TabLayoutMediator2 -- 实现TabLayout+RecyclerView的锚点定位

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背景

在ViewPager2发布之后,TabLayout加入了一个非常好用的中间类--TabLayoutMediator来实现TabLayout与ViewPager2的绑定与滑动联动效果。今天我们就模仿TabLayoutMediator来实现一个TabLayout与RecyclerView的锚点定位功能。效果如下图:

锚点定位
锚点定位

完整代码地址:TabLayoutMediator2

大致思路

思路是很简单的,

  1. 在每次tab选中的时候, 通过监听TabLayout的OnTabSelectedListener, 使RecyclerView滑动到对应位置
  2. 在RecyclerView滑动的时候,通过监听RecyclerView的OnScrollListener确定tab的选中位置
  3. Tab与RecyclerView中的Item的对应方式使用ViewType来实现,让每个tab绑定它所对应的RecyclerView中起始Item与末尾Item的ViewType。

代码思路

  1. TabConfigurationStrategy -- TabLayout创建tab的回调接口
 /**
  * A callback interface that must be implemented to set the text and styling of newly created
  * tabs.
  */
 interface TabConfigurationStrategy {
     /**
      * Called to configure the tab for the page at the specified position. Typically calls [ ][TabLayout.Tab.setText], but any form of styling can be applied.
      *
      * @param tab The Tab which should be configured to represent the title of the item at the given
      * position in the data set.
      * @param position The position of the item within the adapter's data set.
      * @return Adapter's first and last view type corresponding to the tab
      */
     fun onConfigureTab(tab: TabLayout.Tab, position: Int): IntArray
 }
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其中onConfigureTab的返回值即为该Tab对应RecylcerView中起始Item与末尾Item的ViewType的Array

  1. TabLayoutOnScrollListener -- 继承于RecyclerView.OnScrollListener(),并持有TabLayout,监听RecylcerView滑动时, 改变TabLayout中Tab的选中状态
   private class TabLayoutOnScrollListener(
       tabLayout: TabLayout
   ) : RecyclerView.OnScrollListener() {
       private var previousScrollState = 0
       private var scrollState = 0
       //是否是点击tab滚动
       var tabClickScroll: Boolean = false
       // TabLayout中Tab的选中状态
       var selectedTabPosition: Int = -1
   
       private val tabLayoutRef: WeakReference<TabLayout> = WeakReference(tabLayout)
   
       override fun onScrolled(recyclerView: RecyclerView, dx: Int, dy: Int) {
           super.onScrolled(recyclerView, dx, dy)
           if (tabClickScroll) {
               return
           }
           //当前可见的第一个Item
           val currItem = recyclerView.findFirstVisibleItemPosition()
           val viewType = recyclerView.adapter?.getItemViewType(currItem) ?: -1
           //根据Item的ViewType与TabLayout中Tab的ViewType的对应情况,选中对应tab
           val tabCount = tabLayoutRef.get()?.tabCount ?: 0
           for (i in 0 until tabCount) {
               val tab = tabLayoutRef.get()?.getTabAt(i)
               val viewTypeArray = tab?.tag as? IntArray
               if (viewTypeArray?.contains(viewType) == true) {
                   val updateText =
                       scrollState != RecyclerView.SCROLL_STATE_SETTLING || previousScrollState == RecyclerView.SCROLL_STATE_DRAGGING
                   val updateIndicator =
                       !(scrollState == RecyclerView.SCROLL_STATE_SETTLING && previousScrollState == RecyclerView.SCROLL_STATE_IDLE)
                   if (selectedTabPosition != i) {
                       selectedTabPosition = i
                       // setScrollPosition不会触发TabLayout的onTabSelected回调
                       tabLayoutRef.get()?.setScrollPosition(
                           i,
                           0f,
                           updateText,
                           updateIndicator
                       )
                       break
                   }
               }
           }
       }
   
       override fun onScrollStateChanged(recyclerView: RecyclerView, newState: Int) {
           super.onScrollStateChanged(recyclerView, newState)
           previousScrollState = scrollState
           scrollState = newState
           // 区分是手动滚动,还是调用代码滚动
           if (newState == RecyclerView.SCROLL_STATE_DRAGGING) {
               tabClickScroll = false
           }
       }
   }
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  1. RecyclerViewOnTabSelectedListener -- 继承TabLayout.OnTabSelectedListener, 监听TabLayout中Tab选中时,让RecyclerView滑动到对应位置,根据RecylerView要滑动到的位置此时需要区分3种情况

    1. 在屏幕中第一个可见Item之前,直接调用recyclerView.scrollToPosition滑动到对应位置
    2. 在屏幕第一个可见Item和最后一个可见Item之间,使用view.getTop()recyclerView.scrollBy(0, top)滑动到对应位置
    3. 在屏幕最后一个可见Item之后,先使用recyclerView.scrollToPosition让目标Item滑动到屏幕中可见,再使用recylerView.post{}, 走第二种情况,滑动到对应位置

    同时也兼容AppBarLayout,当需要滑动到最上方即position为0,展开AppBar, 其他情况折叠AppBar

   private class RecyclerViewOnTabSelectedListener(
       private val recyclerView: RecyclerView,
       private val moveRecyclerViewToPosition: (recyclerViewPosition: Int, tabPosition: Int) -> Unit
   ) : OnTabSelectedListener {
       override fun onTabSelected(tab: TabLayout.Tab) {
           moveRecyclerViewToPosition(tab)
       }
   
       override fun onTabUnselected(tab: TabLayout.Tab) {
       }
   
       override fun onTabReselected(tab: TabLayout.Tab) {
           moveRecyclerViewToPosition(tab)
       }
   
       private fun moveRecyclerViewToPosition(tab: TabLayout.Tab) {
           val viewType = (tab.tag as IntArray).first()
           val adapter = recyclerView.adapter
           val itemCount = adapter?.itemCount ?: 0
           for (i in 0 until itemCount) {
               if (adapter?.getItemViewType(i) == viewType) {
                   moveRecyclerViewToPosition.invoke(i, tab.position)
                   break
               }
           }
       }
   }
   
   private fun moveRecycleViewToPosition(recyclerViewPosition: Int, tabPosition: Int) {
       onScrollListener?.tabClickScroll = true
       onScrollListener?.selectedTabPosition = tabPosition
       val firstItem: Int = recyclerView.findFirstVisibleItemPosition()
       val lastItem: Int = recyclerView.findLastVisibleItemPosition()
       when {
           // Target position before firstItem
           recyclerViewPosition <= firstItem -> {
               recyclerView.scrollToPosition(recyclerViewPosition)
           }
           // Target position in firstItem .. lastItem
           recyclerViewPosition <= lastItem -> {
               val top: Int = recyclerView.getChildAt(recyclerViewPosition - firstItem).top
               recyclerView.scrollBy(0, top)
           }
           // Target position after lastItem
           else -> {
               recyclerView.scrollToPosition(recyclerViewPosition)
               recyclerView.post {
                   moveRecycleViewToPosition(recyclerViewPosition, tabPosition)
               }
           }
       }
       // If have appBar, expand or close it
       if (recyclerViewPosition == 0) {
           appBarLayout?.setExpanded(true, false)
       } else {
           appBarLayout?.setExpanded(false, false)
       }
   }
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  1. attach方法,初始化各种监听,绑定RecyclerView与TabLayout。

使用方法

使用起来非常简单,只需要新建一个TabLayoutMediator2并调用attach()就好了

val tabTextArrayList = arrayListOf("demo1", "demo2", "demo3")
val tabViewTypeArrayList = arrayListof(intArrayOf(1, 2), intArrayOf(7, 8), intArrayOf(9, 11))

TabLayoutMediator2(
    tabLayout = binding.layoutGoodsDetailTop.tabLayout,
    recyclerView = binding.recyclerView,
    tabCount = tabTextArrayList.size,
    appBarLayout = binding.appbar,
    autoRefresh = false,
    tabConfigurationStrategy = object : TabLayoutMediator2.TabConfigurationStrategy {
        override fun onConfigureTab(tab: TabLayout.Tab, position: Int): IntArray {
            tab.setText(tabTextArrayList[position])
            return tabViewTypeArrayList[position]
        }
    }
).apply {
    attach()
}
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最后

TabLayoutMediator2是模仿ViewPager2TabLayout的绑定类TabLayoutMediator实现的,使用简单,建议大家可以去看下原API的实现,如果有什么问题欢迎大家留言。

本文使用 mdnice 排版

分类:
Android
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分类:
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