问题
I am getting some news data from my CMS,and want to display them in a RecyclerView.The problem is that I am getting a null pointer exception in the line where I using the LinearLayoutManager. Here is the logcat output.
Caused by: java.lang.NullPointerException
at testing.theo.manchesterunitedapp.newsandfeatures.FeaturesFragment.onCreateView(FeaturesFragment.java:65)
at android.support.v4.app.Fragment.performCreateView(Fragment.java:1962)
at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1067)
at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1248)
at android.support.v4.app.BackStackRecord.run(BackStackRecord.java:738)
at android.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1613)
at android.support.v4.app.FragmentController.execPendingActions(FragmentController.java:330)
at android.support.v4.app.FragmentActivity.onStart(FragmentActivity.java:547)
at android.app.Instrumentation.callActivityOnStart(Instrumentation.java:1171)
at android.app.Activity.performStart(Activity.java:5241)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2157)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2233)
at android.app.ActivityThread.access$800(ActivityThread.java:135)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:136)
at android.app.ActivityThread.main(ActivityThread.java:5001)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:515)
The Fragment where I am doing the webservice part is quite simple. I use to callback methods. The onCreateView where I am initialising the ArrayList and the RecyclerView,and secondly the onActivityCreate where I am running the webservice.
public class FeaturesFragment extends Fragment {
public static final String TAG = "ManuApp";
private static final String IMAGE_URL = "xxxxxxxxxxxx/xxxx/features_images/" ;
private List<FeaturesObject> listItemsList;
private RecyclerView mRecyclerView;
private FeaturesAdapter adapter;
public FeaturesFragment() {
// Required empty public constructor
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View v = inflater.inflate(R.layout.features_row, container, false);
// Inflate the layout for this fragment
listItemsList = new ArrayList<>();
mRecyclerView = (RecyclerView)v.findViewById(R.id.features_recycler_view);
//mRecyclerView.addItemDecoration(new HorizontalDividerItemDecoration.Builder(getActivity()).color(Color.BLACK).build());
final LinearLayoutManager linearLayoutManager = new LinearLayoutManager(getActivity());
mRecyclerView.setLayoutManager(linearLayoutManager);
return v;
}
@Override
public void onActivityCreated(Bundle savedInstanceState) {
super.onActivityCreated(savedInstanceState);
updateFeaturesList();
}
public void updateFeaturesList() {
//declare the adapter and attach it to the recyclerview
adapter = new FeaturesAdapter(getActivity(), listItemsList);
mRecyclerView.setAdapter(adapter);
// Instantiate the RequestQueue.
RequestQueue queue = Volley.newRequestQueue(getActivity());
// Request a string response from the provided URL.
JsonArrayRequest jsObjRequest = new JsonArrayRequest(Request.Method.GET, Config.URL_FEATURES, new Response.Listener<JSONArray>() {
@Override
public void onResponse(JSONArray response) {
Log.d(TAG, response.toString());
//hidePD();
// Parse json data.
// Declare the json objects that we need and then for loop through the children array.
// Do the json parse in a try catch block to catch the exceptions
try {
for (int i = 0; i < response.length(); i++) {
JSONObject post = response.getJSONObject(i);
FeaturesObject item = new FeaturesObject();
item.setTitle(post.getString("title"));
item.setImage(IMAGE_URL + post.getString("features_image"));
item.setArticle(post.getString("article"));
listItemsList.add(item);
}
} catch (JSONException e) {
e.printStackTrace();
}
// Update list by notifying the adapter of changes
adapter.notifyDataSetChanged();
}
}, new Response.ErrorListener() {
@Override
public void onErrorResponse(VolleyError error) {
VolleyLog.d(TAG, "Error: " + error.getMessage());
//hidePD();
}
});
jsObjRequest.setRetryPolicy(new RetryPolicy() {
@Override
public int getCurrentTimeout() {
return 50000;
}
@Override
public int getCurrentRetryCount() {
return 50000;
}
@Override
public void retry(VolleyError error) throws VolleyError {
}
});
queue.add(jsObjRequest);
}
}
This part of the code causes the problem.
final LinearLayoutManager linearLayoutManager = new LinearLayoutManager(getActivity());
mRecyclerView.setLayoutManager(linearLayoutManager);
This is strange,as I am using the same techiques to obtain data in another fragment of my app.
Any ideas?
Thanks.
回答1:
Your RecyclerView is null. Are you sure you're looking for the correct id in the correct layout file? My guess is either you are inflating the incorrect layout file, or you're looking for the incorrect view id for the RecyclerView.
回答2:
Probably this is not the case but... As a general rule all initialization that need instance of the activity must be in onActivityCreated() (or the next methods in the Fragment lifecycle). Inside onCreateView() getActivity() is not guaranteed to return non-null value. In some scenarios it returns null.
回答3:
Seems like the id that you are trying to find it's not on features_row that's why you get NullPointerException on that line :
mRecyclerView = (RecyclerView)v.findViewById(R.id.features_recycler_view);
If you keep getting error you could try this :
final FragmentActivity c = getActivity();
final LinearLayoutManager linearLayoutManager = new LinearLayoutManager(c);
mRecyclerView.setLayoutManager(linearLayoutManager );
来源：https://stackoverflow.com/questions/35489177/recyclerview-with-null-pointer-exception