Android getParentFragment()在Fragment中的ViewPager中返回null

Question

我有一个Activity包含Fragmenta ViewPager.然后我Fragment在ViewPager中调用a的方法.但是如果那个Fragment然后调用getParentFragment(),它返回null.

为什么是getParentFragment()null？

---

包含ViewPager的主要片段:

public class MyFragment extends Fragment {
    private TabLayout mTabLayout;
    private ViewPager mViewPager;
    private ViewPagerAdapter mAdapter;

    @Override
    public void onActivityCreated(@Nullable Bundle savedInstanceState) {
        super.onActivityCreated(savedInstanceState);
        View view = getView();

        // Setup the ViewPager
        mViewPager = (ViewPager) view.findViewById(R.id.container);

        ViewPagerAdapter adapter = new ViewPagerAdapter(getChildFragmentManager(), getActivity());
        mViewPager.setAdapter(adapter);
        //setupViewPager(mViewPager);

        // Setup the TabLayout
        mTabLayout = (TabLayout) view.findViewById(R.id.tabs);
        mTabLayout.setupWithViewPager(mViewPager);
    }

    // This method is called from Activity.
    public void callNestedFragment() {
        if (isDetached()) {
            return;
        }

        // This fragment cannot be null, because it doesn't crash here. (this is just a sample).
        ((Fragment0) mViewPager.getItem(0)).testMethod();
    }
}

嵌套片段(内部mViewPager):

public class Fragment0 extends Fragment {

    ...

    public void testMethod() {
        if (isDetached()) {
            return;
        }

        // Why is getParentFragment() null? This is the log: "Parent fragment: null"
        Log.i(TAG, "Parent fragment: " + getParentFragment());
        return;
    }
}

的ViewPagerAdapter:

public class ViewPagerAdapter extends FragmentPagerAdapter {
    private Context mContext;

    public ViewPagerAdapter(FragmentManager manager, Context context) {
        super(manager);
        mContext = context;
    }

    @Override
    public Fragment getItem(int position) {
        switch (position) {
            case 0:
                return new Fragment0();
            case 1:
                return new Fragment1();
            case 2:
                return new Fragment2();
            case 3:
                return new Fragment3();
            case 4:
                return new Fragment4();
        }

        return null;
    }

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

如果需要更多代码,请告诉我.谢谢你的帮助.

Answer 1

我找到了答案。如果isDetached()为真，并不意味着getParentFragment()不为空。

testMethod()因此，这是新代码，而不是之前的签入：

public void testMethod() {
    if (isDetached() && getParentFragment() != null) {
        return;
    }

    ...
}

onStart()我现在还在内的方法中再次调用相同的方法Fragment0，其中getParentFragment()不应为空。