viewapger+tablayout的自动化工具类MyTabL

说明

之所以又用回viewpager+tablayout是因为有一个需求 这个东西出现了bug
当修改viewpager2的宽度变化会导致fragment显示不正常，重叠，位置不对，宽度不对等各种问题。
这是我提的问题
https://github.com/android/views-widgets-samples/issues/234
牛逼的你觉得没问题的可以指导一下

viewapger+tablayout的自动化工具类MyTabLayoutMediator，参照viewpager2+tablayout 拷贝的TabLayoutMediator轮子.

实现原理

实现原理很简单，从viewpager2的逻辑可以看出来autoRefresh是根据registerAdapterDataObserver实现的，
viewpager 就改成registerDataObserver
自动生成tab标题的回调还是使用TabLayoutMediator.TabConfigurationStrategy避免创建无意义的类。

用法和TabLayoutMediator一样

用法

  myTabLayoutMediator = new MyTabLayoutMediator(getBinding().tabLayout, getBinding().viewpager2, true, new TabLayoutMediator.TabConfigurationStrategy() {
                    @Override
                    public void onConfigureTab(@NonNull TabLayout.Tab tab, int position) {

                        tab.setText(data.get(position).first.getTitle());
                    }

                });
                myTabLayoutMediator.attach();

完整源码

import static androidx.viewpager2.widget.ViewPager2.SCROLL_STATE_DRAGGING;
import static androidx.viewpager2.widget.ViewPager2.SCROLL_STATE_IDLE;
import static androidx.viewpager2.widget.ViewPager2.SCROLL_STATE_SETTLING;

import android.database.DataSetObserver;

import androidx.annotation.NonNull;
import androidx.viewpager.widget.PagerAdapter;
import androidx.viewpager.widget.ViewPager;

import com.google.android.material.tabs.TabLayout;
import com.google.android.material.tabs.TabLayoutMediator;

import java.lang.ref.WeakReference;

/**
 * Author:Lozn
 * Email:qssq521@gmail.com
 * 2021/12/3
 * 15:58
 */
public class MyTabLayoutMediator {

    private final TabLayout tabLayout;
    private final ViewPager viewPager;
    private final boolean autoRefresh;
    private final TabLayoutMediator.TabConfigurationStrategy tabConfigurationStrategy;
    private final boolean smoothScroll;
    private boolean attached;
    private ViewPagerOnTabSelectedListener onTabSelectedListener;
    private PagerAdapter adapter;
    private PagerAdapterObserver pagerAdapterObserver;
    private TabLayoutOnPageChangeCallback onPageChangeCallback;

    public MyTabLayoutMediator(
            @NonNull TabLayout tabLayout,
            @NonNull ViewPager viewPager,
            @NonNull TabLayoutMediator.TabConfigurationStrategy tabConfigurationStrategy) {
        this(tabLayout, viewPager, /* autoRefresh= */ true, tabConfigurationStrategy);
    }

    public MyTabLayoutMediator(
            @NonNull TabLayout tabLayout,
            @NonNull ViewPager viewPager,
            boolean autoRefresh,
            @NonNull TabLayoutMediator.TabConfigurationStrategy tabConfigurationStrategy) {
        this(tabLayout, viewPager, autoRefresh, /* smoothScroll= */ true, tabConfigurationStrategy);
    }
    public MyTabLayoutMediator(TabLayout tabLayout, ViewPager viewpager2, boolean autoRefresh, boolean smoothScroll,TabLayoutMediator.TabConfigurationStrategy tabConfigurationStrategy) {
        this.tabLayout = tabLayout;
        this.viewPager = viewpager2;
        this.smoothScroll=smoothScroll;
        this.autoRefresh = autoRefresh;
        this.tabConfigurationStrategy = tabConfigurationStrategy;
    }
    public MyTabLayoutMediator attach() {
        if (attached) {
            throw new IllegalStateException("TabLayoutMediator is already attached");
        }
        adapter = viewPager.getAdapter();
        if (adapter == null) {
            throw new IllegalStateException(
                    "TabLayoutMediator attached before ViewPager has an " + "adapter");
        }
        attached = true;
        // Add our custom OnPageChangeCallback to the ViewPager
       /* viewPager.addOnLayoutChangeListener(new View.OnLayoutChangeListener() {
            @Override
            public void onLayoutChange(View v, int left, int top, int right, int bottom, int oldLeft, int oldTop, int oldRight, int oldBottom) {
                viewPager.removeOnLayoutChangeListener(this);
                populateTabsFromPagerAdapter();

            }
        });*/
        onPageChangeCallback = new TabLayoutOnPageChangeCallback(tabLayout);
        viewPager.addOnPageChangeListener(onPageChangeCallback);
        // Now we'll add a tab selected listener to set ViewPager's current item
        onTabSelectedListener = new MyTabLayoutMediator.ViewPagerOnTabSelectedListener(viewPager, smoothScroll);
        tabLayout.addOnTabSelectedListener(onTabSelectedListener);
        // Now we'll populate ourselves from the pager adapter, adding an observer if
        // autoRefresh is enabled
        if (autoRefresh) {
            // Register our observer on the new adapter
//            pagerAdapterObserver = new TabLayoutMediator.PagerAdapterObserver();
//            adapter.registerAdapterDataObserver(pagerAdapterObserver);
            pagerAdapterObserver = new PagerAdapterObserver();
            adapter.registerDataSetObserver(pagerAdapterObserver);
        }
        populateTabsFromPagerAdapter();
        // Now update the scroll position to match the ViewPager's current item
        tabLayout.setScrollPosition(viewPager.getCurrentItem(), 0f, true);
        return this;
    }

    public void detach() {
        if (autoRefresh && adapter != null) {
            adapter.unregisterDataSetObserver(pagerAdapterObserver);
            pagerAdapterObserver = null;
        }
        tabLayout.removeOnTabSelectedListener(onTabSelectedListener);
        viewPager.removeOnPageChangeListener(onPageChangeCallback);
        onTabSelectedListener = null;
        onPageChangeCallback = null;
        adapter = null;
        attached = false;
    }
    public boolean isAttached() {
        return attached;
    }

    @SuppressWarnings("WeakerAccess")
    void populateTabsFromPagerAdapter() {
        tabLayout.removeAllTabs();
        if (adapter != null) {
            int adapterCount = adapter.getCount();
            for (int i = 0; i < adapterCount; i++) {
                TabLayout.Tab tab = tabLayout.newTab();
                tabConfigurationStrategy.onConfigureTab(tab, i);
                tabLayout.addTab(tab, false);
            }
            // Make sure we reflect the currently set ViewPager item
            if (adapterCount > 0) {
                int lastItem = tabLayout.getTabCount() - 1;
                int currItem = Math.min(viewPager.getCurrentItem(), lastItem);
                if (currItem != tabLayout.getSelectedTabPosition()) {
                    tabLayout.selectTab(tabLayout.getTabAt(currItem));
                }
            }
        }
    }
    private static class TabLayoutOnPageChangeCallback implements ViewPager.OnPageChangeListener {
        @NonNull private final WeakReference<TabLayout> tabLayoutRef;
        private int previousScrollState;
        private int scrollState;

        TabLayoutOnPageChangeCallback(TabLayout tabLayout) {
            tabLayoutRef = new WeakReference<>(tabLayout);
            reset();
        }

        @Override
        public void onPageScrollStateChanged(final int state) {
            previousScrollState = scrollState;
            scrollState = state;
        }

        @Override
        public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {
            TabLayout tabLayout = tabLayoutRef.get();
            if (tabLayout != null) {
                // Only update the text selection if we're not settling, or we are settling after
                // being dragged
                boolean updateText =
                        scrollState != SCROLL_STATE_SETTLING || previousScrollState == SCROLL_STATE_DRAGGING;
                // Update the indicator if we're not settling after being idle. This is caused
                // from a setCurrentItem() call and will be handled by an animation from
                // onPageSelected() instead.
                boolean updateIndicator =
                        !(scrollState == SCROLL_STATE_SETTLING && previousScrollState == SCROLL_STATE_IDLE);
                tabLayout.setScrollPosition(position, positionOffset, updateText, updateIndicator);
            }
        }

        @Override
        public void onPageSelected(final int position) {
            TabLayout tabLayout = tabLayoutRef.get();
            if (tabLayout != null
                    && tabLayout.getSelectedTabPosition() != position
                    && position < tabLayout.getTabCount()) {
                // Select the tab, only updating the indicator if we're not being dragged/settled
                // (since onPageScrolled will handle that).
                boolean updateIndicator =
                        scrollState == SCROLL_STATE_IDLE
                                || (scrollState == SCROLL_STATE_SETTLING
                                && previousScrollState == SCROLL_STATE_IDLE);
                tabLayout.selectTab(tabLayout.getTabAt(position), updateIndicator);
            }
        }

        void reset() {
            previousScrollState = scrollState = SCROLL_STATE_IDLE;
        }
    }




    /**
     * A {@link TabLayout.OnTabSelectedListener} class which contains the necessary calls back to the
     * provided {@link ViewPager2} so that the tab position is kept in sync.
     */
    public static class ViewPagerOnTabSelectedListener implements TabLayout.OnTabSelectedListener {
        private final ViewPager viewPager;
        private final boolean smoothScroll;

        ViewPagerOnTabSelectedListener(ViewPager viewPager, boolean smoothScroll) {
            this.viewPager = viewPager;
            this.smoothScroll = smoothScroll;
        }

        @Override
        public void onTabSelected(@NonNull TabLayout.Tab tab) {
            viewPager.setCurrentItem(tab.getPosition(), smoothScroll);
        }

        @Override
        public void onTabUnselected(TabLayout.Tab tab) {
            // No-op
        }

        @Override
        public void onTabReselected(TabLayout.Tab tab) {
            // No-op
        }
    }

    private class PagerAdapterObserver extends DataSetObserver{
        PagerAdapterObserver() {}

        @Override
        public void onChanged() {
            populateTabsFromPagerAdapter();
        }
/*
        @Override
        public void onItemRangeChanged(int positionStart, int itemCount) {
            populateTabsFromPagerAdapter();
        }

        @Override
        public void onItemRangeChanged(int positionStart, int itemCount, @Nullable Object payload) {
            populateTabsFromPagerAdapter();
        }

        @Override
        public void onItemRangeInserted(int positionStart, int itemCount) {
            populateTabsFromPagerAdapter();
        }

        @Override
        public void onItemRangeRemoved(int positionStart, int itemCount) {
            populateTabsFromPagerAdapter();
        }

        @Override
        public void onItemRangeMoved(int fromPosition, int toPosition, int itemCount) {
            populateTabsFromPagerAdapter();
        }*/
    }
}