以数据库创建为例
在Java中
@Database(entities = {User.class}, version = 1)
public abstract class UsersDatabase extends RoomDatabase {
private static volatile UsersDatabase INSTANCE;
public abstract UserDao userDao();
public static UsersDatabase getInstance(Context context) {
if (INSTANCE == null) {
synchronized (UsersDatabase.class) {
if (INSTANCE == null) {
INSTANCE = Room.databaseBuilder(context.getApplicationContext(),
UsersDatabase.class, "Sample.db")
.build();
}
}
}
return INSTANCE;
}
}
在Kotlin中
@Database(entities = arrayOf(User::class), version = 1)
abstract class UsersDatabase : RoomDatabase() {
abstract fun userDao(): UserDao
companion object {
@Volatile private var INSTANCE: UsersDatabase? = null
fun getInstance(context: Context): UsersDatabase =
INSTANCE ?: synchronized(this) {
INSTANCE ?: buildDatabase(context).also { INSTANCE = it }
}
private fun buildDatabase(context: Context) =
Room.databaseBuilder(context.applicationContext,
UsersDatabase::class.java, "Sample.db")
.build()
}
}
