ViewPager 内 Fragment 嵌套 ViewPager, setUserVisibleHint 方法不准确的问题的帮助类

NestedFragmentHelper.java

import android.support.v4.app.Fragment;
import android.support.v4.view.ViewPager;

/**
 * Created: chiemy
 * Date: 17/1/4
 * Description: 为解决 ViewPager 内 Fragment 嵌套 ViewPager, setUserVisibleHint 方法不准确的问题的帮助类
 */

public class NestedFragmentHelper implements ViewPager.OnPageChangeListener {
    private Fragment mFragment;
    private ViewPager mViewPager;
    private boolean mIsVisible;

    public NestedFragmentHelper(Fragment fragment) {
        mFragment = fragment;
        mIsVisible = fragment.getUserVisibleHint();
    }

    public void setupWithViewPager(ViewPager viewPager) {
        mViewPager = viewPager;
        mViewPager.addOnPageChangeListener(this);
    }

    public void setUserVisibleHint(boolean isVisibleToUser) {
        mIsVisible = isVisibleToUser;
        if (isVisibleToUser) {
            currentChildFragmentVisible();
        } else {
            allChildBecomeInvisible();
        }
    }

    private void allChildBecomeInvisible() {
        if (mViewPager == null) {
            return;
        }
        int size = mViewPager.getAdapter().getCount();
        for (int i = 0; i < size; i++) {
            fragmentVisibleChange(false, i);
        }
    }

    private void currentChildFragmentVisible() {
        if (mViewPager == null) {
            return;
        }
        fragmentVisibleChange(true, mViewPager.getCurrentItem());
    }

    private void fragmentVisibleChange(boolean isVisibleToUser, int index) {
        if (mViewPager == null) {
            return;
        }
        Fragment nestedFragment = mFragment.getChildFragmentManager().findFragmentByTag(makeFragmentName(mViewPager.getId(), index));
        if (nestedFragment instanceof NestedFragment) {
            ((NestedFragment) nestedFragment).setUserVisible(isVisibleToUser);
        }
    }

    private static String makeFragmentName(int viewPagerId, int index) {
        return "android:switcher:" + viewPagerId + ":" + index;
    }

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

    @Override
    public void onPageSelected(int position) {
        if (!mIsVisible) {
            return;
        }
        int size = mViewPager.getAdapter().getCount();
        for (int i = 0; i < size; i++) {
            fragmentVisibleChange(position == i, i);
        }
    }

    @Override
    public void onPageScrollStateChanged(int state) {
    }

    public interface NestedFragment {
        void setUserVisible(boolean visible);
    }
}