调用函数/方法时出错？

Question

For some reason I am getting an error when i invoke the addFrag function/method to populate my fragment and string title. I am creating a simple ViewPager with an adapter. This is all in a fragment by the way. Here is the code:

public class HomeFragment extends Fragment {

    private View view;
    private ViewPager viewPager;
    private TabLayout tabLayout;
    private PagerAdapter adapter;

    @Override
    public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup viewGroup,
                             @Nullable Bundle savedInstanceState) {
        view = inflater.inflate(R.layout.home_fragment, viewGroup, false);

        viewPager = (ViewPager) view.findViewById(R.id.viewpager);
        setUpViewPager(viewPager);

        tabLayout = (TabLayout) view.findViewById(R.id.sliding_tabs);
        tabLayout.post(new Runnable() {
            @Override
            public void run() {
                tabLayout.setupWithViewPager(viewPager);
            }
        });
        return view;
    }



    private void setUpViewPager(ViewPager viewPager) {
        adapter = new ViewPagerAdapter(getChildFragmentManager());
        adapter.addFrag(new ContentFragment(), "ONE");
        adapter.addFrag(new ContentFragment(), "TWO");
        adapter.addFrag(new ContentFragment(), "THREE");
        viewPager.setAdapter(adapter);
    }


}

class ViewPagerAdapter extends FragmentPagerAdapter{
    private final List<Fragment> fragmentList = new ArrayList<>();
    private final List<String> tabTitles = new ArrayList<>();

    //Default Fragment Constructor
    public ViewPagerAdapter(FragmentManager fm) {
        super(fm);
    }


    @Override
    public Fragment getItem(int position) {
        return fragmentList.get(position);
    }

    @Override
    public int getCount() {
        return fragmentList.size();
    }
    public void addFrag(Fragment fragment, String title){
        fragmentList.add(fragment);
        tabTitles.add(title);
    }
    @Override
    public CharSequence getPageTitle(int position){
        return tabTitles.get(position);
    }

}

When I try to type adapter.addFrag(new ExampleFragment(), "Hello"); I get an error cannot resolve method addFrag. Any help will be appreciated.

Answer 1

adapter is declared as a PagerAdapter , not a ViewPagerAdapter . Therefore the only methods you can use on adapter are the ones defined for PagerAdapter . The compiler doesn't know that adapter will actually be a ViewPagerAdapter at that point--I can tell that it will, because I saw the assignment adapter = new ViewPagerAdapter(...) up above, but the compiler isn't allowed to notice that (those are the rules of the language). Instead:

ViewPagerAdapter viewPagerAdapter = new ViewPagerAdapter(getChildFragmentManager());

Use viewPagerAdapter to call your addFrag methods, and eventually assign adapter = viewPagerAdapter; .

Answer 2

Change private PagerAdapter adapter; to private ViewPagerAdapter adapter;

OR

Type cast adapter to ViewPagerAdapter and then call addFlag

((ViewPagerAdapter)adapter).addFlag(new ContentFragment(), "ONE");