TabLayout中的片段僅在用戶滑動Android時加載

Question

嗨我正在使用tablayout和viewpager制作一個帶有A fragment的應用程序，里面有很少的子fragment 。 問題是我的所有子fragment （來自Tablayout ）總是執行（每當用戶單擊父fragment時加載所有代碼。如何只在用戶滑動它時加載子fragment （例如我有2個選項卡，內容）在標簽2中僅在用戶滑動到標簽2時加載

這是我的父fragment代碼

public class ManageEventFragment extends Fragment {


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


    TabLayout tabLayout;
    ViewPager viewPager;

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        View viewFragment = inflater.inflate(R.layout.fragment_manage_event, container, false);

        viewPager = (ViewPager) viewFragment.findViewById(R.id.viewPager);

        tabLayout = (TabLayout) viewFragment.findViewById(R.id.tabLayout);

        viewPager.setAdapter(new CustomAdapter(getChildFragmentManager(), getContext()));
        viewPager.addOnPageChangeListener(new TabLayout.TabLayoutOnPageChangeListener(tabLayout));

        return viewFragment;
    }

    @Override
    public void onActivityCreated(Bundle savedInstanceState) {

        //        tabLayout.setupWithViewPager(viewPager);
        tabLayout.post(new Runnable() {
            @Override
            public void run() {
                tabLayout.setupWithViewPager(viewPager);
            }
        });

        tabLayout.setOnTabSelectedListener(new TabLayout.OnTabSelectedListener() {
            @Override
            public void onTabSelected(TabLayout.Tab tab) {
                viewPager.setCurrentItem(tab.getPosition());
            }

            @Override
            public void onTabUnselected(TabLayout.Tab tab) {
                viewPager.setCurrentItem(tab.getPosition());
            }

            @Override
            public void onTabReselected(TabLayout.Tab tab) {
                viewPager.setCurrentItem(tab.getPosition());
            }
        });

        if (ViewCompat.isLaidOut(tabLayout)) {
            tabLayout.setupWithViewPager(viewPager);
        } else {
            tabLayout.addOnLayoutChangeListener(new View.OnLayoutChangeListener() {
                @Override
                public void onLayoutChange(View v, int left, int top, int right, int bottom, int oldLeft, int oldTop, int oldRight, int oldBottom) {
                    tabLayout.setupWithViewPager(viewPager);
                    tabLayout.removeOnLayoutChangeListener(this);
                }
            });
        }

        super.onActivityCreated(savedInstanceState);

    }


    //TabLayout and ViewPager class
    private class CustomAdapter extends FragmentPagerAdapter {

        private String fragments[] = {"Edit Event", "Create Event"};

        public CustomAdapter(FragmentManager fragmentManager, Context context) {
            super(fragmentManager);
        }

        @Override
        public Fragment getItem(int position) {
            switch (position) {
                case 0:
                    return new EditEventFragment();
                case 1:
                    return new CreateEventFragment();
                default:
                    return null;
            }
        }

        @Override
        public int getCount() {
            return fragments.length;
        }

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

    }

}

而我的孩子片段代碼。 我希望這些代碼只在用戶滑動到子選項卡時執行。 任何幫助都非常感謝，謝謝

@Override
    public void onActivityCreated(Bundle savedInstanceState) {
        super.onActivityCreated(savedInstanceState);

        //Initializing our listEvents list
        listEvents = new ArrayList();

        recyclerView.setHasFixedSize(true);
        layoutManager = new LinearLayoutManager(getContext());
        recyclerView.setLayoutManager(layoutManager);

        adapter = new EventAdapterEdit(getContext(),listEvents);
        recyclerView.setAdapter(adapter);


        requestQueue = Volley.newRequestQueue(getContext());

        adapter = new EventAdapterEdit(getContext(),listEvents);
        recyclerView.setAdapter(adapter);

        getEventDetailRespond(requestQueue);

Answer 1

@Override public void setUserVisibleHint(boolean isVisibleToUser) {
    super.setUserVisibleHint(isVisibleToUser);
}

您可以在ViewPager Adapter片段中使用上述方法

if(isVisibleToUser){//dosomething when the fragment is visible}
else{//dosomething else.}

要注意不要在那里或其他任何地方初始化視圖，在onViewCreated初始化你的視圖並調用你想在setUserVisibleHint執行的方法。 另一個丑陋的方法是向ViewPager添加一個滾動偵聽ViewPager並獲取當前項目位置並觸發片段內的操作。 要從ViewPager Adapter獲取片段，您可以這樣做：

 MyFragment frag = (MyFragment) pager.getAdapter().instantiateItem(pager, position);

然后你可以調用MyFragment的方法

Answer 2

Viewpager默認加載相鄰的片段以確保使應用程序流暢，以便當用戶滑動到片段（已經加載）時，它就在那里。 要更改是默認行為，請使用viewpager.setOffscreenPageLimit(int limit) ，其中limit是預先加載的那個片段旁邊的片段數。 希望這可以幫助