我的项目有一个回收站，该回收站将信息电影保存在文件中，并将收藏夹保存到数据库中。我使用了Room Database，但它返回了一个空对象引用：
import android.content.Context
import androidx.room.Database
import androidx.room.Room
import androidx.room.RoomDatabase
import com.example.week3.dao.MovieDao
import com.example.week3.model.movie
@Database(entities = [movie::class], version = 5,exportSchema = false)
abstract class AppDatabase : RoomDatabase() {
abstract fun movieDao():MovieDao
companion object {
@Volatile
private var INSTANCE: AppDatabase? = null
private val LOCK=Any()
private val DB_NAME = "movie_favorite_db"
operator fun invoke(context: Context)= INSTANCE?: synchronized(LOCK){
INSTANCE?: getDatabase(context).also {
INSTANCE=it
}
}
fun getDatabase(context: Context) = Room.databaseBuilder(
context.applicationContext,
AppDatabase::class.java,
DB_NAME
).allowMainThreadQueries()
.build() // alway return null
}
}
仓库呼叫室：
package com.example.week3.data
import android.app.Application
import com.example.week3.model.listMovieAndInfo
import com.example.week3.model.movie
import com.google.gson.Gson
import com.khtn.androidcamp.DataCenter
class dataRepositories(application:Application) {
val moviesDao = AppDatabase.invoke(application).movieDao()
val listMovieFavorite=moviesDao.getAllTasks()
fun getListMovie(): MutableList<movie> {
var listMovie= mutableListOf<movie>()
val gson=Gson();
val listMoiveIfo=gson.fromJson<listMovieAndInfo>(DataCenter.getMovieJsonString(),listMovieAndInfo::class.java);
if (listMoiveIfo.total_pages>0){
listMovie=listMoiveIfo.results
}
return listMovie
}
suspend fun deleteMovieFavorite(movie: movie){
moviesDao.deleteMovie(movie)
}
suspend fun insertMovieFavorite(movie: movie){
moviesDao.insertMovie(movie)
}
}
我观察到一个片段：
package com.example.week3.view
import android.content.Intent
import android.os.Bundle
import androidx.fragment.app.Fragment
import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup
import androidx.lifecycle.ViewModelProvider
import androidx.recyclerview.widget.GridLayoutManager
import com.example.week3.R
import com.example.week3.adapter.rv_adapter
import com.example.week3.data.dataRepositories
import com.example.week3.model.movie
import com.example.week3.viewmodel.MovieViewModel
import kotlinx.android.synthetic.main.fragment_now_playing.*
class NowPlayingFragment : Fragment() {
private lateinit var movieFavoriteViewModel: MovieViewModel
var listMovie = listOf<movie>()
var rv_layoutManager= GridLayoutManager(activity,1)
var rv_adapter_list_film= rv_adapter(listMovie,rv_layoutManager);
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
}
override fun onCreateView(
inflater: LayoutInflater, container: ViewGroup?,
savedInstanceState: Bundle?
): View? {
// Inflate the layout for this fragment
return inflater.inflate(R.layout.fragment_now_playing, container, false)
}
override fun onActivityCreated(savedInstanceState: Bundle?) {
super.onActivityCreated(savedInstanceState)
setContent()
}
private fun setContent() {
movieFavoriteViewModel= ViewModelProvider(this).get(MovieViewModel::class.java)
listMovie=movieFavoriteViewModel.listAllMovie
setRecyclerView()
}
private fun setRecyclerView() {
rv_list_film_now_playing.layoutManager=rv_layoutManager
rv_list_film_now_playing.adapter=rv_adapter_list_film
rv_adapter_list_film.listener=object :rv_adapter.OnItemClickListener{
override fun onItemClick(item: movie) {
val intent= Intent(activity,filmDetailActivity::class.java);
//intent.putExtra("film_detail",item)
startActivity(intent)
}
override fun onStartItemToggle(item: movie) {
}
}
}
}
这是我在运行时遇到的错误：
D/AndroidRuntime: Shutting down VM
E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.week3, PID: 15927
java.lang.RuntimeException: Cannot create an instance of class com.example.week3.viewmodel.MovieViewModel
at androidx.lifecycle.ViewModelProvider$AndroidViewModelFactory.create(ViewModelProvider.java:275)
at androidx.lifecycle.SavedStateViewModelFactory.create(SavedStateViewModelFactory.java:106)
at androidx.lifecycle.ViewModelProvider.get(ViewModelProvider.java:185)
at androidx.lifecycle.ViewModelProvider.get(ViewModelProvider.java:150)
at com.example.week3.view.NowPlayingFragment.setContent(NowPlayingFragment.kt:45)
at com.example.week3.view.NowPlayingFragment.onActivityCreated(NowPlayingFragment.kt:40)
at androidx.fragment.app.Fragment.performActivityCreated(Fragment.java:2717)
at androidx.fragment.app.FragmentStateManager.activityCreated(FragmentStateManager.java:336)
at androidx.fragment.app.FragmentManager.moveToState(FragmentManager.java:1186)
at androidx.fragment.app.FragmentManager.moveToState(FragmentManager.java:1354)
at androidx.fragment.app.FragmentManager.moveFragmentToExpectedState(FragmentManager.java:1432)
at androidx.fragment.app.FragmentManager.moveToState(FragmentManager.java:1495)
at androidx.fragment.app.BackStackRecord.executeOps(BackStackRecord.java:447)
at androidx.fragment.app.FragmentManager.executeOps(FragmentManager.java:2167)
at androidx.fragment.app.FragmentManager.executeOpsTogether(FragmentManager.java:1990)
at androidx.fragment.app.FragmentManager.removeRedundantOperationsAndExecute(FragmentManager.java:1945)
at androidx.fragment.app.FragmentManager.execPendingActions(FragmentManager.java:1847)
at androidx.fragment.app.FragmentManager$4.run(FragmentManager.java:413)
at android.os.Handler.handleCallback(Handler.java:883)
at android.os.Handler.dispatchMessage(Handler.java:100)
at android.os.Looper.loop(Looper.java:237)
at android.app.ActivityThread.main(ActivityThread.java:7860)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1075)
Caused by: java.lang.reflect.InvocationTargetException
at java.lang.reflect.Constructor.newInstance0(Native Method)
at java.lang.reflect.Constructor.newInstance(Constructor.java:343)
at androidx.lifecycle.ViewModelProvider$AndroidViewModelFactory.create(ViewModelProvider.java:267)
at androidx.lifecycle.SavedStateViewModelFactory.create(SavedStateViewModelFactory.java:106)
at androidx.lifecycle.ViewModelProvider.get(ViewModelProvider.java:185)
at androidx.lifecycle.ViewModelProvider.get(ViewModelProvider.java:150)
at com.example.week3.view.NowPlayingFragment.setContent(NowPlayingFragment.kt:45)
at com.example.week3.view.NowPlayingFragment.onActivityCreated(NowPlayingFragment.kt:40)
at androidx.fragment.app.Fragment.performActivityCreated(Fragment.java:2717)
at androidx.fragment.app.FragmentStateManager.activityCreated(FragmentStateManager.java:336)
at androidx.fragment.app.FragmentManager.moveToState(FragmentManager.java:1186)
at androidx.fragment.app.FragmentManager.moveToState(FragmentManager.java:1354)
at androidx.fragment.app.FragmentManager.moveFragmentToExpectedState(FragmentManager.java:1432)
at androidx.fragment.app.FragmentManager.moveToState(FragmentManager.java:1495)
at androidx.fragment.app.BackStackRecord.executeOps(BackStackRecord.java:447)
at androidx.fragment.app.FragmentManager.executeOps(FragmentManager.java:2167)
at androidx.fragment.app.FragmentManager.executeOpsTogether(FragmentManager.java:1990)
at androidx.fragment.app.FragmentManager.removeRedundantOperationsAndExecute(FragmentManager.java:1945)
at androidx.fragment.app.FragmentManager.execPendingActions(FragmentManager.java:1847)
at androidx.fragment.app.FragmentManager$4.run(FragmentManager.java:413)
at android.os.Handler.handleCallback(Handler.java:883)
at android.os.Handler.dispatchMessage(Handler.java:100)
at android.os.Looper.loop(Looper.java:237)
at android.app.ActivityThread.main(ActivityThread.java:7860)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1075)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String java.lang.Package.getName()' on a null object reference
at androidx.room.Room.getGeneratedImplementation(Room.java:79)
at androidx.room.RoomDatabase$Builder.build(RoomDatabase.java:952)
at AppDatabase$Companion.getDatabase(AppDatabase.kt:26)
at AppDatabase$Companion.invoke(AppDatabase.kt:17)
at com.example.week3.data.dataRepositories.<init>(dataRepositories.kt:10)
at com.example.week3.viewmodel.MovieViewModel.<init>(MovieViewModel.kt:14)
at java.lang.reflect.Constructor.newInstance0(Native Method)
at java.lang.reflect.Constructor.newInstance(Constructor.java:343)
at androidx.lifecycle.ViewModelProvider$AndroidViewModelFactory.create(ViewModelProvider.java:267)
at androidx.lifecycle.SavedStateViewModelFactory.create(SavedStateViewModelFactory.java:106)
at androidx.lifecycle.ViewModelProvider.get(ViewModelProvider.java:185)
at androidx.lifecycle.ViewModelProvider.get(ViewModelProvider.java:150)
at com.example.week3.view.NowPlayingFragment.setContent(NowPlayingFragment.kt:45)
at com.example.week3.view.NowPlayingFragment.onActivityCreated(NowPlayingFragment.kt:40)
at androidx.fragment.app.Fragment.performActivityCreated(Fragment.java:2717)
at androidx.fragment.app.FragmentStateManager.activityCreated(FragmentStateManager.java:336)
at androidx.fragment.app.FragmentManager.moveToState(FragmentManager.java:1186)
at androidx.fragment.app.FragmentManager.moveToState(FragmentManager.java:1354)
at androidx.fragment.app.FragmentManager.moveFragmentToExpectedState(FragmentManager.java:1432)
at androidx.fragment.app.FragmentManager.moveToState(FragmentManager.java:1495)
at androidx.fragment.app.BackStackRecord.executeOps(BackStackRecord.java:447)
at androidx.fragment.app.FragmentManager.executeOps(FragmentManager.java:2167)
at androidx.fragment.app.FragmentManager.executeOpsTogether(FragmentManager.java:1990)
at androidx.fragment.app.FragmentManager.removeRedundantOperationsAndExecute(FragmentManager.java:1945)
at androidx.fragment.app.FragmentManager.execPendingActions(FragmentManager.java:1847)
at androidx.fragment.app.FragmentManager$4.run(FragmentManager.java:413)
at android.os.Handler.handleCallback(Handler.java:883)
at android.os.Handler.dispatchMessage(Handler.java:100)
at android.os.Looper.loop(Looper.java:237)
at android.app.ActivityThread.main(ActivityThread.java:7860)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1075)
我尝试使用调试点对其进行修复，但无济于事，Room始终返回null。