要的代码，但是，当我运行我的应用程序并使用数据库检查器时，它说没有什么可显示的。我不知道为什么任何帮助将不胜感激。

实体

import androidx.room.Entity
import androidx.room.PrimaryKey

@Entity(tableName = "flashcards")
data class Flashcard(
    @PrimaryKey(autoGenerate = true)
    val id: Int = 0,
    val question: String,
    val answer: String
)

数据访问对象

import androidx.room.Dao
import androidx.room.Delete
import androidx.room.Insert
import androidx.room.OnConflictStrategy
import androidx.room.Query
import androidx.room.Update
import kotlinx.coroutines.flow.Flow
@Dao
interface FlashcardDao {
    @Insert(onConflict = OnConflictStrategy.IGNORE)
    suspend fun insert(flashcard: Flashcard)

    @Update
    suspend fun update(flashcard: Flashcard)

    @Delete
    suspend fun delete(flashcard: Flashcard)

    @Query("SELECT * FROM flashcards WHERE id = :id")
    fun getFlashcard(id: Int): Flow<Flashcard>

    @Query("SELECT * FROM flashcards")
    fun getAllFlashcards(): Flow<List<Flashcard>>

}

数据库类

import android.content.Context
import androidx.room.Database
import androidx.room.Room
import androidx.room.RoomDatabase

@Database(
    entities = [Flashcard::class],
    version = 1,
    exportSchema = false
)
abstract class FlashcardDatabase: RoomDatabase() {
    abstract fun flashcardDao(): FlashcardDao

    companion object {
        @Volatile
        private var Instance: FlashcardDatabase? = null
        fun getDatabase(context: Context): FlashcardDatabase {
            return Instance ?: synchronized(this) {
                Room.databaseBuilder(context, FlashcardDatabase::class.java, "flashcard_database")
                    .fallbackToDestructiveMigration()
                    .build()
                    .also { Instance = it }
            }
        }
    }
}

仓库接口

interface FlashCardsRepository {
    fun getAllFlashcardsStream(): Flow<List<Flashcard>>
    fun getFlashcardStream(id: Int): Flow<Flashcard?>
    suspend fun insertFlashcard(flashcard: Flashcard)
    suspend fun deleteFlashcard(flashcard: Flashcard)
    suspend fun updateFlashcard(flashcard: Flashcard)

}

仓库实现类

import kotlinx.coroutines.flow.Flow

class OfflineFlashcardsRepository(private val flashcardDao: FlashcardDao) : FlashCardsRepository {
    override fun getAllFlashcardsStream(): Flow<List<Flashcard>> = flashcardDao.getAllFlashcards()
    override fun getFlashcardStream(id: Int): Flow<Flashcard?> = flashcardDao.getFlashcard(id)
    override suspend fun insertFlashcard(flashcard: Flashcard) = flashcardDao.insert(flashcard = flashcard)
    override suspend fun updateFlashcard(flashcard: Flashcard) = flashcardDao.update(flashcard = flashcard)
    override suspend fun deleteFlashcard(flashcard: Flashcard) = flashcardDao.delete(flashcard = flashcard)

}

App容器（用于依赖注入）

import android.content.Context

interface AppContainer {
    val flashCardsRepository: FlashCardsRepository
}

class AppDataContainer(private val context: Context): AppContainer {
    override val flashCardsRepository: FlashCardsRepository by lazy {
        OfflineFlashcardsRepository(FlashcardDatabase.getDatabase(context).flashcardDao())
    }

}

创建数据库示例onCreate（）的Flashcard应用程序（我已经将此应用程序添加到清单文件中）

import android.app.Application
import com.example.flashcardapp.data.AppContainer
import com.example.flashcardapp.data.AppDataContainer

class FlashcardApplication: Application() {
    lateinit var container: AppContainer
    override fun onCreate() {
        super.onCreate()
        container = AppDataContainer(this)
    }
}

清单文件

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools">

    <application
        android:name=".FlashcardApplication"
        android:allowBackup="true"
        android:dataExtractionRules="@xml/data_extraction_rules"
        android:fullBackupContent="@xml/backup_rules"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:roundIcon="@mipmap/ic_launcher_round"
        android:supportsRtl="true"
        android:theme="@style/Theme.FlashcardApp"
        tools:targetApi="31">
        <activity
            android:name=".MainActivity"
            android:exported="true"
            android:label="@string/app_name"
            android:theme="@style/Theme.FlashcardApp">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>

数据库检查器显示的内容