ViewPager and NullObjectReference error

Question

我在将适配器设置为ViewPager方面有问题。每次我遇到NullObjectReference错误。我的代码怎么了？

1）布局：

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical">
<android.support.v4.view.ViewPager
    android:id="@+id/view_pager"
    android:layout_width="match_parent"
    android:layout_height="wrap_content">
    <android.support.v4.view.PagerTabStrip
        android:id="@+id/pager_header"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_gravity="top"
        android:paddingBottom="4dp"
        android:paddingTop="4dp" />
</android.support.v4.view.ViewPager>
</LinearLayout>

2）Java类：

public class FoodFragment extends Fragment {
Toolbar toolbar;
ViewPager viewPager;
TabsPagerAdapter pagerAdapter;

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {
    setRetainInstance(true);
      ((AppCompatActivity)getActivity())
    .getSupportActionBar().setDisplayShowTitleEnabled(true);
    ((AppCompatActivity)getActivity())
    .getSupportActionBar().setTitle(R.string.food);
    toolbar = (Toolbar) getActivity().findViewById(R.id.toolbar);
    toolbar.setBackgroundColor(Color.parseColor("#f6a632"));
    pagerAdapter = new    TabsPagerAdapter(getActivity()
   .getSupportFragmentManager());
    viewPager = (ViewPager) getActivity().findViewById(R.id.view_pager);
    viewPager.setAdapter(pagerAdapter);
    return inflater.inflate(R.layout.fragment_food, container, false);
}
}

调用viewPager.setAdapter（pageradapter）时，我总是会遇到此错误；线。

Answer 1

原因是您的OtCreateview。在片段中，您首先需要首先夸大片段的视图，然后从此视图中找到ViewByid。您可能会在下面看到一个示例：

@Nullable
@Override
public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
    // Inflate the layout for this fragment
    View rootView = inflater.inflate(R.layout.fragment_food, container, false);
    // get your view by: rootView.findViewById()
    // for example:
    viewPager = (ViewPager) rootView.findViewById(R.id.view_pager);
    // do others...
    return rootView;
}