I have an android app that consists of a number of nested fragments, for example I have a set of tabs and clicking a tab loads a fragment into the content area.
One of my tabs is a map showing locations on it and I am doing a geo lookup on a postcode to get back the coordinates for it.
This is all working and now finally I need to ensure that if a user clicks the map tab and initiates the async task which does the geo lookup that a device rotation doesnt stop this.
My map fragment which is loaded when the tab is clicked:
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
// Inflate the layout for this fragment
View rootView = (View)inflater.inflate(R.layout.fragment_locations, container, false);
// Make sure user's device supports Google play services
try {
MapsInitializer.initialize(getActivity());
mapView = (MapView) rootView.findViewById(R.id.mapView);
mapView.onCreate(savedInstanceState);
googleMap = mapView.getMap();
Log.i(LOG_TAG, "Google play service is available.");
if(googleMap == null) {
Toast.makeText(getActivity().getApplicationContext(), "Problem creating Google map", Toast.LENGTH_LONG).show();
} else {
googleMap.setMapType(GoogleMap.MAP_TYPE_NORMAL);
googleMap.getUiSettings().setZoomControlsEnabled(true);
FragmentManager fm = getFragmentManager();
mRetainedTaskFragment = (LocationNetworkOperationsRetainedFragment) fm.findFragmentByTag(TAG_RETAINED_TASK_FRAGMENT);
// If the Fragment is non-null, then it is currently being
// retained across a configuration change.
if (mRetainedTaskFragment == null) {
mRetainedTaskFragment = new LocationNetworkOperationsRetainedFragment();
fm.beginTransaction().add(mRetainedTaskFragment, TAG_RETAINED_TASK_FRAGMENT).commit();
}
}
} catch (Exception e) {
Log.e(LOG_TAG, "Google play service is not available.");
Toast.makeText(getActivity().getApplicationContext(), "Google play service is not available", Toast.LENGTH_LONG).show();
}
return rootView;
}
My async task:
public class LocationNetworkOperations extends AsyncTask<String, Void, LatLng> {
@Override
protected LatLng doInBackground(String... postcodes) {
Geocoder geocoder = new Geocoder(getActivity().getApplicationContext());
LatLng coords= null;
try {
List<Address> addresses = geocoder.getFromLocationName(postcodes[0], 1);
if (addresses != null && !addresses.isEmpty()) {
Address address = addresses.get(0);
coords = new LatLng(address.getLatitude(), address.getLongitude());
} else {
Toast.makeText(getActivity().getApplicationContext(), "Unable to geocode postcode" + postcodes[0], Toast.LENGTH_LONG).show();
}
} catch(Exception ioe) {
ioe.printStackTrace();
}
return coords;
}
@Override
protected void onPostExecute(LatLng coords) {
if(coords != null) {
Marker mapMarkerHome = googleMap.addMarker(new MarkerOptions().position(coords).title("Home")
.snippet("E10 6JQ").icon(BitmapDescriptorFactory
.fromResource(R.drawable.home_map_marker)));
CameraPosition cameraPosition = new CameraPosition.Builder().target(coords).zoom(15).build();
googleMap.animateCamera(CameraUpdateFactory.newCameraPosition(cameraPosition));
}
}
@Override
protected void onPreExecute() {}
@Override
protected void onProgressUpdate(Void... values) {}
}
The retained fragment:
public class LocationNetworkOperationsRetainedFragment extends Fragment {
interface LocationNetworkOperationsTaskCallbacks {
void onPreExecute();
void onProgressUpdate(int percent);
void onCancelled();
void onPostExecute();
}
private LocationNetworkOperationsTaskCallbacks mCallbacks;
private LocationsFragment.LocationNetworkOperations mTask;
@Override
public void onAttach(Context context) {
super.onAttach(context);
mCallbacks = (LocationNetworkOperationsTaskCallbacks) context;
}
/**
* This method will only be called once when the retained
* Fragment is first created.
*/
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
// Retain this fragment across configuration changes.
setRetainInstance(true);
// Create and execute the background task.
mTask = new LocationsFragment().new LocationNetworkOperations();
mTask.execute("E106JQ");
}
@Override
public void onDetach() {
super.onDetach();
mCallbacks = null;
}
}
So I followed a tutorial and wrote a retained fragment and kick off the aysnc task in that but I am running into the following exception:
java.lang.IllegalStateException: Can't retain fragements that are nested in other fragments
at android.support.v4.app.Fragment.setRetainInstance(Fragment.java:820)
at com.example.android.LocationNetworkOperationsRetainedFragment.onCreate(LocationNetworkOperationsRetainedFragment.java:37)
at android.support.v4.app.Fragment.performCreate(Fragment.java:1939)
at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:988)
at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1207)
at android.support.v4.app.BackStackRecord.run(BackStackRecord.java:738)
at android.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1572)
at android.support.v4.app.FragmentManagerImpl$1.run(FragmentManager.java:493)
at android.os.Handler.handleCallback(Handler.java:739)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:5417)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
Why is it not possible to retain the fragment if it is nested and is there a solution to this?
