Fix glitches on setting up TabLayout with ViewPager

gistfile1.java

package io.github.no99gk.play;

import android.support.design.widget.TabLayout;
import android.support.v4.view.PagerAdapter;
import android.support.v4.view.ViewPager;

import java.lang.ref.Reference;
import java.lang.ref.WeakReference;

/** Helper class which fixes some glitches on TabLayout */
public class TabLayoutHelper {
    public static void setupWithViewPager(TabLayout tabLayout, ViewPager viewPager) {
        PagerAdapter adapter = viewPager.getAdapter();
        if (adapter == null) {
            throw new IllegalArgumentException("ViewPager does not have a PagerAdapter set");
        }

        tabLayout.setTabsFromPagerAdapter(adapter);
        ViewPagerBinder.bind(tabLayout, viewPager);
    }

    private static class ViewPagerBinder
            implements TabLayout.OnTabSelectedListener, ViewPager.OnPageChangeListener {
        private final Reference<TabLayout> tabLayoutRef;
        private final Reference<ViewPager> viewPagerRef;
        private int scrollState;
        private boolean autoScrolling;
        private boolean pendingTabSelection;

        private ViewPagerBinder(TabLayout tabLayout, ViewPager viewPager) {
            tabLayoutRef = new WeakReference<>(tabLayout);
            viewPagerRef = new WeakReference<>(viewPager);
        }

        static ViewPagerBinder bind(TabLayout tabLayout, ViewPager viewPager) {
            ViewPagerBinder binder = new ViewPagerBinder(tabLayout, viewPager);
            viewPager.addOnPageChangeListener(binder);
            tabLayout.setOnTabSelectedListener(binder);
            return binder;
        }

        @Override
        public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {
            TabLayout tabLayout = tabLayoutRef.get();
            if (tabLayout != null && !autoScrolling) {
                tabLayout.setScrollPosition(position, positionOffset,
                        scrollState == ViewPager.SCROLL_STATE_DRAGGING
                                || (scrollState == ViewPager.SCROLL_STATE_SETTLING
                                        && (positionOffset == 0f || positionOffset == 1f)));
            }
        }

        @Override
        public void onPageSelected(int position) {
            selectTab(position);
        }

        private void selectTab(int position) {
            TabLayout tabLayout = this.tabLayoutRef.get();
            if (tabLayout != null) {
                tabLayout.getTabAt(position).select();
            }
        }

        private void syncTab() {
            ViewPager viewPager = viewPagerRef.get();
            if (viewPager != null) {
                selectTab(viewPager.getCurrentItem());
            }
        }

        @Override
        public void onPageScrollStateChanged(int state) {
            switch (state) {
                case ViewPager.SCROLL_STATE_SETTLING:
                    if (scrollState == ViewPager.SCROLL_STATE_IDLE) {
                        autoScrolling = true;
                    }
                    break;
                case ViewPager.SCROLL_STATE_IDLE:
                    if (pendingTabSelection) syncTab();

                    autoScrolling = false;
                    pendingTabSelection = false;
                    break;
            }
            scrollState = state;
        }

        @Override
        public void onTabSelected(TabLayout.Tab tab) {
            ViewPager viewPager = viewPagerRef.get();
            if (viewPager != null) {
                if (scrollState == ViewPager.SCROLL_STATE_SETTLING) {
                    pendingTabSelection = true;
                } else {
                    viewPager.setCurrentItem(tab.getPosition());
                }
            }
        }

        @Override public void onTabUnselected(TabLayout.Tab tab) {}
        @Override public void onTabReselected(TabLayout.Tab tab) {}
    }
}