[英]How to pre-populate data in Room Database
我正在通过 Java 教程开发联系人应用程序。 我能够将转换转换为 Kotlin,直到我开始遇到 AsyncTask 问题来预填充数据。
我确认我可以将数据从活动发送到 Room 数据库,但似乎没有来自预先填充的数据。
数据库
@Database(entities = [ContactEntity::class], version = 1, exportSchema = false)
abstract class ContactDatabase : RoomDatabase() {
abstract fun getContactDao():ContactDao
companion object{
private var instance:ContactDatabase?=null
@kotlin.UseExperimental(InternalCoroutinesApi::class)
fun getInstance(context: Context): ContactDatabase {
return instance?: synchronized(this){
instance?: Room.databaseBuilder(context.applicationContext,
ContactDatabase::class.java, "contact_database")
.fallbackToDestructiveMigration()
.addCallback(roomCallBack)
.build()
}
}
val roomCallBack = object: RoomDatabase.Callback(){
override fun onCreate(db: SupportSQLiteDatabase) {
super.onCreate(db)
instance?.let { PopulateDbAsyncTask(it).execute() }
}
}
internal class PopulateDbAsyncTask(db: ContactDatabase) : AsyncTask<Void, Void, Void>(){
val contactDao = db.getContactDao()
override fun doInBackground(vararg p0: Void?): Void? {
contactDao.insert(ContactEntity("Darot", "Tosin", "M", "Atlantic View", "08060085192", R.drawable.maleavatar))
contactDao.insert(ContactEntity("Tola", "Folawo", "M", "Atlantic View", "08060085192", R.drawable.femaleavatar))
contactDao.insert(ContactEntity("Aisha", "Monday", "M", "Atlantic View", "08060085192", R.drawable.femaleavatar))
return null
}
}
}
}
主要活动
class MainActivity : AppCompatActivity() {
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
// val contacts:ArrayList<ContactEntity>
val contacts = arrayOf(
ContactEntity("Tola", "Folawo", "M", "Atlantic View", "08060085192", R.drawable.femaleavatar),
ContactEntity("Aisha", "Monday", "M", "Atlantic View", "08060085192", R.drawable.femaleavatar),
ContactEntity("Darot", "Tosin", "M", "Atlantic View", "08060085192", R.drawable.maleavatar)
)
val arrayList: ArrayList<String> = ArrayList<String>(5)
var list: MutableList<ContactEntity> = mutableListOf<ContactEntity>()
list.add(ContactEntity("Tola", "Folawo", "M", "Atlantic View", "08060085192", R.drawable.femaleavatar))
list.add(ContactEntity("Aisha", "Monday", "M", "Atlantic View", "08060085192", R.drawable.femaleavatar))
list.add(ContactEntity("Darot", "Tosin", "M", "Atlantic View", "08060085192", R.drawable.maleavatar))
val contactList = ArrayList<ContactEntity>()
contactList.addAll(list)
recyclerView.layoutManager = LinearLayoutManager(this)
recyclerView.setHasFixedSize(true)
val adapter = ContactAdapter()
recyclerView.adapter = adapter
val contactViewModel = ViewModelProviders.of(this).get(ContactViewModel::class.java)
contactViewModel.getAllContactsModel().observe(this, object:Observer<List<ContactEntity>>{
override fun onChanged(t: List<ContactEntity>) {
adapter.setContacts(t)
Toast.makeText(applicationContext, "$t", Toast.LENGTH_LONG).show()
}
})
}
}
从上面的代码中,我可以手动将数据填充到数据库中。 我哪里做错了?
除非读取或写入表,否则不会命中房间回调。 所以做“.build”从来没有真正命中回调。 因此,对此的一个简单解决方案是在构建表后直接开始和结束事务。
db.beginTransaction()
db.endTransaction()
这是一个类似堆栈溢出问题的链接,可以帮助您: Room Database force OnCreate callback
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