JetPack Room 入门使用完整示例

具体数据可以参考官方文档：https://developer.android.com/codelabs/kotlin-android-training-room-database?hl=zh-cn#0

第一步：导入依赖

1、插件

plugins {
    id("com.android.application")
    id("org.jetbrains.kotlin.android")
    id("kotlin-kapt")
}

2、依赖

implementation("androidx.room:room-runtime:2.6.1")
annotationProcessor("androidx.room:room-compiler:2.6.1")
implementation("androidx.room:room-ktx:2.6.1")
kapt("androidx.room:room-compiler:2.6.1")

版本问题（可能存在）

    compileOptions {
        //JavaVersion.VERSION_1_8这个版本可能不兼容，根据环境的版本来更换
        sourceCompatibility = JavaVersion.VERSION_17 
        targetCompatibility = JavaVersion.VERSION_17
    }
    kotlinOptions {
        jvmTarget = "17"
    }

二、定义实体类

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

@Entity(tableName = "daily_sleep_quality_table")
data class SleepNight(

    @PrimaryKey(autoGenerate = true)
    var nightId: Long = 0L,

    @ColumnInfo(name = "start_time_milli")
    val startTimeMilli: Long = System.currentTimeMillis(),

    @ColumnInfo(name = "end_time_milli")
    var endTimeMilli: Long = startTimeMilli,

    @ColumnInfo(name = "quality_rating")
    var sleepQuality: Int = -1
)

三、定义Dao访问类

import androidx.lifecycle.LiveData
import androidx.room.Dao
import androidx.room.Insert
import androidx.room.Query
import androidx.room.Update

@Dao
interface SleepDatabaseDao {

    @Insert
    fun insert(night: SleepNight)

    @Update
    fun update(night: SleepNight)

    @Query("SELECT * from daily_sleep_quality_table WHERE nightId = :key")
    fun get(key: Long): SleepNight?


    @Query("DELETE FROM daily_sleep_quality_table")
    fun clear()

    @Query("SELECT * FROM daily_sleep_quality_table ORDER BY nightId DESC LIMIT 1")
    fun getTonight(): SleepNight?

    @Query("SELECT * FROM daily_sleep_quality_table ORDER BY nightId DESC")
    fun getAllNights(): LiveData<List<SleepNight>>

四、定义DataBase操作类

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

@Database(entities = [SleepNight::class], version = 1, exportSchema = false)
abstract class SleepDatabase : RoomDatabase() {

    abstract val sleepDatabaseDao: SleepDatabaseDao

    companion object {

        @Volatile
        private var INSTANCE: SleepDatabase? = null

        fun getInstance(context: Context): SleepDatabase {
            synchronized(this) {
                var instance = INSTANCE

                if (instance == null) {
                    instance = Room.databaseBuilder(
                        context.applicationContext,
                        SleepDatabase::class.java,
                        "sleep_history_database"
                    )
                        .fallbackToDestructiveMigration()
                        .build()
                    INSTANCE = instance
                }
                return instance
            }
        }
    }
}

五、使用（必须在子线程中或者协程中使用）

在项目中我们一般是结合LiveData和ViewModel一起使用。

class MainActivity2 : ComponentActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)

        setContent {
            MyApplicationTheme {
                GetMessage(this)
            }
        }
    }
}

@Composable
fun GetMessage(mainActivity2: MainActivity2) {
    Column {
        Button(onClick = {
            GlobalScope.launch{
                try {
                    SleepDatabase.getInstance(mainActivity2)
                        .sleepDatabaseDao
                        .insert(SleepNight())
                }catch (e:Exception){
                    Log.e("Xiang","出现了错误：${e.message}")
                }
            }
        }) {
            Text(text = "添加数据")
        }
    }
}

六、利用Android Studio工具查看

打开菜单【view】->【Tool Windows】->【App Inspection】