碎片从表3返回时消失。

Question

我有一个包含片段的ViewPager活动。当单击一个按钮时，第一个片段(Book)创建一个嵌套的片段(Singlebook)。问题是，当我从fragment3回来时，第一个片段及其组件就消失了。我认为这与onSaveState或onDestroy有关。

我已经尝试过重写onDestroy，并在父片段(Book)上使用了childFragmentManager，但是它没有添加到后台堆栈。

MainActivity.java :

public class MainActivity extends FragmentActivity {

ViewPager viewPager;
MyPagerAdapter adapter;
public FragmentManager fragmentManager = getSupportFragmentManager();

@Override
protected void onCreate(Bundle savedInstanceState) {

    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    TabLayout tabLayout = (TabLayout) findViewById(R.id.tl_tabs);
    viewPager = (ViewPager) findViewById(R.id.vp_12);

    Fragment[] fragments = new Fragment[3];
    fragments[0] = new Book();
    fragments[1] = new Search();
    fragments[2] = new Study();
    adapter = new MyPagerAdapter(fragmentManager, fragments);
    viewPager.setAdapter(adapter);
    tabLayout.setupWithViewPager(viewPager);
}
}

class MyPagerAdapter extends FragmentStatePagerAdapter {

    private Fragment[] fragments;

    public MyPagerAdapter(FragmentManager fm, Fragment[] fragments) {
        super(fm);
        this.fragments = fragments;
    }

    @Override
    public Fragment getItem(int position) {
        switch (position) {
            case 0:
                return fragments[0];
            case 1:
                return fragments[1];
            case 2:
                return fragments[2];
            default:
                return fragments[0];
        }
    }

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

    @Override
    public CharSequence getPageTitle(int position) {

        switch (position) {
            case 0:
                return "단어장";
            case 1:
                return "단어 검색";
            case 2:
                return "내 정보";
            default:
                return "";
        }
    }
}

Book.java :

public class Book extends Fragment {

FragmentManager fragmentManager;
private Button btn;
private EditText editText;

public Book() {
    // Required empty public constructor
}
@Override
public View onCreateView( LayoutInflater inflater,  ViewGroup container,
                         Bundle savedInstanceState) {
    View view = inflater.inflate(R.layout.fragment_book, container, false);
    btn = (Button) view.findViewById(R.id.btn_toQuiz);
    editText =(EditText) view.findViewById(R.id.edit_text);
    ViewPager viewPager = (ViewPager) container;

    btn.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            fragmentManager = getChildFragmentManager();

            fragmentManager.beginTransaction()
                    .add(R.id.fl_BookContainer,new singleBook(),"TAG")
                    .addToBackStack(null)
                    .commit();

        }
    });
    return view;
}

}

Answer 1

viewPager = (ViewPager) findViewById(R.id.vp_12);


adapter = new MyPagerAdapter(fragmentManager, fragments);
    viewPager.setAdapter(adapter);
    tabLayout.setupWithViewPager(viewPager);

至

viewPager = (ViewPager) findViewById(R.id.vp_12);
viewPager.setOffscreenPageLimit(3);

adapter = new MyPagerAdapter(getChildFragmentManager(), fragments);
    viewPager.setAdapter(adapter);
    tabLayout.setupWithViewPager(viewPager);

Answer 2

默认情况下，FragmentStatePagerAdapter只能创建两个片段，当您转到第三个片段时，它将删除第一个片段。因此，您需要调用setOffscreenPageLimit方法来保存所有片段，这些片段在将适配器设置为视图寻呼机时添加到寻呼机适配器中。

Fragment[] fragments = new Fragment[3];
fragments[0] = new Book();
fragments[1] = new Search();
fragments[2] = new Study();
adapter = new MyPagerAdapter(fragmentManager, fragments);
viewPager.setAdapter(adapter);
viewPager.setOffscreenPageLimit(fragments.size());
tabLayout.setupWithViewPager(viewPager);