尝试传递customAdapter时是否为空指针异常？

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);
}
}

我有另一个类，我在其中传递一个viewPagerAdapter，我在我的其他类的onCreateView中设置了viewPagerAdapter，由于某种原因，我在mViewpagerAdapter.setBloglist（mQuestionDataArrayList）时得到一个空指针异常;线。有谁知道造成这种情况的原因是什么？

家庭课程

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;
}
}

Answer 1

您正在致电

JsonViewpager s=new JsonViewpager(mViewpagerAdapter,URL_HOME);

在onCreate方法中，然后

mViewpagerAdapter = new ViewpagerAdapter(getActivity());

在onCreateView方法中。

问题在于，在活动生命周期中，onCreateVeiw将在onCreate之后出现，这意味着您的JsonViewepager对象已创建，传递的值为mViewpagerAdapter。

reference：