Room

Room是Google為了簡化舊版的SQLite操作專門提供的1.擁有了SQLite的所有操作功能2.使用簡單（類似于Retrofit），通過注解的方式實現相關功能。編譯時自動生成實現類impl3.LiveData，LifeCycle，Paging天然融合支持

導入

...plugins { id ’com.android.application’ id ’kotlin-android’ id ’kotlin-android-extensions’ id ’kotlin-kapt’}dependencies { //room數據庫 implementation 'androidx.room:room-runtime:2.2.5' kapt 'androidx.room:room-compiler:2.2.5' // Kotlin 使用 kapt implementation 'androidx.room:room-ktx:2.2.5'//Coroutines support for Room 協程操作庫 //lifecycle implementation ’androidx.lifecycle:lifecycle-extensions:2.2.0’ implementation ’androidx.lifecycle:lifecycle-runtime-ktx:2.2.0’}

User

package com.zhangyu.myroom.dataimport android.os.Parcelableimport androidx.room.Entityimport androidx.room.PrimaryKeyimport kotlinx.android.parcel.Parcelize@Parcelize@Entity(tableName = 'User')data class User( @PrimaryKey var id: String, var name: String) : Parcelable

UserDao

package com.zhangyu.myroom.dataimport androidx.room.*@Daointerface UserDao { @Insert(onConflict = OnConflictStrategy.REPLACE) fun putUser(cacheBean: User) @Query('select * from User where id =:id') suspend fun getUser(id: String): User? @Query('select * from User') suspend fun getAllUser(): List<User>? @Delete fun delete(user: User) @Update(onConflict = OnConflictStrategy.REPLACE) fun update(user: User)}

UserDatabase

package com.zhangyu.myroom.dataimport android.util.Logimport androidx.room.Databaseimport androidx.room.Roomimport androidx.room.RoomDatabaseimport androidx.sqlite.db.SupportSQLiteDatabaseimport com.zhangyu.myroom.Appprivate const val TAG = 'CacheDataBase'//后續的數據庫升級是根據這個version來比較的，exportSchema導出架構@Database(entities = [User::class], version = 1, exportSchema = false)abstract class UserDatabase : RoomDatabase() { companion object { var dataBase: UserDatabase init { //如果databaseBuilder改為inMemoryDatabaseBuilder則創建一個內存數據庫（進程銷毀后，數據丟失） dataBase = Room.databaseBuilder(App.context, UserDatabase::class.java, 'db_user')//是否允許在主線程進行查詢.allowMainThreadQueries()//數據庫創建和打開后的回調，可以重寫其中的方法.addCallback(object : Callback() { override fun onCreate(db: SupportSQLiteDatabase) { super.onCreate(db) Log.d(TAG, 'onCreate: db_user') }})//數據庫升級異常之后的回滾.fallbackToDestructiveMigration().build() } } abstract fun getUserDao(): UserDao}

MainActivity

package com.zhangyu.myroomimport android.os.Bundleimport android.util.Logimport androidx.appcompat.app.AppCompatActivityimport androidx.lifecycle.lifecycleScopeimport com.zhangyu.myroom.data.Userimport com.zhangyu.myroom.data.UserDatabaseimport kotlinx.coroutines.launchprivate const val TAG = 'MainActivity'class MainActivity : AppCompatActivity() { override fun onCreate(savedInstanceState: Bundle?) { super.onCreate(savedInstanceState) setContentView(R.layout.activity_main) testCache() } private fun testCache() { val userDao = UserDatabase.dataBase.getUserDao() userDao.putUser(User('1001', 'zhangyu')) userDao.putUser(User('1002', 'liming')) lifecycleScope.launch { val users = userDao.getAllUser() Log.e(TAG, 'users: $users') val user = userDao.getUser('1001') Log.e(TAG, 'user: $user') Log.e(TAG, 'testCache: 協程執行完畢') } Log.e(TAG, 'testCache: ') }}

結果

E/MainActivity: testCache: E/MainActivity: users: [User(id=1001, name=zhangyu), User(id=1002, name=liming)]E/MainActivity: user: User(id=1001, name=zhangyu)E/MainActivity: testCache: 協程執行完畢

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