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ClassCastException occurs when calling another fragment's method

**Re-attached the relevant code
When I run the email app in FragmentB, the activity's 'onStop' is called.
At this time, FragmentA's method in 'onStop' does not work.
※ FragmentA and FragmentB have the same parent Activity
※ No error occurs when the app is terminated in FragmentB.
MainActivity.java
public class MainActivity extends FragmentActivity {
public Fragment fragmentA, fragmentB;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
if (findViewById(R.id.fragment_container) != null) {
if (savedInstanceState != null) {
return;
}
fragmentA = new FragmentA();
fragmentB = new FragmentB();
fragmentA.setArguments(getIntent().getExtras());
getSupportFragmentManager().beginTransaction().add(R.id.fragment_container, fragmentA).commit();
}
}
#Override
protected void onStop() {
super.onStop();
((FragmentA) getSupportFragmentManager().findFragmentById(R.id.fragment_container)).saveData();
}
}
FragmentA.java
View view;
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
view = inflater.inflate(R.layout.fragment_timer, container, false);
if(isLoadData){ loadData(); }
return view;
}
public void saveData() {
SharedPreferences timerSharedPref = getActivity().getSharedPreferences("timer", Context.MODE_PRIVATE);
//...
SharedPreferences.Editor editor = timerSharedPref.edit();
String json = jsonArray.toString();
editor.putString("jsonString", json);
editor.apply();
}
FragmentB.java
public class FragmentB extends Fragment implements View.OnClickListener {
View view;
CardView cvContactUs;
MainActivity activity;
#Override
public void onAttach(#NonNull Context context) {
super.onAttach(context);
activity = (MainActivity) getActivity();
}
#Override
public void onDetach() {
super.onDetach();
activity = null;
}
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
view = inflater.inflate(R.layout.fragment_b, container, false);
cvContactUs = view.findViewById(R.id.cv_contact_us);
return view;
}
#Override
public void onStart() {
super.onStart();
cvContactUs.setOnClickListener(this);
}
#Override
public void onClick(View v) {
int id = v.getId();
if (id == R.id.cv_contact_us) {
sendEmail(getActivity(), "Ask a question", new String[]{"help_center#gmail.com"});
}
}
public static void sendEmail(Context context, String title, String[] receivers){
Intent email = new Intent(Intent.ACTION_SEND);
email.putExtra(Intent.EXTRA_SUBJECT, title);
email.putExtra(Intent.EXTRA_EMAIL, receivers);
email.setType("message/rfc822");
context.startActivity(email);
}
}

You say you are getting a ClassCastException. The only class cast from the code you posted is
(FragmentA) getSupportFragmentManager().findFragmentById(...)
So check whether findFragmentById might return FragmentB or something else. Maybe you want to
either cast to the common parent activity
check whether the returned value is an instance of FragmentA before casting

You have two Fragments in the stack and a single ID and the findFragmentByID() method returns the last fragment added to the container. very well when the application ends with the FragmentA I believe that you don't have any error because in the onStop() method you are casting with the FragmentA, but if you end with the FragmentB in this case you are casting the FragmentB by the FragmentA which throws the ClassCastException exception. so I suggest you use the findFragmentByTag() method here is an example
When you add fragments:
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
/*
* rest of your code
*/
// when you add the Fragment A
getSupportFragmentManager()
.beginTransaction()
.add(R.id.fragment_container, new FragmentA(), "A")
.commit();
// when you add the Fragment A
getSupportFragmentManager()
.beginTransaction()
.add(R.id.fragment_container, new FragmentB(), "B")
.commit();
}
and when you call the onStop() methode:
#Override
protected void onStop() {
super.onStop();
// ((FragmentA) getSupportFragmentManager().findFragmentByTag("A")).save();
// ((FragmentB) getSupportFragmentManager().findFragmentByTag("B")).save();
Fragment f = getSupportFragmentManager().findFragmentByTag("A");
// you check if the fragment is add
if (f != null)
((FragmentA) f).save();
}

Android App crushes when airplane mode is turned off

I am building an application in which I have a Google Maps Fragment. In my MainActivity onCreate() method, I display this Google Maps Fragment which works fine in all cases except with airplane mode. If I turn airplane mode off while the application is running, my app crushes. I tried to include some Logs to see which methods are called and apparently, the following methods are called in order:
onPause() in MapFragment
onPause() in MainActivity
onCreate() in MainActivity
onResume() in MainActivity
and finally the app crushes in onMapReady(GoogleMap googleMap) in the MapFragment when I call
MapsInitializer.initialize(getActivity());
What I do not understand is how and why these methods are called when airplane mode is turned off and how to prevent the application from crushing.
Here is the stack trace of the error
2020-12-03 05:32:44.070 700-700/com.example.mutapamaps E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.mutapamaps, PID: 700
java.lang.NullPointerException: Context is null
at com.google.android.gms.common.internal.Preconditions.checkNotNull(com.google.android.gms:play-services-basement##17.3.0:11)
at com.google.android.gms.maps.MapsInitializer.initialize(Unknown Source)
at com.example.mutapamaps.Fragments.MapFragment.onMapReady(MapFragment.java:218)
at com.google.android.gms.maps.zzac.zza(Unknown Source)
at com.google.android.gms.maps.internal.zzaq.dispatchTransaction(Unknown Source)
at com.google.android.gms.internal.maps.zzb.onTransact(Unknown Source)
at android.os.Binder.transact(Binder.java:504)
at dt.aZ(:com.google.android.gms.dynamite_mapsdynamite#204516046#20.45.16 (040306-0):2)
at com.google.maps.api.android.lib6.impl.bi.run(:com.google.android.gms.dynamite_mapsdynamite#204516046#20.45.16 (040306-0):1)
at android.os.Handler.handleCallback(Handler.java:836)
at android.os.Handler.dispatchMessage(Handler.java:103)
at android.os.Looper.loop(Looper.java:203)
at android.app.ActivityThread.main(ActivityThread.java:6251)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1063)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:924)
Here is my MainActivity
public class MainActivity extends AppCompatActivity{
public static FragmentManager fragmentManager;
public static final String LOG_TAG = "LOG_TAG";
#Override
protected void onCreate(Bundle savedInstanceState) {
Log.i(LOG_TAG, "Main activity created");
super.onCreate(savedInstanceState);
// init airplane mode receiver
IntentFilter intentFilter = new IntentFilter(Intent.ACTION_AIRPLANE_MODE_CHANGED);
BroadcastReceiver receiver = new BroadcastReceiver() {
#Override
public void onReceive(Context context, Intent intent) {
boolean isAirplaneModeOn = intent.getBooleanExtra("state", false);
if(isAirplaneModeOn){
Log.i(LOG_TAG, "Airplane mode turned on");// handle Airplane Mode on
} else {
Log.i(LOG_TAG, "Airplane mode turned off");
}
}
};
this.registerReceiver(receiver, intentFilter);
setContentView(R.layout.activity_main);
fragmentManager = getSupportFragmentManager();
displayFragment(new MapFragment());
}
#Override
protected void onPause() {
super.onPause();
Log.i(LOG_TAG, "Main activity paused");
}
#Override
protected void onResume() {
super.onResume();
Log.i(LOG_TAG, "Main activity resumed");
}
public void displayFragment(Fragment fragmentActivity){
// start the transaction
FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();
fragmentTransaction.replace(R.id.fragment_container, fragmentActivity).
addToBackStack(fragmentActivity.getClass().getSimpleName()).commit();
}
}
Here is my MapFragment
public class MapsFragment extends Fragment implements
OnMapReadyCallback {
public MapsFragment() {
// Required empty public constructor
super();
}
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
// Inflate the layout for this fragment
return inflater.inflate(R.layout.fragment_map, container, false);
}
#Override
public void onViewCreated(#NonNull View view, #Nullable Bundle savedInstanceState) {
FrameLayout map_frame = view.findViewById(R.id.map_frame);
// configure map
MapView mapFragment = view.findViewById(R.id.map_view);
mapFragment.onCreate(savedInstanceState);
mapFragment.onResume();
mapFragment.getMapAsync(this);
View mapView = mapFragment.getRootView();
super.onViewCreated(view, savedInstanceState);
}
#Override
public void onResume() {
super.onResume();
Log.i(LOG_TAG, "MapFragment resumed");
}
#Override
public void onPause() {
super.onPause();
Log.i(LOG_TAG, "Map fragment paused");
}
#Override
public void onMapReady(GoogleMap googleMap) {
Log.i(LOG_TAG, "onMapReadyCalled");
MapsInitializer.initialize(getActivity());
}
}
May you please help me understand what is going on and debug this piece of code.
Thank you in advance.

Change the onViewCreated with this part of code. Hope it helps.
#Override
public void onViewCreated(#NonNull View view, #Nullable Bundle savedInstanceState) {
FrameLayout map_frame = view.findViewById(R.id.map_frame);
// configure map
MapView mapFragment = view.findViewById(R.id.map_view);
mapFragment.onCreate(savedInstanceState);
mapFragment.onResume();
mapFragment.getMapAsync(this);
View mapView = mapFragment.getRootView();
super.onViewCreated(mapView , savedInstanceState);
}

Replace Your MapsFragment with this.
public class MapsFragment extends Fragment implements
OnMapReadyCallback {
Context context;
public MapsFragment() {
// Required empty public constructor
super();
}
#Override
public void onAttach(Context context) {
super.onAttach(context);
this.context = context;
}
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
// Inflate the layout for this fragment
return inflater.inflate(R.layout.fragment_map, container, false);
}
#Override
public void onViewCreated(#NonNull View view, #Nullable Bundle savedInstanceState) {
FrameLayout map_frame = view.findViewById(R.id.map_frame);
// configure map
MapView mapFragment = view.findViewById(R.id.map_view);
mapFragment.onCreate(savedInstanceState);
mapFragment.onResume();
mapFragment.getMapAsync(this);
View mapView = mapFragment.getRootView();
super.onViewCreated(view, savedInstanceState);
}
#Override
public void onResume() {
super.onResume();
Log.i(LOG_TAG, "MapFragment resumed");
}
#Override
public void onPause() {
super.onPause();
Log.i(LOG_TAG, "Map fragment paused");
}
#Override
public void onMapReady(GoogleMap googleMap) {
Log.i(LOG_TAG, "onMapReadyCalled");
MapsInitializer.initialize(context);
}
}

Context is null at onMapReady callback

I'm writing an Android App.
In my App I'm calling a map fragment right after an ACTION_IMAGE_CAPTURE intent is dispatched in the MainActivity.
The map fragment snippet is:
public class MapFragment extends Fragment implements OnMapReadyCallback {
.
.
.
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
// Inflate the layout for this fragment
mView = inflater.inflate(R.layout.fragment_map, container, false);
return mView;
}
#Override
public void onViewCreated(View view, Bundle savedInstanceState) {
super.onViewCreated(view, savedInstanceState);
mMapView = mView.findViewById(R.id.map);
if (mMapView != null) {
mMapView.onCreate(null);
mMapView.onResume();
mMapView.getMapAsync(this);
}
}
.
.
.
#Override
public void onMapReady(GoogleMap googleMap) {
MapsInitializer.initialize(getActivity());
mMap = googleMap;
mMap.setMapType(GoogleMap.MAP_TYPE_NORMAL);
}
If I don't dispatch the ACTION_IMAGE_CAPTURE intent the fragment works as planned, however, when dispatching the intent the context in MapsInitializer.initialize(getActivity()) is null
I think I need to better sync the the ACTION_IMAGE_CAPTURE intent completion and the onMapReady method but not sure how.
Any help will be appreciated.
Thanks,

Change to this,
#Override
public void onViewCreated(View view, Bundle savedInstanceState) {
super.onViewCreated(view, savedInstanceState);
mMapView = mView.findViewById(R.id.map);
//initialize before calling map onCreate
MapsInitializer.initialize(getActivity());
if (mMapView != null) {
//instead of passing null its a good practice to use savedInstanceState
mMapView.onCreate(savedInstanceState);
mMapView.onResume();
mMapView.getMapAsync(this);
}
}

Map fragment lag on scroll

I am using a Google Maps fragment with a MapView that starts by getting user location and setting a marker with it. But i noticed a lag when user scrolls the map, it's like a frame drop.
I searched for some reasons, but i guess it depends on my code. Something seems wrong, but i don't know what yet.
Here's the code:
MainActivity.java
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
setFragment(new MapFragment());
}
protected void setFragment(Fragment fragment) {
FragmentManager fragmentManager = getSupportFragmentManager();
android.support.v4.app.FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();
fragmentTransaction.replace(android.R.id.content, fragment);
fragmentTransaction.commit();
}
MapFragment.java
GoogleMap mGoogleMap;
MapView mMapView;
View mView;
LocationManager mLocationManager;
Location mUserLocation;
private final String TAG_PARSING_STYLE_FAILURE = "ERROR PARSING JSON";
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
mLocationManager = (LocationManager) getContext().getSystemService(Context.LOCATION_SERVICE);
}
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
// Inflate the layout for this fragment
mView = inflater.inflate(R.layout.fragment_map, container, false);
return mView;
}
#Override
public void onViewCreated(View view, #Nullable Bundle savedInstanceState) {
super.onViewCreated(view, savedInstanceState);
mMapView = (MapView) mView.findViewById(R.id.testMapView);
if( mMapView != null){
mMapView.onCreate(null);
mMapView.onResume();
mMapView.getMapAsync(this);
}
}
#Override
public void onMapReady(GoogleMap googleMap) {
MapsInitializer.initialize(getContext());
mGoogleMap = googleMap;
mGoogleMap.setMapType(GoogleMap.MAP_TYPE_NORMAL);
mUserLocation = getUserLocation();
LatLng latLng = new LatLng(mUserLocation.getLatitude(), mUserLocation.getLongitude());
MarkerOptions marker = new MarkerOptions();
marker.position(latLng);
marker.title("My Location");
mGoogleMap.addMarker(marker);
CameraPosition cameraPosition = CameraPosition.builder().target(latLng).zoom(17).build();
mGoogleMap.moveCamera(CameraUpdateFactory.newCameraPosition(cameraPosition));
}
public Location getUserLocation(){
Location loc = null;
try {
loc = mLocationManager.getLastKnownLocation(LocationManager.GPS_PROVIDER);
} catch (SecurityException ex) {
Log.e("ERROR - LOCATION", ex.toString());
}
return loc;
}
Is there a better approach when using MapFragments?

Android crashes on calling FragmentTransaction Replace method?

What I am trying to do is to use only one Activity as a host for many fragments such as the activity will host only one fragment at a time and the fragments should attached to the activity in a certain order.
My Fragment code:
public class FirstFragment extends Fragment{
//some code here to instantiate FirstFragment here.
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.main, container, false);
Button button = (Button) view.findViewById(R.id.button1);
button.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
((MainActivity) getActivity()).onFirstFragmentFinished(position);
}
});
return view;
}
// Container Activity must implement this interface
public interface FirstFragmentListener {
public void onFirstFragmentFinished(int position);
}
}
Simply, in each fragment I have a button when pressed it will get the host activity and call the implemented method of FirstFragmentListener interface.
public class MainActivity extends AppCompatActivity implements FirstFragmentListener {
#Override
public void onCreateView(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
FragmentManager fragmentManager = getSupportFragmentManager();
FragmentTransaction fragmentTra = fragmentManager.beginTransaction();
fragmentTra .replace(R.id.main_layout, new FirstFragment());
fragmentTra.commit();
}
#Override
public void onFirstFragmentFinished(int position)
{
if(position == 1)
{
FragmentManager fragmentManager = getSupportFragmentManager();
FragmentTransaction fragmentTra = fragmentManager.beginTransaction();
fragmentTra .replace(R.id.main_layout, new SecondFragment());
fragmentTra.commit();
}
}
}
When the activity is created, always replace whatever inside this activity with FirstFragment layout.
When the FirstFragment finishes its work and the button on that fragment is pressed, it will call the implemented method of FirstFragment interface on this activity and then check the position for some value, if the condition is correct then go and replace FirstFragment with The SecondFragment instance.
The app is crashing when commit() method is called.

Use of your onFirstFragmentFinished is wrong. Look at official doc:
android-comunication-activity-ffragment
It is prefer to Override onAttach() method.

In Fragment you need View to bind with fragment like this :
public class FirstFragment extends Fragment {
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.main, container, false);
Button button = (Button) view.findViewById(R.id.button1);
button.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
if(position == 1){
SecondFragment secondFrag= new SecondFragment();
getActivity().getFragmentManager().beginTransaction()
.replace(R.id.main_layout, secondFrag)
.addToBackStack(null)
.commit();
}
}
});
return view;
}
}

I look at my stack trace and I found this exception:
com.example.exchange.msbexchange E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.exchange.msbexchange, PID: 17975
java.lang.RuntimeException: com.example.exchange.msbexchange.MainActivity#1e7d93b must implement OnFragmentInteractionListener
at com.example.exchange.msbexchange.CurrencyFragment.onAttach(CurrencyFragment.java:83)
at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1030)
at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1259)
at android.support.v4.app.BackStackRecord.run(BackStackRecord.java:738)
at android.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1624)
at android.support.v4.app.FragmentManagerImpl$1.run(FragmentManager.java:517)
at android.os.Handler.handleCallback(Handler.java:739)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:145)
at android.app.ActivityThread.main(ActivityThread.java:6117)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1399)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1194)
It is obviousely because my MainActivity does not implement the interface of the SecondFragment Class. I did not know this is mandatory for the fragments to work. I just need to implement the interface and now it is working.

you need implement your interface FirstFragmentListener in onAttach in fragment
FirstFragmentListener mCallback;
#Override
public void onAttach(Activity activity) {
super.onAttach(activity);
// This makes sure that the container activity has implemented
// the callback interface. If not, it throws an exception
try {
mCallback = (FirstFragmentListener) activity;
} catch (ClassCastException e) {
throw new ClassCastException(activity.toString()
+ " must implement OnHeadlineSelectedListener");
}
}
then use it as you do on click or what ever you want

Where do you get position variable from? It seems that this variable does not have value...
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.main, container, false);
Button button = (Button) view.findViewById(R.id.button1);
button.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
((MainActivity) getActivity()).onFirstFragmentFinished(position);
}
});
return view;
}