非空ListView给出无效索引0的错误，大小为0

Question

我有一个ListView片段，我在其中注册了ListView以获取上下文菜单：

CourseArrayAdapter adapter = new CourseArrayAdapter(getActivity(), register.getCourseListByGrade(grade));
    setListAdapter(adapter);
    getListView().setLongClickable(true);
    registerForContextMenu(getListView());

我确信我的适配器包含非空列表，因为ListView中填充了我的自定义视图。

上下文菜单相关方法：

    @Override
public void onCreateContextMenu(ContextMenu menu, View v, ContextMenu.ContextMenuInfo menuInfo) {
    MenuInflater inflater = getActivity().getMenuInflater();
    inflater.inflate(R.menu.menu_course_context, menu);
    AdapterView.AdapterContextMenuInfo info = (AdapterView.AdapterContextMenuInfo)menuInfo;
    menu.setHeaderTitle(((CourseArrayAdapter)getListAdapter()).getItem(info.position).getCourseName());
}

@Override
public boolean onContextItemSelected(MenuItem item) {

    switch (item.getItemId()) {
        case R.id.action_remove:
            register.removeCourse(((CourseArrayAdapter) getListAdapter()).getItem(((AdapterView.AdapterContextMenuInfo) item.getMenuInfo()).position).getId());
            return true;
        case R.id.action_edit:
            register.editCourse(((CourseArrayAdapter) getListAdapter()).getItem(((AdapterView.AdapterContextMenuInfo) item.getMenuInfo()).position).getId());
            return true;
    }
    return super.onContextItemSelected(item);
}

在getListAdapter().getItem(info.position)中调用onCreatedContextMenu无误地运行，并显示正确的菜单标题。但是，单击选项时会显示以下错误：

08-14 16:02:46.964 1923-1923/com.andhruv.schoolapp E/MessageQueue-JNI﹕ java.lang.IndexOutOfBoundsException: Invalid index 0, size is 0 at java.util.ArrayList.throwIndexOutOfBoundsException(ArrayList.java:255) at java.util.ArrayList.get(ArrayList.java:308) at android.widget.ArrayAdapter.getItem(ArrayAdapter.java:337) at com.andhruv.schoolapp.CourseListFragment.onContextItemSelected(CourseListFragment.java:62) at android.support.v4.app.Fragment.performContextItemSelected(Fragment.java:1912)

CourseListFragment.java:62是

行

register.editCourse(((CourseArrayAdapter) getListAdapter()).getItem(((AdapterView.AdapterContextMenuInfo) item.getMenuInfo()).position).getId());

CourseArrayAdapter：

class CourseArrayAdapter extends ArrayAdapter<Course> {
private Gpa gpaCalculator;

public CourseArrayAdapter(Context context, List<Course> values) {
    super(context, 0,values);
    gpaCalculator = new Gpa();
}

@Override
public  View getView(int position, View convertView, ViewGroup parent) {
    LayoutInflater inflater = (LayoutInflater)getContext().getSystemService(Context.LAYOUT_INFLATER_SERVICE);
    View rowView = inflater.inflate(R.layout.item_course,parent,false);
    TextView textViewCourseName = (TextView)rowView.findViewById(R.id.textViewCourseName);
    TextView textViewGpa = (TextView)rowView.findViewById(R.id.textViewGpa);
    TextView textViewGrade = (TextView)rowView.findViewById(R.id.textViewGrade);
    TextView textViewType = (TextView)rowView.findViewById(R.id.textViewType);
    TextView textViewCategory = (TextView)rowView.findViewById(R.id.textViewCategory);
    textViewCourseName.setText(getItem(position).getCourseName());
    textViewGpa.setText(String.valueOf(gpaCalculator.calcCourseVal(getItem(position).getLetterGrade(),getItem(position).getCourseLevel(),true)));
    textViewType.setText(String.valueOf(getItem(position).getCourseLevel()));
    textViewCategory.setText(String.valueOf(getItem(position).getCategory()).replace('_',' '));
    textViewGrade.setText(String.valueOf(getItem(position).getLetterGrade()));
    textViewCourseName.setTag(getItem(position).getId());
    return rowView;
}

}

为什么调用((CourseArrayAdapter)getListAdapter()).getItem(info.position)在onCreateContextMenu中工作但在onContextItemSelected中不起作用？