android - FragmentStatePagerAdapter 重复 fragment

Question

我在我的单一 Activity 应用程序上使用嵌套的 FragmentStatePagerAdapter。当前布局是:

Activitiy
  - Login Fragment
  - Master Fragment
      - Tab Fragment #1
      - Tab Fragment #2
      - Tab Fragment #3
  - Another Fragment
  - Another Fragment

例如，每次我从“另一个 fragment ”切换回“主 fragment ”时，FragmentStatePagerAdapter 都会将同一个项目实例化两次

第一次:Tab fragment #1 #2 #3
第二次:Tab fragment #1 #1 #2 #2 #3 #3
第三次:Tab fragment #1 #1 #1 #2 #2 #2 #3 #3 #3。

我使用的是从 fragment 移动到 fragment

getSupportFragmentManager()
    .beginTransaction()
    .replace(android.R.id.content, XXXX.newInstance(query), TAG_XXX)
    .addToBackStack(null)
    .commit();

MasterFragment代码:

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

private void initFragmentAdapter() {
    final FragmentSimpleAdapter adapter = new FragmentSimpleAdapter(getChildFragmentManager());

    adapter.addFragment(
            getString(...),
            "...",
            XXX.class);
    ...

    ViewPager viewPager = (ViewPager) getActivity().findViewById(android.R.id.tabcontent);
    viewPager.setAdapter(adapter);
    viewPager.setOffscreenPageLimit(4);

    PagerSlidingTabStrip viewTabs = (PagerSlidingTabStrip) getActivity().findViewById(
            android.R.id.tabhost);
    viewTabs.setViewPager(viewPager);
    viewTabs.setOnPageChangeListener(adapter);
}
    private final class FragmentSimpleAdapter extends FragmentStatePagerAdapter
       implements ViewPager.OnPageChangeListener {
    private final List<String> mTitles = new LinkedList<>();
    private final List<String> mInstances = new LinkedList<>();
    private final List<String> mTag = new LinkedList<>();
    private Map<Integer, String> mFragmentTags;
    private FragmentManager mFragmentManager;

    public FragmentSimpleAdapter(FragmentManager fm) {
        super(fm);
        mFragmentManager = fm;
        mFragmentTags = new HashMap<>();
    }

    @Override
    public int getCount() {
        return mTitles.size();
    }

    @Override
    public CharSequence getPageTitle(int position) {
        return mTitles.get(position);
    }

    @Override
    public Fragment getItem(int position) {
        return Fragment.instantiate(getActivity(), mInstances.get(position), null);
    }

    @Override
    public Object instantiateItem(ViewGroup container, int position) {
        Object obj = super.instantiateItem(container, position);
        if (obj instanceof Fragment) {
            Fragment f = (Fragment) obj;
            String tag = f.getTag();
            mFragmentTags.put(position, tag);
        }
        return obj;
    }

    public Fragment getFragment(int position) {
        String tag = mFragmentTags.get(position);
        if (tag == null) {
            return null;
        }
        return mFragmentManager.findFragmentByTag(tag);
    }

    public FragmentSimpleAdapter addFragment(String title, String tag,
                                             Class<? extends Fragment> fragment) {
        mTitles.add(title);
        mTag.add(tag);
        mInstances.add(fragment.getName());
        return this;
    }

    @Override
    public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {
    }

    @Override
    public void onPageSelected(int position) {
            Analytics.sendViewAnalytic(mTag.get(position))
    }

    @Override
    public void onPageScrollStateChanged(int state) {
    }
}

Answer 1

问题:

PagerSlidingTabStrip viewTabs = (PagerSlidingTabStrip) getActivity().findViewById(
        android.R.id.tabhost);

每次返回 Master's Fragment 时，您都在尝试重新创建 PagerSlidingTabStrip，从而添加了不必要的 fragment 。

解决方法:

你需要先检查选项卡是否已经存在我真的不知道 PagerSlidingTabStrip 我认为这是一个定制类。