一、页面初始化配置

private val mAdapter by lazy {
    MainViewPage2Adapter(this).apply {
        setFragmentListener {
        //子fragment回调数据给act或fragment
        }
    }
}
mViewPager2 = findViewById(R.id.mViewPager2)
//1、关闭预加载方法-->
//方法一：是否支持预取 isItemPrefetchEnabled
(mViewPager2?.getChildAt(0) as RecyclerView).layoutManager?.apply {
        isItemPrefetchEnabled = false
    }
//方法二：想要限制页面预加载
mViewPager2.offscreenPageLimit=
ViewPager2.OFFSCREEN_PAGE_LIMIT_DEFAULT
//2、设置数据  子条目bean 重写hashCode和equals
mAdapter.setNewData(fragmentList)
mViewPager2?.adapter = mAdapter
//3、tab vp 绑定  false即可去除切换动画
tabLayoutMediator = TabLayoutMediator(
        tabLayout!!, mViewPager2!!, true, false
    ) { tab, position ->
        tab.customView = getTabView(position)
    }
    tabLayoutMediator?.attach()
//4、是否开启离屏渲染，setup
    mViewPager2?.offscreenPageLimit = mAdapter.itemCount
//5、注册your mPageChangeCallback
    viewPager2.registerOnPageChangeCallback(mPageChangeCallback);
//6、切换到默认选择项,下一帧之后才有效
    viewPager2.post(() -> viewPager2.setCurrentItem(currSelectPos, false));

二、ViewPager2获取指定页面的fragment 比如首页

(supportFragmentManager.findFragmentByTag(mAdapter.fragmentTag(0)) as? HomeRecyclerListFragment)?.xxx

动态diff更新

diff New List

val array = ArrayList<TabEntity>()
      array.add(TabEntity("666", 0))
      array.add(TabEntity("888", 1))
      array.add(TabEntity("999", 2))
      mAdapter.mergeList(array) {//call
            showToast("success")
        }

add tabEntity

mAdapter.addFragment(tabEntity,pos) {
            //回调
            tv_add_text?.text = "add success"
        }

remove tabEntity

 mAdapter.removeFragment(tabEntity) {
            tv_add_text?.text = "del success"
        }

子类继承Use BaseDiffPagerAdapter

class MainViewPage2Adapter(fragmentActivity: FragmentActivity) :
BaseDiffPager2Adapter<TabEntity,Boolean>(fragmentActivity) {
override fun genDiffItemCall(): DiffUtil.ItemCallback<TabEntity> {
    return diffCallBack
}

override fun createFragment(position: Int): Fragment {
   //listener为回调
    return FragmentFactory.genFragment(position,listener)
}

companion object {
    val diffCallBack = object : DiffUtil.ItemCallback<TabEntity>() {
        override fun areItemsTheSame(oldItem: TabEntity, newItem: TabEntity): Boolean {
            return oldItem.hashCode() == newItem.hashCode()
        }

        override fun areContentsTheSame(oldItem: TabEntity, newItem: TabEntity): Boolean {
            return oldItem == newItem
        }

    }
}
}

定义接口能力

interface IViewPagerBasic<T,L> {
fun addFragment(addFragmentTab: T, insertPos: Int = -1, commitCallback: Runnable? = null) {
}
fun removeFragment(removeFragmentTab: T, commitCallback: Runnable? = null) {
}
fun removeFragment(pos: Int, commitCallback: Runnable? = null) {
}
fun genDiffItemCall(): DiffUtil.ItemCallback<T>
fun fragmentTag(pos: Int):String
fun setFragmentListener(l: ((L)->Unit)?=null){
}
 }

基类BaseDiffPagerAdapter

/**
 * 名称：支持 add  remove 的viewpager2 adapter,支持异步diff
 */
abstract class BaseDiffPager2Adapter<T, L> : FragmentStateAdapter, IViewPagerBasic<T, L> {
private var mDiffer: AsyncListDiffer<T>? = null
protected var listener: ((L) -> Unit)? = null

constructor(fragment: Fragment) : super(fragment)
constructor(fragmentActivity: FragmentActivity) : super(fragmentActivity)

init {
    mDiffer = AsyncListDiffer(this.getAdapter(), this.genDiffItemCall())
}

override fun setFragmentListener(l: ((L) -> Unit)?) {
    this.listener = l
}

override fun containsItem(itemId: Long): Boolean {
    mDiffer?.currentList?.forEach {
        if (it.hashCode().toLong() == itemId) {
            return true
        }
    }
    return false
}

override fun addFragment(addFragmentTab: T, insertPos: Int, commitCallback: Runnable?) {
    val arrayList = getMutablePageList()
    if (!arrayList.contains(addFragmentTab)) {
        val inPos = if (insertPos != -1 && insertPos <= itemCount) insertPos else itemCount
        arrayList.add(inPos, addFragmentTab)
        mergeList(arrayList, commitCallback)
    }

}

override fun removeFragment(removeFragmentTab: T, commitCallback: Runnable?) {
    removeFragmentTab?.let {
        val arrayList = getMutablePageList()
        val index = arrayList.indexOf(it)
        if (index != -1) {
            arrayList.remove(it)
            mergeList(arrayList, commitCallback)
        }
    }
}

override fun removeFragment(pos: Int, commitCallback: Runnable?) {
    val arrayList = getMutablePageList()
    if (pos < arrayList.size) {
        removeFragment(arrayList[pos], commitCallback)
    }

}

override fun getItemCount(): Int {
    return mDiffer?.currentList?.size ?: 0
}

fun setNewData(list: ArrayList<T>) {
    mergeList(list)
}

fun mergeList(mNewList: ArrayList<T>, commitCallback: Runnable? = null) {
    val arrayList = getMutablePageList()
    if (arrayList.containsAll(mNewList) && arrayList.size == mNewList.size) return
    mDiffer?.submitList(mNewList, commitCallback)
}

override fun getItemId(position: Int): Long {
    if ((mDiffer?.currentList?.size ?: 0) < position) {
        return 0L
    }
    return mDiffer!!.currentList[position].hashCode().toLong()
}


private fun getMutablePageList(): ArrayList<T> {
    return ArrayList(mDiffer?.currentList ?: ArrayList())
}

private fun getAdapter(): BaseDiffPager2Adapter<T, L> {
    return this
}

override fun fragmentTag(pos: Int): String {
    return "f" + getItemId(pos)
}
 } 

FragmentFactory

object FragmentFactory {
//pos 回调
fun genFragment(index: Int,call: ((Boolean)->Unit)?=null): Fragment {
    return when (index) {
        0 -> {
            HomeRecyclerListFragment.newInstance("1").apply {
                setOnScrollListener(call)
            }
        }
        1 -> { your fragment }
        else -> {
            TestListFragment.newInstance("99")
        }
    }
}

}