Java 不是封闭类错误

我正试图设置适配器，但它给我的错误不是下面一行的onCreateView方法中的封闭类

CustomAdapter adapter = new CustomAdapter(SecondYearFragment.this, sub);      

这是我的activity.xml

<android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:id="@+id/container"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".MainActivity">

<FrameLayout
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:id="@+id/content_main">

</FrameLayout>

<android.support.design.widget.BottomNavigationView
    android:id="@+id/navigation"
    android:layout_width="0dp"
    android:layout_height="wrap_content"
    android:layout_marginEnd="0dp"
    android:layout_marginStart="0dp"
    android:background="?android:attr/windowBackground"
    app:layout_constraintBottom_toBottomOf="parent"
    app:layout_constraintLeft_toLeftOf="parent"
    app:layout_constraintRight_toRightOf="parent"
    app:menu="@menu/navigation" />

这是我的自定义适配器

public  class CustomAdapter extends ArrayAdapter<String> {
String[] subjects;
Context mContext;

public CustomAdapter(@NonNull Context context, String[] subjects) {
    super(context, R.layout.sec_year_dept);
    this.subjects = subjects;
    this.mContext = context;
}

@Override
public int getCount() {
    return subjects.length;   //returns the size of the list
}

@NonNull
@Override
public View getView(int position, @Nullable View convertView, @NonNull ViewGroup parent) {
    ViewHolder mViewHolder = new ViewHolder();
    if(convertView == null) {
        LayoutInflater mInflator = (LayoutInflater) mContext.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
        convertView = mInflator.inflate(R.layout.sec_year_dept, parent, false);
        mViewHolder.mSubjects = (TextView) convertView.findViewById(R.id.dept_name);
        mViewHolder.mSubjects.setText(subjects[position]);
        convertView.setTag(mViewHolder);
    }else {
        mViewHolder = (ViewHolder) convertView.getTag();
    }
    return convertView;
}
static class ViewHolder {
    TextView mSubjects;
}}

公共类CustomAdapter扩展了ArrayAdapter{
字符串[]主题；
语境；
公共CustomAdapter（@NonNull上下文，字符串[]主题）{
super（背景、右布局、部门）；
这个。主题=主题；
this.mContext=上下文；
}
@凌驾
public int getCount（）{
return subjects.length；//返回列表的大小
}
@非空
@凌驾
公共视图getView（int位置，@Nullable视图convertView，@NonNull视图组父级）{
ViewHolder MVIEHOLDER=新的ViewHolder（）；
if（convertView==null）{
LayoutInflater mInflator=（LayoutInflater）mContext.getSystemService（Context.LAYOUT\u INFLATER\u SERVICE）；
convertView=mInflator.充气（R.layout.sec\u year\u dept，parent，false）；
mViewHolder.mSubjects=（TextView）convertView.findViewById（R.id.dept_name）；
mViewHolder.mSubjects.setText（受试者[位置]）；
setTag（mViewHolder）；
}否则{
mViewHolder=（ViewHolder）convertView.getTag（）；
}
返回视图；
}
静态类视窗夹{
text查看mSubjects；
}}

有人能告诉我发生了什么事，我错过了什么吗

试试这个：

CustomAdapter adapter = new CustomAdapter(this.getContext(), sub); 

您引用的片段未在当前片段

SecondYearFragment

中实例化。所以它还没有上下文

---

此外，片段不是上下文，因此即使实例化它也无法工作。

使用

CustomAdapter=newcustomadapter（getContext（），sub）

您使用的语法用于访问匿名类中的封闭类实例。ThirdYearFragment不是SecondYearFragment的封闭类，这就是为什么会出现此错误
 此行的Becz CustomAdapter adapter=新的CustomAdapter（SecondYearFragment.this，sub）；使用此而不是SecondYearFragment.this。是的，它正在崩溃应用程序，并说空引用。所以在片段上设置自定义适配器不起作用？
public class ThirdYearFragment extends Fragment {
private static final String ARG_PARAM1 = "param1";
private static final String ARG_PARAM2 = "param2";

ListView mListview;
String[] sub = {"random1", "random2", "random3", };

// TODO: Rename and change types of parameters
private String mParam1;
private String mParam2;

private OnFragmentInteractionListener mListener;

public ThirdYearFragment() {
    // Required empty public constructor
}

public static ThirdYearFragment newInstance(String param1, String param2) {
    ThirdYearFragment fragment = new ThirdYearFragment();
    Bundle args = new Bundle();
    args.putString(ARG_PARAM1, param1);
    args.putString(ARG_PARAM2, param2);
    fragment.setArguments(args);
    return fragment;
}

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    if (getArguments() != null) {
        mParam1 = getArguments().getString(ARG_PARAM1);
        mParam2 = getArguments().getString(ARG_PARAM2);
    }
}

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {


    // Inflate the layout for this fragment
    View view = inflater.inflate(R.layout.fragment_third_year, container, true);

    ListView listView = view.findViewById(R.id.listviewsecond);
    CustomAdapter adapter = new CustomAdapter(SecondYearFragment.this, sub);
    listView.setAdapter(adapter);
    return view;
} }

public  class CustomAdapter extends ArrayAdapter<String> {
String[] subjects;
Context mContext;

public CustomAdapter(@NonNull Context context, String[] subjects) {
    super(context, R.layout.sec_year_dept);
    this.subjects = subjects;
    this.mContext = context;
}

@Override
public int getCount() {
    return subjects.length;   //returns the size of the list
}

@NonNull
@Override
public View getView(int position, @Nullable View convertView, @NonNull ViewGroup parent) {
    ViewHolder mViewHolder = new ViewHolder();
    if(convertView == null) {
        LayoutInflater mInflator = (LayoutInflater) mContext.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
        convertView = mInflator.inflate(R.layout.sec_year_dept, parent, false);
        mViewHolder.mSubjects = (TextView) convertView.findViewById(R.id.dept_name);
        mViewHolder.mSubjects.setText(subjects[position]);
        convertView.setTag(mViewHolder);
    }else {
        mViewHolder = (ViewHolder) convertView.getTag();
    }
    return convertView;
}
static class ViewHolder {
    TextView mSubjects;
}}

CustomAdapter adapter = new CustomAdapter(this.getContext(), sub);