java - 更改 ViewPager 内显示的 fragment

Question

我有 ViewPager 显示 fragment :SearchFragment、FriendFragment。我正在努力做的是将 SearchFragment 更改为 ChatFragment

replace-fragment-inside-a-viewpager/中有很多反馈但我在使这些解决方案发挥作用时遇到了一些麻烦。

我认为我创建界面的方式可能有问题，我在使其可从 ViewPager 调用时遇到了一些麻烦 SearchActivity.newInstance(new MyListener {...} )

我现在已经达到了我所得到的地步

java.lang.NullPointerException: Attempt to invoke virtual method 'android.support.v4.app.FragmentTransaction android.support.v4.app.FragmentManager.beginTransaction()' on a null object reference at com.example.ashaneen.firebaseapp.adapters.MainScreenAdapter$1.onFragmentChange(MainScreenAdapter.java:44) at com.example.ashaneen.firebaseapp.fragments.SearchFragment$4.onComplete(SearchFragment.java:132)

MainScreenAdapter.class

public class MainScreenAdapter extends FragmentPagerAdapter implements SearchFragment.MyListener {

    private static final String TAG = "MainScreenAdapter";

    private FragmentManager fragmentManager;
    private Fragment fragment1;


    public MainScreenAdapter(FragmentManager fm) {
        super(fm);
    }



    @Override
    public Fragment getItem(int position)
    {
        switch (position)
        {
            case 0:
                if (fragment1 == null)
                {
                    fragment1 = SearchFragment.newInstance(new SearchFragment.MyListener() {
                        @Override
                        public void onFragmentChange() {
                            fragmentManager.beginTransaction().remove(fragment1).commit();
                            fragment1 = ChatFragment.newInstance();
                            notifyDataSetChanged();
                        }
                    });
                }
                return fragment1;
            case 1:
                return new FriendsFragment();
            default:
                return new ChatFragment();
        }
    }

    @Override
    public int getItemPosition(@NonNull Object object) {
        return POSITION_NONE;
    }
    @Override
    public void onFragmentChange() {

    }

SearchFragment.class

 public class SearchFragment extends android.support.v4.app.Fragment  {

        public SearchFragment() {
        }

        private String TAG = "Profile2Fragment";

        public interface MyListener
        {
             void onFragmentChange();
        }

        static MyListener myListener = new MyListener() {
            public void onFragmentChange() {

            }
        };

    public static SearchFragment newInstance(MyListener myListener) {

       SearchFragment.myListener = myListener;
       return new SearchFragment();
    }
public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
        View view = inflater.inflate(R.layout.fragment_search, container, false);

        button = view.findViewById(R.id.btn_search);
        waitingRoomReference = db.collection("awaiting_room");




        button.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) 

{
                    myListener.onFragmentChange();
                }
            }
        });

                return view;
            }

Answer 1

尝试改变这个

public MainScreenAdapter(FragmentManager fm) {
    super(fm);
}

到

public MainScreenAdapter(FragmentManager fm) {
    super(fm);
    fragmentManager = fm;
}