android - 保留 viewpager fragment android 的状态

Question

我在一个 fragment 中有一个 viewpager，我在其中显示了 3 个 fragment ，但是当我第一次打开该 fragment 时，它打开得很好，当我移动到另一个 fragment 并返回到 viewpager fragment 时，它没有显示 fragment 查看寻呼机然后我必须改变手机的方向或继续滑动 viewpager 以显示隐藏的 fragment 。

我用谷歌搜索了一下，现在我知道我必须为每个 fragment 设置标签并使用 findfragmentbytag 方法检索 fragment ，但问题是当我尝试将标签设置为 fragment 时

getSupportFragmentManager().beginTransaction().add(myFragment, "Some Tag").commit();

上面一行使我的应用程序崩溃并且 logcat 显示“无法将标签设置为 fragment ”，我知道我犯了一些愚蠢的错误

这是我的 fragment 的完整代码。如果有人能指导我在哪里编写设置 fragment 标签的代码，我将不胜感激。提前致谢。

public class MatchesListingFragment extends Fragment implements ActionBar.TabListener {

    Context context;
    SectionsPagerAdapter mSectionsPagerAdapter;
    ViewPager mViewPager;
    ActionBar actionBar;
    Matchlistings db;
    Bundle savedInstanceState;

    Fragment livescore,fixture,results;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        // TODO Auto-generated method stub
        super.onCreate(savedInstanceState);

        this.savedInstanceState = savedInstanceState;
        db = new Matchlistings(getActivity());
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
        Bundle savedInstanceState) {
        return inflater.inflate(R.layout.fragment_matches, container, false);
    }

    @Override
    public void onActivityCreated(Bundle savedInstanceState) {
        super.onActivityCreated(savedInstanceState);
        context = getActivity().getApplicationContext();

        if(savedInstanceState == null){
            livescore = new LiveScoreListingFragment();
            fixture = new FixturesListingFragment();
            results = new ResultsListingFragment();
        }

        if(!Constants.is_listing_refreshed){
            Log.i(MainActivity.TAG,"refreshing list");
            db.loadListingsFromServer().executeOnExecutor(AsyncTask.THREAD_POOL_EXECUTOR);
        }

        actionBar = getActivity().getActionBar();
        actionBar.setNavigationMode(ActionBar.NAVIGATION_MODE_TABS);

        if(mSectionsPagerAdapter == null)
        mSectionsPagerAdapter = new SectionsPagerAdapter(getActivity().getSupportFragmentManager());
        mViewPager = (ViewPager) getView().findViewById(R.id.pager);
        mViewPager.setAdapter(mSectionsPagerAdapter);

        mViewPager.setOnPageChangeListener(new ViewPager.SimpleOnPageChangeListener() {
            @Override
            public void onPageSelected(int position) {
                actionBar.setSelectedNavigationItem(position);
            }
        });


        for (int i = 0; i < mSectionsPagerAdapter.getCount(); i++) {
            Tab tb = actionBar.newTab()
            .setText(mSectionsPagerAdapter.getPageTitle(i))
            .setTabListener(this);

            actionBar.addTab(tb);

        }
    }

    public class SectionsPagerAdapter extends FragmentPagerAdapter {
        Fragment fragment;

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

        @Override
        public Fragment getItem(int position) {
            switch(position){
            case 0:

                fragment = livescore;
                return fragment;
            case 1:
                fragment = fixture;
                return fragment;
            case 2:
                fragment = results;
                return fragment;
            case 3:
                fragment = new LiveScoreListingFragment();
                return fragment;
            }
            return null;
        }

        @Override
        public int getCount() {
            return 4;
        }

        @Override
        public CharSequence getPageTitle(int position) {
            switch (position) {
            case 0:
                return "LIVE";
            case 1:
                return "FIXTURES";
            case 2:
                return "RESULTS";
            case 3:
                return "HOT";
            }
            return null;
        }
    }

    @Override
    public void onDestroy() {
        // TODO Auto-generated method stub
        super.onDestroy();
        actionBar.removeAllTabs();
        actionBar.setNavigationMode(ActionBar.NAVIGATION_MODE_STANDARD);
    }

    @Override
    public void onTabReselected(Tab arg0, FragmentTransaction arg1) {
        // TODO Auto-generated method stub

    }

    @Override
    public void onTabSelected(Tab arg0, FragmentTransaction arg1) {
        // TODO Auto-generated method stub

    }

    @Override
    public void onTabUnselected(Tab arg0, FragmentTransaction arg1) {
        // TODO Auto-generated method stub

    }

}

编辑:我现在尝试通过标签从 viewpager 获取 fragment ，而不是每次都创建新 fragment 。但问题还是一样。

FixturesListingFragment fixture = (FixturesListingFragment) getActivity().getSupportFragmentManager().findFragmentByTag("android:switcher:"+R.id.pager+":1");
                if(fixture == null)
                    fixture = new FixturesListingFragment();

Answer 1

您是否尝试过使用setOffscreenPageLimit？如果您有 3 个页面，则将其设置为 2。这样即使应用程序处于空闲状态，也不会重新创建页面。这是 link