具有空指针异常的RecyclerView [英] RecyclerView with null pointer exception
问题描述
我正在从CMS中获取一些新闻数据，并希望在RecyclerView中显示它们.问题是我在使用LinearLayoutManager的行中遇到了空指针异常.这是logcat的输出.
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)
我在其中做网络服务部分的片段非常简单.我使用回调方法.在其中初始化ArrayList和RecyclerView的onCreateView上，其次在运行Web服务的onActivityCreate上.
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);
}
}
这部分代码会导致问题.
This part of the code causes the problem.
final LinearLayoutManager linearLayoutManager = new LinearLayoutManager(getActivity());
mRecyclerView.setLayoutManager(linearLayoutManager);
这很奇怪，因为我使用相同的技术来获取应用程序另一个片段中的数据.
This is strange,as I am using the same techiques to obtain data in another fragment of my app.
有什么想法吗?
谢谢.
推荐答案
您的RecyclerView为空.您确定要在正确的布局文件中寻找正确的ID吗?我的猜测是您正在填充错误的布局文件，或者正在寻找RecyclerView的错误视图ID.
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.
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