android - 如何在 viewpager 中重新创建 fragment

Question

我有一个带有 5 个选项卡的 viewpager，每个选项卡都是向用户显示不同数据的 fragment ，每个 fragment 本身都有 recycleview，当用户更改选项卡时我需要将更新的数据重新插入到 recyclerview 中，我需要更新 View

每次我滑动到一个选项卡时，都需要加载该选项卡中 fragment 的一个新实例，以便更新数据。

我试过了:

1- I used FragmentStatePagerAdapter (nothing happens)

2- I Override getItemPosition method to return PagerAdapter.POSITION_NONE; (nothing happens)

3- setOffscreenPageLimit(0) (Nothing happens)

4- refresh function inside each fragment to be called onTabSelected (gives nullPointerException)

每次用户更改选项卡时，我如何从头开始重新创建 fragment
我真的需要知道。

我已经在这个问题上苦苦挣扎了一周，没有任何进展。我感谢任何帮助，无论是提示、评论还是建议。

让我知道我应该发布什么代码，谢谢。

编辑:
我的代码:

主要 Activity :

public class Sefaresh_activity3 extends AppCompatActivity implements Serializable, Sefaresh3_interface {
    Context context;
    Toolbar mtoolbar;
    private List<Food> food_list = new ArrayList<>();

    MyPagerAdapter adapter;
    Custom_TabLayout mTabLayout;
    ViewPager mpager;
@Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_sefaresh_activity3);
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.JELLY_BEAN_MR1) {
            getWindow().getDecorView().setLayoutDirection(View.LAYOUT_DIRECTION_LTR);
        }

        context = this;
        sqlHelper = new SqlHelper(this);
setupTabs();

private void setupTabs() {
        mtoolbar = (Toolbar) findViewById(R.id.app_bar);
        setSupportActionBar(mtoolbar);

        SpannableString s = new SpannableString(getTitle());
        s.setSpan(new TypefaceSpan(this, "IRAN Sans Bold.ttf"), 0, s.length(),
                Spannable.SPAN_EXCLUSIVE_EXCLUSIVE);
        setTitle(s);

        try {
            getSupportActionBar().setHomeButtonEnabled(true);
            getSupportActionBar().setDisplayHomeAsUpEnabled(true);
        } catch (Exception e) {
            L.m("something is wrong in toolbar section");
        }

        adapter = new MyPagerAdapter(getSupportFragmentManager());

        mTabLayout = (Custom_TabLayout) findViewById(R.id.tab_layout);
        mpager = (ViewPager) findViewById(R.id.viewpager);
        mpager.setAdapter(adapter);

        mTabLayout.setTabsFromPagerAdapter(adapter);
        mTabLayout.setupWithViewPager(mpager);

        mpager.addOnPageChangeListener(new TabLayout.TabLayoutOnPageChangeListener(mTabLayout));
        mTabLayout.setOnTabSelectedListener(new TabLayout.OnTabSelectedListener() {
            @Override
            public void onTabSelected(TabLayout.Tab tab) {
                L.m("tab selected" + tab.getPosition());
                mpager.setCurrentItem(tab.getPosition());

//                    Sefaresh3_fragment all_fragment = (Sefaresh3_fragment) adapter.getFragment_all();
//                    sefaresh3_fragment.onRefresh();

//                    Sefaresh3_fragment sefaresh3_fragment = (Sefaresh3_fragment) adapter.fragment_all;
//                    adapter.notifyDataSetChanged();

            }

            @Override
            public void onTabUnselected(TabLayout.Tab tab) {

            }

            @Override
            public void onTabReselected(TabLayout.Tab tab) {

            }
        });

    }

class MyPagerAdapter extends FragmentStatePagerAdapter {
       // public ArrayList<Fragment> fragmentArrayList = new ArrayList<>();
        Fragment fragment_all;
        Fragment fragment_pizza;
        Fragment fragment_sandwich;
        Fragment fragment_salad;
        Fragment fragment_coca;

        public Fragment getFragment_coca() {
            return fragment_coca;
        }

        public Fragment getFragment_all() {
            return fragment_all;
        }

        public Fragment getFragment_pizza() {
            return fragment_pizza;
        }

        public Fragment getFragment_sandwich() {
            return fragment_sandwich;
        }

        public Fragment getFragment_salad() {
            return fragment_salad;
        }

        String[] tabs = {
                "products",
                "new products",
                "featured",
                "star",
                "star2"
        };

        @Override
        public int getItemPosition(Object object) {
            return PagerAdapter.POSITION_NONE;
        }

        public MyPagerAdapter(FragmentManager fm) {
            super(fm);
            tabs = getResources().getStringArray(R.array.sefaresh3_tabs);
        }

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

        @Override
        public Fragment getItem(int num) {
            Fragment fragment = null;
            orders = new Orders();
            orders.setOrders(all_orders);
            switch (num) {
                case 0:
//                    fragment_all = Sefaresh3_fragment.newInstance("all", "");
//                    return new Sefaresh3_fragment().newInstance("all","");
                    return Sefaresh3_fragment.newInstance("all","");
                case 1:
                    fragment_pizza = Sefaresh3_fragment.newInstance("pizza", "");
                    return fragment_pizza;
                case 2:
                    fragment_sandwich = Sefaresh3_fragment.newInstance("sandwich", "");
                    return fragment_sandwich;
                case 3:
                    fragment_salad = Sefaresh3_fragment.newInstance("salad", "");
                    return fragment_salad;
                case 4:
                    fragment_coca = Sefaresh3_fragment.newInstance("coca", "");
                    return fragment_coca;
                default:
                    return fragment;
            }
        }

        @Override
        public CharSequence getPageTitle(int position) {
            return tabs[position];
        }

        @Override
        public int getCount() {
            return 5;
        }

    }

Answer 1

感谢大家的建议，经过一周的努力解决这个问题后，我找到了解决方案。

我尝试了几种方法，但最后我找到了解决方案。

我使用广播接收器告诉 fragment 更新列表，每次我需要更新 fragment 以更新数据列表时，我都会调用广播器。它很棒，而且效果很好

如果有人遇到同样的问题，我很乐意帮助他:) 谢谢。