Android kotlin+协程+Room数据库的简单使用
Room
Room是Google为了简化旧版的SQLite操作专门提供的
1.拥有了SQLite的所有操作功能
2.使用简单（类似于Retrofit），通过注解的方式实现相关功能。编译时自动生成实现类impl
3.LiveData，LifeCycle，Paging天然融合支持
导入
...
plugins{
id'com.android.application'
id'kotlin-android'
id'kotlin-android-extensions'
id'kotlin-kapt'
}
dependencies{
//room数据库
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"//CoroutinessupportforRoom协程操作库
//lifecycle
implementation'androidx.lifecycle:lifecycle-extensions:2.2.0'
implementation'androidx.lifecycle:lifecycle-runtime-ktx:2.2.0'
}
User
packagecom.zhangyu.myroom.data importandroid.os.Parcelable importandroidx.room.Entity importandroidx.room.PrimaryKey importkotlinx.android.parcel.Parcelize @Parcelize @Entity(tableName="User") dataclassUser( @PrimaryKey varid:String, varname:String ):Parcelable
UserDao
packagecom.zhangyu.myroom.data
importandroidx.room.*
@Dao
interfaceUserDao{
@Insert(onConflict=OnConflictStrategy.REPLACE)
funputUser(cacheBean:User)
@Query("select*fromUserwhereid=:id")
suspendfungetUser(id:String):User?
@Query("select*fromUser")
suspendfungetAllUser():List?
@Delete
fundelete(user:User)
@Update(onConflict=OnConflictStrategy.REPLACE)
funupdate(user:User)
}
UserDatabase
packagecom.zhangyu.myroom.data
importandroid.util.Log
importandroidx.room.Database
importandroidx.room.Room
importandroidx.room.RoomDatabase
importandroidx.sqlite.db.SupportSQLiteDatabase
importcom.zhangyu.myroom.App
privateconstvalTAG="CacheDataBase"
//后续的数据库升级是根据这个version来比较的，exportSchema导出架构
@Database(entities=[User::class],version=1,exportSchema=false)
abstractclassUserDatabase:RoomDatabase(){
companionobject{
vardataBase:UserDatabase
init{
//如果databaseBuilder改为inMemoryDatabaseBuilder则创建一个内存数据库（进程销毁后，数据丢失）
dataBase=Room.databaseBuilder(App.context,UserDatabase::class.java,"db_user")
//是否允许在主线程进行查询
.allowMainThreadQueries()
//数据库创建和打开后的回调，可以重写其中的方法
.addCallback(object:Callback(){
overridefunonCreate(db:SupportSQLiteDatabase){
super.onCreate(db)
Log.d(TAG,"onCreate:db_user")
}
})
//数据库升级异常之后的回滚
.fallbackToDestructiveMigration()
.build()
}
}
abstractfungetUserDao():UserDao
}
MainActivity
packagecom.zhangyu.myroom
importandroid.os.Bundle
importandroid.util.Log
importandroidx.appcompat.app.AppCompatActivity
importandroidx.lifecycle.lifecycleScope
importcom.zhangyu.myroom.data.User
importcom.zhangyu.myroom.data.UserDatabase
importkotlinx.coroutines.launch
privateconstvalTAG="MainActivity"
classMainActivity:AppCompatActivity(){
overridefunonCreate(savedInstanceState:Bundle?){
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
testCache()
}
privatefuntestCache(){
valuserDao=UserDatabase.dataBase.getUserDao()
userDao.putUser(User("1001","zhangyu"))
userDao.putUser(User("1002","liming"))
lifecycleScope.launch{
valusers=userDao.getAllUser()
Log.e(TAG,"users:$users")
valuser=userDao.getUser("1001")
Log.e(TAG,"user:$user")
Log.e(TAG,"testCache:协程执行完毕")
}
Log.e(TAG,"testCache:")
}
}
结果
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:协程执行完毕
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