Develop Reference

How to resolve error findViewById error in android fragment

I'm trying to add recyclerview in my fragment but I'm getting error when I click on navigation drawer item.
Attempt to invoke virtual method 'android.view.View android.view.View.findViewById(int)' on a null object reference
at com.example.myapplication.fragment.Books.onCreate(Books.java:45)
How to resolve error or suggest tutorial to load json data in fragment using recyclerview. with click event on recyclerview. on click item open new fragment with data.
This is my code
public class Books extends Fragment {
private BooksModel booksViewModel;
private RecyclerView recyclerView;
private RecyclerView.Adapter adapter;
private List<BooksModel> bookLists;
// Context context;
#Override
public void onCreate(#Nullable Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
recyclerView = (RecyclerView) getView().findViewById(R.id.recyclerViewBook); //Line 45 Error
recyclerView.setHasFixedSize(true);
recyclerView.setLayoutManager(new LinearLayoutManager(getActivity()));
bookLists = new ArrayList<>();
for(int i=0; i<=10; i++){
BooksModel bookList = new BooksModel(
"",
"Title " + (i + 1),
"This is Auther"
);
bookLists.add(bookList);
adapter = new BooksAdapter(bookLists,this);
recyclerView.setAdapter(adapter);
}
}
public View onCreateView(#NonNull LayoutInflater inflater,
ViewGroup container, Bundle savedInstanceState) {
booksViewModel =
new ViewModelProvider(this).get(BooksModel.class);
View root = inflater.inflate(R.layout.fragment_books, container, false);
final TextView textView = root.findViewById(R.id.text_book );
booksViewModel.getText().observe(getViewLifecycleOwner(), new Observer<String>() {
#Override
public void onChanged(#Nullable String s) {
textView.setText(s);
}
});
return root;
}
}

onCreate() runs before onCreateView(). You should move all of that code to onViewCreated(), which passes you the View directly (meaning you don't have to call getView() at all).

RecyclerView Android Studio on the Fragment raises a red line [duplicate]

This question already has answers here:
I get the error "Unreachable statement" return in android
(3 answers)
Closed 3 years ago.
I have this code, which integrates a RecyclerView within a Fragment, but this line:
mRecyclerView = (RecyclerView) mRecyclerView.findViewById(R.id.list_data);
Gives me an error, it tells me that:
Unreachable statement
And I don't know why, any idea?
Here's the code I'm using:
public class KecamatanFragment extends Fragment {
private static final String data_url = "http://xxxxxxxxxx/daftar/get_kecamatan.php"; // kasih link prosesnya
RecyclerView mRecyclerView;
RecyclerView.Adapter mAdapter;
RecyclerView.LayoutManager mManager;
ProgressDialog pd;
ArrayList<ModelData> mItems;
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
return inflater.inflate(R.layout.fragment_kecamatan, container, false);
mRecyclerView = (RecyclerView) mRecyclerView.findViewById(R.id.list_data); <-- Unreachable statement
mItems = new ArrayList<>();
mRecyclerView.setLayoutManager(new GridLayoutManager(getActivity(), 3));
mAdapter = new AdapterProcess(KecamatanFragment.this, mItems);
mRecyclerView.setAdapter(mAdapter);
loadjson();
}
enter code here
//proses mengambil data
private void loadjson(){
pd.setMessage("Mengambil Data");
pd.setCancelable(false);
pd.show();
JsonArrayRequest arrayRequest = new JsonArrayRequest(Request.Method.POST, data_url, null, new Response.Listener<JSONArray>() {
#Override
public void onResponse(JSONArray response) {
pd.cancel();
Log.d("volley", "response : " + response.toString());
for (int i=0; i < response.length(); i++){
try {
JSONObject data = response.getJSONObject(i);
ModelData md = new ModelData();
md.setKecamatan(data.getString("kecamatan")); // memanggil nama array yang kita buat
mItems.add(md);
} catch (JSONException e) {
e.printStackTrace();
}
}
mAdapter.notifyDataSetChanged();
}
}, new Response.ErrorListener(){
#Override
public void onErrorResponse(VolleyError error) {
pd.cancel();
Log.d("volley", "error : " + error.getMessage());
}
});
Controller.getInstance().addToRequestQueue(arrayRequest);
}
}

Unreachable statement
That's expected error, because you're stopping the onCreateView method after you're giving it a return statement:
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
// You've already close the method when you're giving a return
return inflater.inflate(R.layout.fragment_kecamatan, container, false);
// so this won't be reachable, hence the unreachable error raised.
mRecyclerView = (RecyclerView) mRecyclerView.findViewById(R.id.list_data);
...
}
So, you either need to inflate the Layout first and bind the view then return the inflated view or move the view binding after the return statement to another method.

As mentioned by ישו אוהב אותך, You're returning the inflated view immediately. keep a reference to the inflated view and return it at the end. Also, you probably want to use findViewById on the inflated view and not on mRecyclerView.
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.fragment_kecamatan, container, false);
mRecyclerView = (RecyclerView) view.findViewById(R.id.list_data);
mItems = new ArrayList<>();
mRecyclerView.setLayoutManager(new GridLayoutManager(getActivity(), 3));
mAdapter = new AdapterProcess(KecamatanFragment.this, mItems);
mRecyclerView.setAdapter(mAdapter);
loadjson();
return view;
}

RecyclerView is a null in fragment

I have MainActivity,which contain viewpager,which contain 2 fragments:
MainActivity
ViewPager viewPager = findViewById(R.id.viewPager);
MyPagerAdapter adapter = new MyPagerAdapter(this,
getSupportFragmentManager());
viewPager.setAdapter(adapter);
TabLayout tabLayout = findViewById(R.id.TabLayout);
tabLayout.setupWithViewPager(viewPager);
Fragment fragmentHour=adapter.getItem(1);
onChangeDayListener2= (OnChangeDayListener) fragmentHour;
I am also have interface for send data from main activity in fragment:
public interface OnChangeDayListener{
void OnChange(WeatherList list,int pos);
}
but when i try to work with this callback in interface my recycler adapter always is null:
HourWeatherFragment:
public class HourWeatherFragment extends Fragment implements MainScreen.OnChangeDayListener{
private RecyclerView recyclerView;
private AdapterHour adapter;
private ArrayList<Weather> days;
Context context;
static HttpClient httpClient;
public HourWeatherFragment() {
// Required empty public constructor
}
#Override
public void onActivityCreated(#Nullable Bundle savedInstanceState) {
super.onActivityCreated(savedInstanceState);
days=new ArrayList<>();
adapter = new AdapterHour(days,getActivity());
LinearLayoutManager LayoutManager = new LinearLayoutManager(getActivity().getBaseContext(),
LinearLayoutManager.VERTICAL, false);
recyclerView.setLayoutManager(LayoutManager);
recyclerView.setAdapter(adapter);
days.add(new Weather());
recyclerView.getAdapter().notifyDataSetChanged();
Log.d("recycler","adapter seted!");
}
#Override
public void onViewCreated(#NonNull View view, #Nullable Bundle savedInstanceState) {
super.onViewCreated(view, savedInstanceState);
}
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
// Inflate the layout for this fragment
View rootView = inflater.inflate(R.layout.fragment_hour_weather, container, false);
recyclerView = rootView.findViewById(R.id.hour_list);
httpClient=new HttpClient();
MyAsyncTask task=new MyAsyncTask();
// task.execute("lviv");
return rootView;
}
#Override
public void onAttach(Context context) {
super.onAttach(context);
this.context=context;
}
#Override
public void OnChange(WeatherList list,int pos) {
String date=list.getAverageWeather().get(pos).getDate();
ArrayList<Weather> weather=list.getByDate(date);
Log.d("ldata","size of weather for adding="+weather.size());
// days.add(new Weather());
if(adapter!=null){
adapter.notifyDataSetChanged();
Log.d("tag","first null!");}
else{
try{
recyclerView.getAdapter();}
catch (NullPointerException ex){
Log.d("tag","null!");//THERE ALWAYS NULL
}}
So,firstly creating activity,then i start load data and when data loaded i send data from MainActivity to HourWeatherFragment throught callback,
but when i receive data in fragment,my adapter is null,how i can fix it?

You can create a static singleton class to hold data and retrieve that data in the fragment.
public class DataHolder {
//create static variables here.
}
In your fragment simply retrieve the data and make it null after that.
Alternative solution
Another solution is to use Bundles. Follow the bundle solution here.

You must cast RecyclerView.
in your fragment and onCreateView method :
recyclerView = (RecyclerView) rootView.findViewById(R.id.hour_list);

I know this is an old question, but contrary to the accepted answer I think the issue is that the handle to the fragment's widget such as recyclerView is not available in the OnCreateView function.
The handles (or pointers if you wish) to the widgets are only guaranteed to exist in the OnViewCreated function.
This documentation has good description of the lifecycle of fragments:
https://guides.codepath.com/android/Creating-and-Using-Fragments
an extract is:
// This event is triggered soon after onCreateView().
// onViewCreated() is only called if the view returned from onCreateView() is non-null.
// Any view setup should occur here. E.g., view lookups and attaching view listeners.
#Override
public void onViewCreated(View view, Bundle savedInstanceState) {
super.onViewCreated(view, savedInstanceState);
ListView lv = (ListView) view.findViewById(R.id.lvSome);
lv.setAdapter(adapter);
}
Hope this helps.

RecyclerView not working with fragment

I try to create a HORIZONTAL recyclerView but recyclerView can't find the context here is my Fragmnet code:
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
this.context =context;
if (getArguments() != null) {
mParam1 = getArguments().getString(ARG_PARAM1);
mParam2 = getArguments().getString(ARG_PARAM2);
}
}
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
// Inflate the layout for this fragment
ArrayList<CategoryModel> categoryModels = null;
RecyclerView recyclerView = container.findViewById(R.id.category_recycler);
// recyclerView.setHasFixedSize(true);
CategoryAdapter adapter = new CategoryAdapter(context,CategoryData.getCategory());
recyclerView.setAdapter(adapter);
LinearLayoutManager layoutManager = new LinearLayoutManager(getActivity());
layoutManager.setOrientation(LinearLayoutManager.HORIZONTAL);
recyclerView.setLayoutManager(layoutManager);
return inflater.inflate(R.layout.main_fragment, container, false);
}
and here is Recycler view adapter code:
public class CategoryAdapter extends RecyclerView.Adapter<CategoryAdapter.ViewHolder> {
Context context;
ArrayList<CategoryModel> categorys;
public CategoryAdapter(Context context, ArrayList<CategoryModel> categoryModels) {
this.categorys = categoryModels;
this.context = context;
}
#NonNull
#Override
public CategoryAdapter.ViewHolder onCreateViewHolder(#NonNull ViewGroup parent, int viewType) {
View view = LayoutInflater.from(context).inflate(R.layout.product_category,parent,false);
return new ViewHolder(view);
}
i'm also attached the Debug result please check the image

Try like this:
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup parent, Bundle savedInstanceState) {
// Defines the xml file for the fragment
return inflater.inflate(R.layout.main_fragment, parent, false);
}
#Override
public void onViewCreated(View view, Bundle savedInstanceState) {
// Inflate the layout for this fragment
ArrayList<CategoryModel> categoryModels = null;
RecyclerView recyclerView = view.findViewById(R.id.category_recycler);
// recyclerView.setHasFixedSize(true);
CategoryAdapter adapter = new CategoryAdapter(getContext(), CategoryData.getCategory());
LinearLayoutManager layoutManager = new LinearLayoutManager(getActivity());
layoutManager.setOrientation(LinearLayoutManager.HORIZONTAL);
recyclerView.setLayoutManager(layoutManager);
recyclerView.setAdapter(adapter);
}

To use Context inside Fragment use getContext() method .
CategoryAdapter adapter = new CategoryAdapter(getContext(),CategoryData.getCategory());
From official doc
Return the Context this fragment is currently associated with.
If you are using Context only for inflating view inside onCreateViewHolder method in CategoryAdapter class then you don't need to pass Context in Constructor. You can get Context from ViewGroup which is first parameter of the onCreateViewHolder method.
View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.product_category,parent,false);

In your onCreate() fragment callback I see this line:
public void onCreate(Bundle savedInstanceState) {
...
this.context =context;
...
}
This line doesn't do anything; there's no context argument to the onCreate() method or anything like that, so you're just assigning a variable back to itself. Since your Context context field doesn't have an explicit intialization, the default is null. So this is the same as writing
public void onCreate(Bundle savedInstanceState) {
...
this.context = null;
...
}
Later on, in onCreateView(), you're instantiating your adapter with this line:
CategoryAdapter adapter = new CategoryAdapter(context,CategoryData.getCategory());
Because of what I said above, this is functionally the same as
CategoryAdapter adapter = new CategoryAdapter(null, CategoryData.getCategory());
To solve this, you need some place to get a Context instance from. Fragments are often "attached" to a context, and, when they're attached, you can get that context by calling getContext(). A fragment is guaranteed to be attached to a context in the onActivityCreated() callback, so you will want to move your adapter creation to that callback instead of onViewCreated().
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
return inflater.inflate(R.layout.main_fragment, container, false);
}
#Override
public void onActivityCreated(Bundle savedInstanceState) {
super.onActivityCreated(savedInstanceState);
CategoryAdapter adapter = new CategoryAdapter(getContext(), CategoryData.getCategory());
LinearLayoutManager layoutManager = new LinearLayoutManager(getActivity());
layoutManager.setOrientation(LinearLayoutManager.HORIZONTAL);
RecyclerView recyclerView = getView().findViewById(R.id.category_recycler);
recyclerView.setAdapter(adapter);
recyclerView.setLayoutManager(layoutManager);
}

application null object reference

Previous Question:
May I know why this error will occur when I try to start RecyclerView activity doing a search from fragment.
After added adapter:
error: OwnerDAO.getOwner()' on a null object reference
Fragment code:
RecyclerView recyclerView;
RecyclerView.LayoutManager layoutManager;
SearchAdapter adapter;
OwnerDAO mOwnerDao;
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
// Inflate the layout for this fragment
View v = inflater.inflate(R.layout.activity_search, container, false);
recyclerView = (RecyclerView)v.findViewById(R.id.recycler_search);
layoutManager = new LinearLayoutManager(this.getActivity());
mOwnerDao = new OwnerDAO(getContext())
adapter = new SearchAdapter(getContext(),mOwnerDao.getOwner());
recyclerView.setLayoutManager(layoutManager);
recyclerView.setHasFixedSize(true);
recyclerView.setAdapter( adapter );
return v;
}
Search Adapter:
public SearchAdapter(Context context, List<Owner> owners) {
this.context = context;
this.owners = owners;
}

Set the layoutManager after setAdapter like this :-
recyclerView.setAdapter( adapter );
recyclerView.setLayoutManager(layoutManager);
The error will be removed !!