Null pointer exception when trying to pass a customAdapter?

Question

public class JsonViewpager  {
private VolleySingleton mVolleySingleton;
private ViewpagerAdapter mViewpagerAdapter;
private RequestQueue mRequestQueue;
private String mUrl;
private ArrayList<QuestionData> mQuestionDataArrayList = new      ArrayList<QuestionData>();

public JsonViewpager(ViewpagerAdapter viewpagerAdapter,String url){
    mViewpagerAdapter=viewpagerAdapter;
    mUrl=url;
}
public void JsonRequestMethod() {
    mVolleySingleton = VolleySingleton.getInstance();
    mRequestQueue = mVolleySingleton.getRequestQueue();
    JsonArrayRequest request = new JsonArrayRequest(Request.Method.GET, mUrl, (String) null, new Response.Listener<JSONArray>() {
        @Override
        public void onResponse(JSONArray response) {
            Parse parseJSONResponse=new Parse();
            mQuestionDataArrayList = parseJSONResponse(response);
            mViewpagerAdapter.setBloglist(mQuestionDataArrayList);
        }

    }, new Response.ErrorListener() {
        @Override
        public void onErrorResponse(VolleyError error) {
        }
    });
    mRequestQueue.add(request);
}
}

I have another class in which I am passing a viewPagerAdapter from, I set the viewPagerAdapter in the onCreateView in my other class, for some reason I am getting a null pointer exception when at mViewpagerAdapter.setBloglist(mQuestionDataArrayList); line. Does anyone know what is causing this?

Home Class

public class Home extends Fragment {
private static final int REFRESH_DELAY=500;
private static final String ARG_PARAM1 = "param1";
private static final String ARG_PARAM2 = "param2";
//URL reflects ordered list on server filter terms {"include": {"relation": "questions", "scope": {"order" : "points DESC"}}})
private static final String URL_HOME="hiddenUrl";

private String mParam1;
private String mParam2;
private ImageView mImageView;
private VolleySingleton mVolleySingleton;
private RequestQueue mRequestQueue;
private RecyclerView mRecyclerView;

private ArrayList<QuestionData> mListblogs = new ArrayList<>();
private ArrayList<QuestionData> mQuestionDataArrayList = new     ArrayList<QuestionData>();
private PullToRefreshView mPullToRefreshView;
private ViewpagerAdapter mViewpagerAdapter;

public static Home newInstance(String param1, String param2) {
    Home fragment = new Home();
    Bundle args = new Bundle();
    args.putString(ARG_PARAM1, param1);
    args.putString(ARG_PARAM2, param2);
    fragment.setArguments(args);
    return fragment;

}

public Home() {
    // Required empty public constructor
}

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    if (getArguments() != null) {
        mParam1 = getArguments().getString(ARG_PARAM1);
        mParam2 = getArguments().getString(ARG_PARAM2);
    }
    //If you wish to handle you event source in the activity main thread, you’ll need to add the following instructions at the beginning of the onCreate() android callback:
    System.out.println("userId" + Login.getUserId());
    System.out.println("username" + Login.getUserName());
    JsonViewpager s=new JsonViewpager(mViewpagerAdapter,URL_HOME);
    s.JsonRequestMethod();
}
 @Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {
    // Inflate the layout for this fragment
    View view = inflater.inflate(R.layout.fragment_home, container, false);
    mRecyclerView = (RecyclerView) view.findViewById(R.id.fragment_dashboard_recycler);
    mRecyclerView.setLayoutManager(new LinearLayoutManager(getActivity()));
    mViewpagerAdapter = new ViewpagerAdapter(getActivity());

    mRecyclerView.setAdapter((mViewpagerAdapter));
    mPullToRefreshView = (PullToRefreshView) view.findViewById(R.id.pull_to_refresh);

    mPullToRefreshView.setOnRefreshListener(new PullToRefreshView.OnRefreshListener() {
        @Override
        public void onRefresh() {
            mPullToRefreshView.postDelayed(new Runnable() {
                @Override
                public void run() {
                    mPullToRefreshView.setRefreshing(false);
                    JsonRequestMethod();
                }
            }, REFRESH_DELAY);
        }
    });
    return view;
}
}

only way is if the class that instantiated this object passed `null`. — Matt Clark, May 25 '16 at 00:11
Right, I think it is passing a null reference, but I dont see why? — Eli, May 25 '16 at 00:11
For instance, if I put this request in my class that is passing a null reference, then it will work — Eli, May 25 '16 at 00:12
you have not shown us the could that might explain _why_. please [edit] your question to include the code that instantiates this object. — Matt Clark, May 25 '16 at 00:12
In my onCreate of my other class I do this though JsonViewpager s=new JsonViewpager(mViewpagerAdapter,URL_HOME); s.JsonRequestMethod(); — Eli, May 25 '16 at 00:12

Matt Clark · Accepted Answer · 2016-05-25T04:58:43.580

1

You are calling

JsonViewpager s=new JsonViewpager(mViewpagerAdapter,URL_HOME);

in the onCreate method, and then

mViewpagerAdapter = new ViewpagerAdapter(getActivity());

in the onCreateView method.

The problem is that in the activity lifecycle, onCreateVeiw will come AFTER onCreate, meaning that your JsonViewepager object was created passing in a null for the value of mViewpagerAdapter.

For reference:

edited May 25 '16 at 04:58

answered May 25 '16 at 00:17

Matt Clark

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Awesome, thanks, I have not review the lifecycle in a while, thank you! – Eli May 25 '16 at 00:20

Null pointer exception when trying to pass a customAdapter?

1 Answers1