我试图在片段中使用recyclelerView，但每当我运行应用程序时，我在视图上调用setLayoutManager时会得到一个nullpointer异常。我跟着android文件使用了recyclelerview和片段，并在这里查看了与此问题相关的帖子，但似乎没有任何效果。
`07-09 17：40：27.784 4565-4565 / com.example.broulayedoumbia.restaurantapp E / AndroidRuntime： 致命异议：主要 过程：com.example.broulayedoumbia.restaurantapp，PID：4565 java.lang.RuntimeException：无法启动活动 ComponentInfo {com.example.broulayedoumbia.restaurantapp / com.example.broulayedoumbia.restaurantapp.MainActivity}： java.lang.NullPointerException：尝试调用虚方法＆＃39; void android.support.v7.widget.RecyclerView.setLayoutManager（android.support.v7.widget.RecyclerView $布局管理）＆＃39; 在null对象引用上 在 android.app.ActivityThread.performLaunchActivity（ActivityThread.java:2665） 在 android.app.ActivityThread.handleLaunchActivity（ActivityThread.java:2726） 在android.app.ActivityThread.-wrap12（ActivityThread.java） 在 android.app.ActivityThread $ H.handleMessage（ActivityThread.java:1477） 在android.os.Handler.dispatchMessage（Handler.java:102） 在android.os.Looper.loop（Looper.java:154） 在android.app.ActivityThread.main（ActivityThread.java:6119） at java.lang.reflect.Method.invoke（Native Method） 在 com.android.internal.os.ZygoteInit $ MethodAndArgsCaller.run（ZygoteInit.java:886） 在com.android.internal.os.ZygoteInit.main（ZygoteInit.java:776） 引起：java.lang.NullPointerException：尝试调用虚拟 方法＆＃39;无效 android.support.v7.widget.RecyclerView.setLayoutManager（android.support.v7.widget.RecyclerView $布局管理）＆＃39; 在null对象引用上 在 com.example.broulayedoumbia.restaurantapp.RestaurantListFragment.onCreateView（RestaurantListFragment.java:79） 在 android.support.v4.app.Fragment.performCreateView（Fragment.java:2192）
`
片段代码：
public class RestaurantListFragment extends Fragment implements RestaurantAdapter.ListItemClickListener{
private static final int NUM_LIST_ITEMS = 100;
private OnFragmentInteractionListener mListener;
private RestaurantAdapter mAdapter;
private RecyclerView mRestaurantList;
public RestaurantListFragment() {
// Required empty public constructor
}
/**
* Use this factory method to create a new instance of
* this fragment using the provided parameters.
*
* @param param1 Parameter 1.
* @param param2 Parameter 2.
* @return A new instance of fragment RestaurantListFragment.
*/
// TODO: Rename and change types and number of parameters
public static RestaurantListFragment newInstance(String param1, String param2) {
RestaurantListFragment fragment = new RestaurantListFragment();
Bundle args = new Bundle();
fragment.setArguments(args);
return fragment;
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.fragment_login, container, false);
/*
* Using findViewById, we get a reference to our RecyclerView from xml. This allows us to
* do things like set the adapter of the RecyclerView and toggle the visibility.
*/
mRestaurantList = (RecyclerView) view.findViewById(R.id.rest_list);
/*
* A LinearLayoutManager is responsible for measuring and positioning item views within a
* RecyclerView into a linear list. This means that it can produce either a horizontal or
* vertical list depending on which parameter you pass in to the LinearLayoutManager
* constructor. By default, if you don't specify an orientation, you get a vertical list.
* In our case, we want a vertical list, so we don't need to pass in an orientation flag to
* the LinearLayoutManager constructor.
*
* There are other LayoutManagers available to display your data in uniform grids,
* staggered grids, and more! See the developer documentation for more details.
*/
RecyclerView.LayoutManager layoutManager = new LinearLayoutManager(getActivity());
mRestaurantList.setLayoutManager(layoutManager);
/*
* Use this setting to improve performance if you know that changes in content do not
* change the child layout size in the RecyclerView
*/
mRestaurantList.setHasFixedSize(true);
mAdapter = new RestaurantAdapter(NUM_LIST_ITEMS, this);
mRestaurantList.setAdapter(mAdapter);
return view;
}
@Override
public void onAttach(Context context) {
super.onAttach(context);
if (context instanceof OnFragmentInteractionListener) {
mListener = (OnFragmentInteractionListener) context;
} else {
throw new RuntimeException(context.toString()
+ " must implement OnFragmentInteractionListener");
}
}
@Override
public void onDetach() {
super.onDetach();
mListener = null;
}
@Override
public void onListItemClick(int clickedItemIndex) {
}
/**
* This interface must be implemented by activities that contain this
* fragment to allow an interaction in this fragment to be communicated
* to the activity and potentially other fragments contained in that
* activity.
* <p>
* See the Android Training lesson <a href=
* "http://developer.android.com/training/basics/fragments/communicating.html"
* >Communicating with Other Fragments</a> for more information.
*/
public interface OnFragmentInteractionListener {
}
}
片段Xml：
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical">
<android.support.v7.widget.RecyclerView
android:id="@+id/rest_list"
android:layout_width="match_parent"
android:layout_height="match_parent"/>
主要活动：
public class MainActivity extends AppCompatActivity implements LoginFragment.OnFragmentInteractionListener, RestaurantListFragment.OnFragmentInteractionListener {
private LoginFragment loginFragment;
private RestaurantListFragment restaurantListFragment;
private FragmentTransaction fragmentManager;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
fragmentManager = getSupportFragmentManager().beginTransaction();
loginFragment = new LoginFragment();
restaurantListFragment = new RestaurantListFragment();
fragmentManager.replace(R.id.fragContainer, restaurantListFragment).commit();
}
@Override
public void login() {
}
}