FragmentActivity总是重新创建，savedInstanceState始终为null

Question

我已使用Android Studio向导创建带有Google地图的APP。 在我的应用程序的主要活动有一个地图，我可以添加一些标记。此外，还有一个菜单可以调用其他3个活动。

当用户打开辅助活动然后关闭它（例如按下后退按钮或单击按钮以调用完成）时，辅助活动已关闭，但主活动始终是重新创建（onCreate方法是调用）和地图重新创建，所以我丢失了标记和相机选项。

我尝试使用onSaveInstanceState来保存标记和相机设置，但我无法恢复它，因为onCreate的savedInstanceState参数始终为null。 我也尝试使用onRestoreInstanceState，但是这个方法永远不会调用，除了我测试onSaveInstanceState，当我尝试打开辅助活动时，这总是调用。

我怎样才能避免每次都重新创建地图？ savedInstanceState的问题在哪里？

这是我的应用程序代码（主要活动）的摘录：

public class MapsActivity extends FragmentActivity implements GoogleMap.OnInfoWindowClickListener, GoogleMap.OnMarkerClickListener, GoogleMap.OnMapClickListener, GoogleMap.OnMapLongClickListener, GoogleMap.OnCameraChangeListener {
...

List<MapPoint> MapPointsList = new ArrayList<MapPoint>();


@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_maps);
    setUpMapIfNeeded();

    if (savedInstanceState !=  null) {
        mCurrentMapCenterLatitude = savedInstanceState.getDouble("mCurrentMapCenterLatitude");
        mCurrentMapCenterLongitude = savedInstanceState.getDouble("mCurrentMapCenterLongitude");
        mCurrentMapZoom = savedInstanceState.getFloat("mCurrentMapZoom");

        MapPointsList.clear();
        MapPolylinesList.clear();

        ArrayList<MapPointsParcelable> list;
        list = savedInstanceState.getParcelableArrayList("MapPointsList");

        for (MapPointsParcelable aList : list) {
            MapPoint mapPoint = new MapPoint(aList.name, aList.latitude, aList.longitude, aList.status, aList.kind);
            mapPoint.selected = aList.selected;
            MapPointsList.add(mapPoint);
        }

        mapRestore = true;
    }
}

@Override
protected void onResume() {
    super.onResume();
    setUpMap();
}

@Override
public void onSaveInstanceState(Bundle savedInstanceState) {
    super.onSaveInstanceState(savedInstanceState);
    savedInstanceState.putDouble("mCurrentMapCenterLatitude", mCurrentMapCenterLatitude);
    savedInstanceState.putDouble("mCurrentMapCenterLongitude", mCurrentMapCenterLongitude);
    savedInstanceState.putFloat("mCurrentMapZoom", mCurrentMapZoom);

    ArrayList<MapPointsParcelable> list;
    list = new ArrayList<MapPointsParcelable>();

    for (MapPoint aMapPointsList : MapPointsList) {
        list.add(new MapPointsParcelable(aMapPointsList.name, aMapPointsList.latitude, aMapPointsList.longitude, aMapPointsList.status, aMapPointsList.kind, aMapPointsList.realname, aMapPointsList.selected));
    }

    savedInstanceState.putParcelableArrayList("MapPointsList", list);
}

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    new MenuInflater(getApplication()).inflate(R.menu.action_bar_menu, menu);
    return super.onCreateOptionsMenu(menu);
}

@Override
public boolean onOptionsItemSelected(MenuItem item) {
    switch (item.getItemId()) {
        case R.id.action_search:
            openSearchActivity();
            return true;
        case R.id.action_settings:
            openSettingsActivity();
            return true;
        case R.id.action_credits:
            openCreditsActivity();
            return true;
        default:
            return super.onOptionsItemSelected(item);
    }
}

@Override
public void onConfigurationChanged(Configuration newConfig) {
    super.onConfigurationChanged(newConfig);
}

private void setUpMapIfNeeded() {
    // Do a null check to confirm that we have not already instantiated the map.
    if (mMap == null) {
        // Try to obtain the map from the SupportMapFragment.
        mMap = ((SupportMapFragment) getSupportFragmentManager().findFragmentById(R.id.map)).getMap();
        // Check if we were successful in obtaining the map.
        if (mMap != null) {
            mMap.setMyLocationEnabled(true);
            setUpMap();
        }
    }

    if (mLocation == null) {
        mLocation = ((LocationManager) getSystemService(LOCATION_SERVICE));
    }
}

private void openSearchActivity() {
    Intent intent = new Intent(this, SearchActivity.class);
    startActivityForResult(intent, 1);
}

private void openSettingsActivity() {
    Intent intent = new Intent(this, SettingsActivity.class);
    startActivityForResult(intent, 2);
}

private void openCreditsActivity() {
    Intent intent = new Intent(this, CreditsActivity.class);
    startActivity(intent);
}

...

}