TabLayout+ViewPager+Fragment, 为什么Fragment不走onHiddenChanged方法

Question

TabLayout+ViewPager+Fragment, 为什么Fragment不走onHiddenChanged方法

Answer 1

因为Fragment都是被销毁后新建的，不是原来的

Answer 2

先设置viewpager的setOffscreenPageLimit为fragment的总数，防止fragment销毁，其次，切换fragment会调用setUserVisibleHint方法，而不是onHiddenChanged。具体看FragmentPagerAdapter中的代码，参考public abstract class FragmentPagerAdapter extends PagerAdapter {
        ……
        public Object instantiateItem(ViewGroup container, int position) {
        if(this.mCurTransaction == null) {
            this.mCurTransaction = this.mFragmentManager.beginTransaction();
        }        long itemId = this.getItemId(position);
        String name = makeFragmentName(container.getId(), itemId);
        Fragment fragment = this.mFragmentManager.findFragmentByTag(name);
        if(fragment != null) {
            this.mCurTransaction.attach(fragment);
        } else {
            fragment = this.getItem(position);
            this.mCurTransaction.add(container.getId(), fragment, makeFragmentName(container.getId(), itemId));
        }        if(fragment != this.mCurrentPrimaryItem) {
            fragment.setMenuVisibility(false);
            fragment.setUserVisibleHint(false);
        }        return fragment;
    }    public void destroyItem(ViewGroup container, int position, Object object) {
        if(this.mCurTransaction == null) {
            this.mCurTransaction = this.mFragmentManager.beginTransaction();
        }        this.mCurTransaction.detach((Fragment)object);
    }    public void setPrimaryItem(ViewGroup container, int position, Object object) {
        Fragment fragment = (Fragment)object;
        if(fragment != this.mCurrentPrimaryItem) {
            if(this.mCurrentPrimaryItem != null) {
                this.mCurrentPrimaryItem.setMenuVisibility(false);
                this.mCurrentPrimaryItem.setUserVisibleHint(false);
            }            if(fragment != null) {
                fragment.setMenuVisibility(true);
                fragment.setUserVisibleHint(true);
            }            this.mCurrentPrimaryItem = fragment;
        }
    }
}

Answer 3

只有FragmentTransaction的show（）和hide（）方法才会调用onHiddenChanged（）方法

Answer 4

getUserVisibleHint获得当前是否可见