如何修复我的 savedInstanceState 上的 NullPointerException 以及它发生的原因

Question

im has build this mapping application, before on separated android project and its work. when i try to integrate with another system, the problem is occur, i have copy all code same as previous project is mapping system. the problem is there null on my "savedInstanceState" and how i cant fix it?

this for my mapping system for new project, running on mobile phone android 9. i want integrate with project A("..") and project B("mapping system")before integrate all is totally work.

-error message- on  mapView.onCreate(savedInstanceState);

private MapView mapView;
  Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 
'void com.mapbox.mapboxsdk.maps.MapView.onCreate(android.os.Bundle)' 
on a null object reference


  @Override
  protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

            Mapbox.getInstance(this,   "......");
            setContentView(R.layout.activity_main);
            mapView = findViewById(R.id.mapView);

            mapView.onCreate(savedInstanceState);
            mapView.getMapAsync(this);
    }

   @Override
    public void onSaveInstanceState(Bundle outState, PersistableBundle   outPersistentState) {
        super.onSaveInstanceState(outState, outPersistentState);
        mapView.onSaveInstanceState(outState);
    }

expected result: Map is show

actual result: the app is crash because, there null value on my "mapView.onCreate(savedInstanceState);"

Answer 1

savedInstanceState is null when the activity first starts.

The safest way to call it is to make sure it's not null before using it anywhere.

if(savedInstanceState != null) {
   mapView.onCreate(savedInstanceState);
}