MapView 的 onDestroy() 导致 UninitializedPropertyAccessException

Question

Google Map 的 MapView 组件有一个奇怪的问题，导致运行时异常 UninitializedPropertyAccessException。 除了 MapView 的方法被覆盖的视图之外的所有其他视图中的第二次配置更改（设备旋转）后都会引发异常。因此，在处理 com.google.android.gms.maps.MapView 生命周期的 MyMapViewFragment 中不会引发此错误并且配置更改工作正常。

问题出现在所有其他视图中，当我旋转设备时，调用 MyMapViewFragment.onDestroy() 会破坏 com.google.android.gms.maps.MapView：

override fun onDestroy() {
    super.onDestroy()
    googleMapView.onDestroy()
}

第二次旋转设备会导致 googleMapView.onDestroy() 行出现 UninitializedPropertyAccessException - MapView 未初始化。 MyMapViewFragment的代码：

class MyMapViewFragment : Fragment(), OnMapReadyCallback {

   private lateinit var googleMapView: com.google.android.gms.maps.MapView
   private lateinit var googleMap : GoogleMap

  override fun onCreateView(
    inflater: LayoutInflater, container: ViewGroup?,
    savedInstanceState: Bundle?
  ): View? {
    var view = inflater.inflate(R.layout.fragment_map_view, container, false)
    googleMapView = view.findViewById(R.id.mapView2)
    googleMapView.onCreate(savedInstanceState)
    googleMapView.getMapAsync(this)
    bottomNavigationView = requireActivity().findViewById(R.id.bottomNavigation)
    mountainCustomInfoWindow.visibility = View.INVISIBLE
    bottomNavigationView.visibility = View.VISIBLE
    return view
 }

  override fun onMapReady(map: GoogleMap) {
    googleMap = map
  }
  override fun onPause() {
     super.onPause()
     googleMapView.onPause()
  }
  override fun onResume() {
     super.onResume()
     googleMapView.onResume()
  }
  override fun onDestroy() {
     super.onDestroy()
     googleMapView.onDestroy()
  }
  override fun onLowMemory() {
     super.onLowMemory()
     googleMapView.onLowMemory()
  }
}

堆栈跟踪：

Process: com.hiker, PID: 25388
java.lang.RuntimeException: Unable to destroy activity {com.hiker/com.hiker.presentation.MainActivity}: kotlin.UninitializedPropertyAccessException: lateinit property googleMapView has not been initialized
    at android.app.ActivityThread.performDestroyActivity(ActivityThread.java:4605)
    at android.app.ActivityThread.handleDestroyActivity(ActivityThread.java:4623)
    at android.app.ActivityThread.handleRelaunchActivity(ActivityThread.java:4897)
    at android.app.ActivityThread.-wrap19(Unknown Source:0)
    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1702)
    at android.os.Handler.dispatchMessage(Handler.java:105)
    at android.os.Looper.loop(Looper.java:164)
    at android.app.ActivityThread.main(ActivityThread.java:6944)
    at java.lang.reflect.Method.invoke(Native Method)
    at com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:327)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1374)
 Caused by: kotlin.UninitializedPropertyAccessException: lateinit property googleMapView has not been initialized
    at com.hiker.presentation.map.MapView.onDestroy(MapView.kt:173)
    at androidx.fragment.app.Fragment.performDestroy(Fragment.java:2830)
    at androidx.fragment.app.FragmentManagerImpl.moveToState(FragmentManagerImpl.java:1028)
    at androidx.fragment.app.FragmentManagerImpl.moveFragmentToExpectedState(FragmentManagerImpl.java:1238)
    at androidx.fragment.app.FragmentManagerImpl.moveToState(FragmentManagerImpl.java:1310)
    at androidx.fragment.app.FragmentManagerImpl.dispatchStateChange(FragmentManagerImpl.java:2659)
    at androidx.fragment.app.FragmentManagerImpl.dispatchDestroy(FragmentManagerImpl.java:2644)
    at androidx.fragment.app.Fragment.performDestroy(Fragment.java:2825)
    at androidx.fragment.app.FragmentManagerImpl.moveToState(FragmentManagerImpl.java:1028)
    at androidx.fragment.app.FragmentManagerImpl.moveFragmentToExpectedState(FragmentManagerImpl.java:1238)
    at androidx.fragment.app.FragmentManagerImpl.moveToState(FragmentManagerImpl.java:1303)
    at androidx.fragment.app.FragmentManagerImpl.dispatchStateChange(FragmentManagerImpl.java:2659)
    at androidx.fragment.app.FragmentManagerImpl.dispatchDestroy(FragmentManagerImpl.java:2644)
    at androidx.fragment.app.FragmentController.dispatchDestroy(FragmentController.java:329)
    at androidx.fragment.app.FragmentActivity.onDestroy(FragmentActivity.java:366)
    at androidx.appcompat.app.AppCompatActivity.onDestroy(AppCompatActivity.java:210)
    at android.app.Activity.performDestroy(Activity.java:7479)
    at android.app.Instrumentation.callActivityOnDestroy(Instrumentation.java:1255)
    at android.app.ActivityThread.performDestroyActivity(ActivityThread.java:4592)

Answer 1

更多猜测： lateinit 的属性期望在对其进行任何其他操作之前初始化该属性。我们在这种情况下使用它，因为我们只能在 onCreateView 中初始化它，而不是在构造函数中。您确实在onCreateView 的第二行初始化googleMapView。

但是，如果view.findViewById(R.id.mapView2) 将返回null，您实际上可能没有正确初始化它。如果布局fragment_map_view 中没有id 为mapView2 的元素，情况就是这样。所以验证那里确实有一个 MapView。

---

另一种可能发生的情况是，如果 Fragment 实际上并未附加到 View Hierarchy，而是在 Activity 中实例化并注册。当 Activity 被销毁时，它会销毁 Fragment 并在未初始化的对象上调用一个方法。 这里的实际情况

（请参阅 cmets 了解分辨率）。