onCreate() 之前的 Activity 无法使用的系统服务：ROOM

Question

我有这个 activity，当我点击一个图像时我有这个回调。它工作正常，但现在我补充说，如果单击它，它会将数据保存在数据库中。问题是，现在我收到系统服务不可用错误，我不确定如何修复它。有什么想法吗？

这是activity（我只展示了它的相关部分）：

class MainActivity : AppCompatActivity(), RecyclerAdapter.Callback, androidx.appcompat.widget.SearchView.OnQueryTextListener {
   private lateinit var binding: ActivityMainBinding
   private val movies = mutableListOf<Movie>()
   private lateinit var adapter: RecyclerAdapter
   private lateinit var progressBar: ProgressBar
   private lateinit var mMoviesViewModel: MoviesViewModel

   private val viewModel: MainViewModel by viewModels(
       factoryProducer = { MainViewModelFactory() }
   )

   override fun onCreate(savedInstanceState: Bundle?) {
       super.onCreate(savedInstanceState)
       binding = ActivityMainBinding.inflate(layoutInflater)
       setContentView(binding.root)
       binding.svSearch.setOnQueryTextListener(this)
       //setup progress bar
       progressBar = binding.ProgressBar
       progressBar.visibility = View.VISIBLE

       setObservers()
       initRecyclerView()


   }

private fun initRecyclerView() {
       adapter = RecyclerAdapter(movies)
       binding.rvMovies.layoutManager = GridLayoutManager(this, 3)
       binding.rvMovies.adapter = adapter
       adapter.callback = this
   }

//instantiate database for later
   val db = Room.databaseBuilder(
       this,
       MoviesDatabase::class.java, "database-name"
   ).build()

   val dao = db.moviesDao()


   //send details of clicked movie to fragment
   override fun onMovieClicked(movie: Movie) {
       val transaction = supportFragmentManager
       val detailFragment = DetailFragment()
       val data = Bundle()

       //check if movie is already in database

       if(dao.movieExists(movie.id)){
           //send movie's id to fragment
           data.putString("Title", movie.title)
           detailFragment.arguments = data
       } else {

           val title = movie.title
           val image = movie.poster
           val overview = movie.overview
           val language = movie.originalLanguage
           val releaseDate = movie.releaseDate
           val popularity = movie.popularity
           val voteAverage = movie.voteAverage

           //create movie object
           val movie = Movies(id =0, title, image, overview,
               language, popularity, releaseDate, voteAverage
           )

           //add data to db
           mMoviesViewModel.addMovie(movie)

           //send movie's id to fragment
           data.putString("Title", movie.title)
           detailFragment.arguments = data
       }
       //pass data to fragment
       transaction.beginTransaction()
           .replace(R.id.frag_container, detailFragment)
           .addToBackStack(null)
           .commit()
   }

}

堆栈跟踪：

E/AndroidRuntime: FATAL EXCEPTION: main
   Process: com.app.challengemovieapp.develop, PID: 13142
   java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.app.challengemovieapp.develop/com.app.challengemovieapp.ui.MainActivity}: java.lang.IllegalStateException: System services not available to Activities before onCreate()
       at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3032)
       at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3269)
       at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:78)
       at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:108)
       at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:68)
       at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1960)
       at android.os.Handler.dispatchMessage(Handler.java:106)
       at android.os.Looper.loop(Looper.java:214)
       at android.app.ActivityThread.main(ActivityThread.java:7094)
       at java.lang.reflect.Method.invoke(Native Method)
       at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:494)
       at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:975)
    Caused by: java.lang.IllegalStateException: System services not available to Activities before onCreate()
       at android.app.Activity.getSystemService(Activity.java:6143)
       at androidx.room.RoomDatabase$JournalMode.resolve(RoomDatabase.java:663)
       at androidx.room.RoomDatabase$Builder.build(RoomDatabase.java:1346)
       at com.app.challengemovieapp.ui.MainActivity.<init>(MainActivity.kt:129)
       at java.lang.Class.newInstance(Native Method)
       at android.app.AppComponentFactory.instantiateActivity(AppComponentFactory.java:69)
       at androidx.core.app.CoreComponentFactory.instantiateActivity(CoreComponentFactory.java:45)
       at android.app.Instrumentation.newActivity(Instrumentation.java:1219)
       at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3020)
       at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3269) 
       at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:78) 
       at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:108) 
       at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:68) 
       at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1960) 
       at android.os.Handler.dispatchMessage(Handler.java:106) 
       at android.os.Looper.loop(Looper.java:214) 
       at android.app.ActivityThread.main(ActivityThread.java:7094) 
       at java.lang.reflect.Method.invoke(Native Method) 
       at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:494) 
       at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:975) 

Answer 1

您需要移动这些行：

   val db = Room.databaseBuilder(
       this,
       MoviesDatabase::class.java, "database-name"
   ).build()

   val dao = db.moviesDao()

Room 需要调用 Context 上的方法，这些方法在您的 MainActivity 实例化时尚未就绪。在 onCreate() 函数 super.onCreate() 之前，您不应该尝试使用 Room。