在活动的onCreate之前调用片段的onCreateView

Question

I have my VehicleListActivity which passes a Bundle to my fragment. This is activity's onCreate method:

@Override
protected void onCreate(Bundle savedInstanceState)
{
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_vehicle_list);
    vehicles = new ArrayList<>();

    Intent intent = getIntent();
    String userID = intent.getStringExtra("userID");
    LoadingVehicleListFragment f = new LoadingVehicleListFragment();
    Bundle fArguments = new Bundle();
    fArguments.putString("userID", userID);
    f.setArguments(fArguments);
    getSupportFragmentManager().beginTransaction().add(R.id.loadingVehicleFragment, f).commit();
}

and this is fragment's onCreateView :

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState)
{
    activity = (VehicleListActivity)getActivity();
    context = activity;
    listener = activity;
    String userID = getArguments().getString("userID");
    getUserInformation(userID);

    return inflater.inflate(com.devspark.progressfragment.R.layout.fragment_progress, container, false);
}

I've noticed that fragment's onCreateView is called before activity's onCreate , so getArguments() in my fragment returns a null, which causes a null pointer exception. Where should I put getArguments() in my fragment to avoid this exception?

EDIT: as requested this is the whole fragment's source:

public class LoadingVehicleListFragment extends ProgressFragment
{
private VehicleListListener listener;
private VehicleListActivity activity;

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState)
{
    return inflater.inflate(com.devspark.progressfragment.R.layout.fragment_progress, container, false);
}

/*@Override
public void onActivityCreated(@Nullable Bundle savedInstanceState)
{
    super.onActivityCreated(savedInstanceState);
    int c = 0;
    listener = (VehicleListActivity)getActivity();
    getUserInformation(getArguments().getString("userID"));
}*/

private void getUserVehicles(String userID)
{
    Response.Listener<String> responseListener = new Response.Listener<String>()
    {
        @Override
        public void onResponse(String response)
        {
            try
            {
                HashMap resultMap = new ObjectMapper().readValue(response, HashMap.class);
                VehicleListRequest.ErrorCode errorCode = VehicleListRequest.ErrorCode.fromInt(Integer.parseInt(resultMap.get("error_code").toString()));

                switch (errorCode)
                {
                    case NONE:
                        parseVehicleFromMap(resultMap);
                        break;
                    case EXCEPTION_CAUGHT:
                        AlertDialog.Builder builder2 = new AlertDialog.Builder(getActivity());
                        builder2.setMessage("Eccezione catturata. \n Messaggio: " + resultMap.get("error_message"));
                        builder2.create().show();
                        break;
                }
            }
            catch (IOException e)
            {
                // TODO gestire
                e.printStackTrace();
            }
        }
    };

    VehicleListRequest request = new VehicleListRequest(userID, responseListener, null);
    RequestQueue requestQueue = Volley.newRequestQueue(getActivity());
    requestQueue.add(request);
}

public void getUserInformation(final String userID)
{
    Response.Listener<String> responseListener = new Response.Listener<String>()
    {
        @Override
        public void onResponse(String response)
        {
            try
            {
                HashMap resultMap = new ObjectMapper().readValue(response, HashMap.class);
                GetUserRequest.ErrorCode errorCode = GetUserRequest.ErrorCode.fromInt(Integer.parseInt(resultMap.get("error_code").toString()));

                switch (errorCode)
                {
                    case NONE:
                        listener.setLoggedUser(User.fromMap(resultMap));
                        getUserVehicles(userID);
                        break;
                    case EXCEPTION_CAUGHT:
                        AlertDialog.Builder builder2 = new AlertDialog.Builder(getActivity());
                        builder2.setMessage("Eccezione catturata. \n Messaggio: " + resultMap.get("error_message"));
                        builder2.create().show();
                        break;
                }
            }
            catch (IOException e)
            {
                // TODO gestire
                e.printStackTrace();
            }
        }
    };

    GetUserRequest request = new GetUserRequest(userID, responseListener, null);
    RequestQueue requestQueue = Volley.newRequestQueue(getActivity());
    requestQueue.add(request);
}

private void parseVehicleFromMap(HashMap map)
{
    int i = 0;

    while (map.containsKey(String.valueOf(i)))
    {
        final Vehicle v = new Vehicle();
        HashMap vehicleMap = (HashMap) map.get(String.valueOf(i));

        v.setPlate(vehicleMap.get("plate").toString());
        v.setKm(vehicleMap.get("km") == null ? null : Integer.parseInt(vehicleMap.get("km").toString()));
        v.setInUse(Integer.parseInt(vehicleMap.get("in_use").toString()) == 1);
        v.setFuelQuantity(Double.parseDouble(vehicleMap.get("actual_fuel_quantity").toString()));
        v.setEffectiveFuelEconomy(Double.parseDouble(vehicleMap.get("effective_fuel_economy").toString()));
        v.setInsuranceDate(vehicleMap.get("insurance_date") == null ? null : new LocalDate(vehicleMap.get("insurance_date").toString()));
        v.setMatriculationDate(new LocalDate(vehicleMap.get("matriculation_date").toString()));
        v.setLatitude(vehicleMap.get("latitude") == null ? null : Double.parseDouble(vehicleMap.get("latitude").toString()));
        v.setLongitude(vehicleMap.get("longitude") == null ? null : Double.parseDouble(vehicleMap.get("longitude").toString()));
        v.setUser(activity.getLogged());

        listener.addVehicle(v);

        i++;
    }
}
} // end class

this is error logs:

03-27 18:30:47.274 4966-4966/clyky.cartracker E/AndroidRuntime: FATAL EXCEPTION: main
                                                            Process: clyky.cartracker, PID: 4966
                                                            java.lang.RuntimeException: Unable to start activity ComponentInfo{clyky.cartracker/clyky.cartracker.activities.VehicleListActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String android.os.Bundle.getString(java.lang.String)' on a null object reference
                                                                at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2434)
                                                                at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2504)
                                                                at android.app.ActivityThread.-wrap11(ActivityThread.java)
                                                                at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1347)
                                                                at android.os.Handler.dispatchMessage(Handler.java:102)
                                                                at android.os.Looper.loop(Looper.java:148)
                                                                at android.app.ActivityThread.main(ActivityThread.java:5458)
                                                                at java.lang.reflect.Method.invoke(Native Method)
                                                                at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
                                                                at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
                                                             Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String android.os.Bundle.getString(java.lang.String)' on a null object reference
                                                                at clyky.cartracker.activities.fragments.LoadingVehicleListFragment.onActivityCreated(LoadingVehicleListFragment.java:51)
                                                                at android.support.v4.app.Fragment.performActivityCreated(Fragment.java:2193)
                                                                at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1323)
                                                                at android.support.v4.app.FragmentManagerImpl.moveFragmentToExpectedState(FragmentManager.java:1523)
                                                                at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1585)
                                                                at android.support.v4.app.FragmentManagerImpl.dispatchActivityCreated(FragmentManager.java:2832)
                                                                at android.support.v4.app.FragmentController.dispatchActivityCreated(FragmentController.java:201)
                                                                at android.support.v4.app.FragmentActivity.onStart(FragmentActivity.java:603)
                                                                at android.support.v7.app.AppCompatActivity.onStart(AppCompatActivity.java:181)
                                                                at android.app.Instrumentation.callActivityOnStart(Instrumentation.java:1237)
                                                                at android.app.Activity.performStart(Activity.java:6268)
                                                                at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2397)
                                                                at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2504) 
                                                                at android.app.ActivityThread.-wrap11(ActivityThread.java) 
                                                                at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1347) 
                                                                at android.os.Handler.dispatchMessage(Handler.java:102) 
                                                                at android.os.Looper.loop(Looper.java:148) 
                                                                at android.app.ActivityThread.main(ActivityThread.java:5458) 
                                                                at java.lang.reflect.Method.invoke(Native Method) 
                                                                at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726) 
                                                                at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616) 

before of these exceptions, I've also got some "failed binder transactions", like these:

03-27 18:30:41.955 1452-1452/com.google.android.inputmethod.latin E/JavaBinder: !!! FAILED BINDER TRANSACTION !!!  (parcel size = 100)

03-27 18:30:41.956 1452-1452/com.google.android.inputmethod.latin E/AndroidIME: aqx: java.lang.RuntimeException: android.os.DeadObjectException: Transaction failed on small parcel; remote process probably died 03-27 18:30:41.999 1452-1452/com.google.android.inputmethod.latin E/JavaBinder: !!! FAILED BINDER TRANSACTION !!! (parcel size = 100) 03-27 18:30:42.000 1452-1452/com.google.android.inputmethod.latin E/AndroidIME: aqx: java.lang.RuntimeException: android.os.DeadObjectException: Transaction failed on small parcel; remote process probably died 03-27 18:30:42.001 1452-1452/com.google.android.inputmethod.latin E/JavaBinder: !!! FAILED BINDER TRANSACTION !!! (parcel size = 100) 03-27 18:30:42.002 1452-1452/com.google.android.inputmethod.latin E/AndroidIME: aqx: java.lang.RuntimeException: android.os.DeadObjectException: Transaction failed on small parcel; remote process probably died 03-27 18:30:42.005 1452-1452/com.google.android.inputmethod.latin E/JavaBinder: !!! FAILED BINDER TRANSACTION !!! (parcel size = 100) 03-27 18:30:42.007 1452-1452/com.google.android.inputmethod.latin E/AndroidIME: aqx: java.lang.RuntimeException: android.os.DeadObjectException: Transaction failed on small parcel; remote process probably died 03-27 18:30:42.008 1452-1452/com.google.android.inputmethod.latin E/JavaBinder: !!! FAILED BINDER TRANSACTION !!! (parcel size = 100) 03-27 18:30:42.010 1452-1452/com.google.android.inputmethod.latin E/AndroidIME: aqx: java.lang.RuntimeException: android.os.DeadObjectException: Transaction failed on small parcel; remote process probably died 03-27 18:30:42.026 1452-5094/com.google.android.inputmethod.latin E/JavaBinder: !!! FAILED BINDER TRANSACTION !!! (parcel size = 168) 03-27 18:30:42.031 1452-5095/com.google.android.inputmethod.latin E/JavaBinder: !!! FAILED BINDER TRANSACTION !!! (parcel size = 168) 03-27 18:30:43.509 1452-1452/com.google.android.inputmethod.latin E/JavaBinder: !!! FAILED BINDER TRANSACTION !!! (parcel size = 100) 03-27 18:30:43.510 1452-1452/com.google.android.inputmethod.latin E/AndroidIME: aqx: java.lang.RuntimeException: android.os.DeadObjectException: Transaction failed on small parcel; remote process probably died 03-27 18:30:43.510 1452-1452/com.google.android.inputmethod.latin E/JavaBinder: !!! FAILED BINDER TRANSACTION !!! (parcel size = 100) 03-27 18:30:43.512 1452-1452/com.google.android.inputmethod.latin E/AndroidIME: aqx: java.lang.RuntimeException: android.os.DeadObjectException: Transaction failed on small parcel; remote process probably died 03-27 18:30:43.542 1452-5121/com.google.android.inputmethod.latin E/JavaBinder: !!! FAILED BINDER TRANSACTION !!! (parcel size = 168) 03-27 18:30:43.547 1452-5120/com.google.android.inputmethod.latin E/JavaBinder: !!! FAILED BINDER TRANSACTION !!! (parcel size = 168)

however, they starts to appear before the operations that throw exception, so I think that these errors aren't influential.

Answer 1

The onActivityCreated() is called after the onCreateView() method when the host activity is created. Activity and fragment instance have been created as well as the view hierarchy of the activity. At this point, view can be accessed with the findViewById() method. example. In this method you can instantiate objects which require a Context object.

Try accessing it there, also do not store context in fragments always call getActivity()

That Null Pointer is caused by the flow of execution in the android framework, onCreateView() The system calls this callback when it's time for the fragment to draw its user interface for the first time. To draw a UI for your fragment, you must return a View component from this method that is the root of your fragment's layout. You can return null if the fragment does not provide a UI. Therefore it is called first, hence giving the null pointer exception.

Answer 2

Can you try this?

@Override
protected void onCreate(Bundle savedInstanceState)
{
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_vehicle_list);
    vehicles = new ArrayList<>();

    String userID;
    Bunlde bundle = getIntent().getExtras();
    if(bundle != null){
        userID = bundle.getString("userID");
    }

    if(savedInstanceState == null){
          LoadingVehicleListFragment f = new LoadingVehicleListFragment();
          Bundle fArguments = new Bundle();
          fArguments.putString("userID", userID);
          f.setArguments(fArguments);
          getSupportFragmentManager().beginTransaction().replace(R.id.loadingVehicleFragment, f).commit();
    }
}