My app database class
@Database(entities = {Detail.class}, version = Constant.DATABASE_VERSION)
public abstract class AppDatabase extends RoomDatabase {
I met this problem because I have forgotten the apt dependences
implementation "android.arch.lifecycle:extensions:$archLifecycleVersion"
implementation "android.arch.persistence.room:runtime:$archRoomVersion"
annotationProcessor "android.arch.lifecycle:compiler:$archLifecycleVersion"
annotationProcessor "android.arch.persistence.room:compiler:$archRoomVersion"
after added the annotationProcessor, and rebuild it, the problem solved.