前言

本文参考辉哥的博客RecyclerView更全解析之 - 打造通用的下拉刷新上拉加载进行实现，具体代码实现思路可查看原博客，目的是通过自定义RecyclerView自己实现添加头部、添加底部、上拉加载、下拉刷新功能。

最终效果

具体实现

• 自定义支持添加头部和底部的Adapter

/**
- 支持添加头部和底部的Adapter
- on 2022/11/7
*/
class WrapRecyclerAdapter(adapter: RecyclerView.Adapter<RecyclerView.ViewHolder>) :
   RecyclerView.Adapter<RecyclerView.ViewHolder>() {

   /**
    * 用来存放头部和底部的集合
    */
   private var headerView: SparseArray<View>
   private var footerView: SparseArray<View>

   //头部类型开始位置，用于viewType
   private var BASE_ITEM_TYPE_HEADER = 1000000

   //底部类型开始位置，用于viewType
   private var BASE_ITEM_TYPE_FOOTER = 2000000

   /**
    * 列表的adapter
    */
   private var adapter: RecyclerView.Adapter<RecyclerView.ViewHolder>

   init {
       this.adapter = adapter
       headerView = SparseArray()
       footerView = SparseArray()
   }


   override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): RecyclerView.ViewHolder {
       if (isHeaderViewType(viewType)) {
           val headerView = headerView.get(viewType)
           return createHeaderFooterViewHolder(headerView)
       }
       if (isFooterViewType(viewType)) {
           val footerView = footerView.get(viewType)
           return createHeaderFooterViewHolder(footerView)
       }
       return adapter.onCreateViewHolder(parent, viewType)
   }

   /**
    * 创建头部或底部的ViewHolder
    */
   private fun createHeaderFooterViewHolder(view: View): RecyclerView.ViewHolder {
       return object : RecyclerView.ViewHolder(view) {}
   }

   override fun onBindViewHolder(holder: RecyclerView.ViewHolder, position: Int) {
       //如果是头部或者底部item，不进行布局绑定
       if (isHeaderViewPosition(position) || isFooterViewPosition(position)) {
           return
       }
       val itemAdapterPosition = position - headerView.size()
       adapter.onBindViewHolder(holder, itemAdapterPosition)
   }

   override fun getItemViewType(position: Int): Int {
       if (isHeaderViewPosition(position)) {
           //如果是headerView
           return headerView.keyAt(position)
       }
       if (isFooterViewPosition(position)) {
           //如果是footerView
           val footerPosition = position - headerView.size() - adapter.itemCount
           return footerView.keyAt(footerPosition)
       }
       //则为普通adapter的ViewType
       val adapterPosition = position - headerView.size()
       return adapter.getItemViewType(adapterPosition)
   }


   override fun getItemCount(): Int {
       //条目为三者数量之和
       return adapter.itemCount + headerView.size() + footerView.size()
   }


   fun addHeaderView(view: View) {
       val position = headerView.indexOfValue(view)
       if (position < 0) {
           headerView.put(BASE_ITEM_TYPE_HEADER++, view)
       }
       notifyDataSetChanged()
   }

   fun removeHeaderView(view: View) {
       val position = headerView.indexOfValue(view)
       if (position < 0) {
           return
       }
       headerView.removeAt(position)
       notifyDataSetChanged()
   }

   fun getAdapter(): RecyclerView.Adapter<ViewHolder> {
       return adapter
   }

   fun addFooterView(view: View) {
       val position = footerView.indexOfValue(view)
       if (position < 0) {
           footerView.put(BASE_ITEM_TYPE_FOOTER++, view)
       }
       notifyDataSetChanged()
   }


   fun removeFooterView(view: View) {
       val position = footerView.indexOfValue(view)
       if (position < 0) {
           return
       }
       footerView.removeAt(position)
       notifyDataSetChanged()
   }

   private fun isHeaderViewType(viewType: Int): Boolean {
       val position = headerView.indexOfKey(viewType)
       return position >= 0
   }

   private fun isFooterViewType(viewType: Int): Boolean {
       val position = footerView.indexOfKey(viewType)
       return position >= 0
   }


   private fun isHeaderViewPosition(position: Int): Boolean {
       return position < headerView.size()
   }

   private fun isFooterViewPosition(position: Int): Boolean {
       return position >= headerView.size() + adapter.itemCount
   }


   /**
    * 解决GridLayoutManager添加头部和底部不占用一行的问题
    */
   fun adjustSpanSize(recyclerView: RecyclerView) {
       if (recyclerView.layoutManager is GridLayoutManager) {
           val layoutManager = recyclerView.layoutManager as GridLayoutManager
           layoutManager.spanSizeLookup = object : GridLayoutManager.SpanSizeLookup() {
               override fun getSpanSize(position: Int): Int {
                   val isHeaderOrFooter =
                       isHeaderViewPosition(position) || isFooterViewPosition(position)
                   return if (isHeaderOrFooter) {
                       layoutManager.spanCount
                   } else {
                       1
                   }
               }

           }
       }
   }

• 自定义可以添加头部和底部的RecyclerView

/**
- 可以添加头部和底部的RecyclerView
- on 2022/11/7
*/
open class WrapRecyclerView : RecyclerView {
   constructor(context: Context) : super(context)
   constructor(context: Context, attrs: AttributeSet?) : super(context, attrs)
   constructor(context: Context, attrs: AttributeSet?, defStyleAttr: Int) : super(
       context,
       attrs,
       defStyleAttr
   )


   /**
    * 包裹了头部和底部的adapter
    */
   private var wrapRecyclerAdapter: WrapRecyclerAdapter? = null

   /**
    * 列表对应的list
    */
   private var mAdapter: Adapter<ViewHolder>? = null

   /**
    * 增加一些通用功能
    * 空列表数据应该显示emptyView
    * 正在加载数据页面
    */
   private var emptyView: View? = null
   private var loadView: View? = null


   private var mDataObserver = object : AdapterDataObserver() {
       override fun onChanged() {
           if (mAdapter == null) {
               return
           }
           //观察者，列表adapter更新，包裹的也需要更新
           if (wrapRecyclerAdapter != adapter) {
               wrapRecyclerAdapter?.notifyDataSetChanged()
           }
           dataChanged()

       }

       override fun onItemRangeRemoved(positionStart: Int, itemCount: Int) {
           if (mAdapter == null) {
               return
           }
           if (wrapRecyclerAdapter != adapter) {
               wrapRecyclerAdapter?.notifyItemRangeRemoved(positionStart, itemCount)
           }
           dataChanged()
       }

       override fun onItemRangeChanged(positionStart: Int, itemCount: Int) {
           if (mAdapter == null) {
               return
           }
           if (wrapRecyclerAdapter != adapter) {
               wrapRecyclerAdapter?.notifyItemChanged(positionStart, itemCount)
           }
           dataChanged()
       }

       override fun onItemRangeChanged(positionStart: Int, itemCount: Int, payload: Any?) {
           if (mAdapter == null) {
               return
           }
           if (wrapRecyclerAdapter != adapter) {
               wrapRecyclerAdapter?.notifyItemRangeChanged(positionStart, itemCount, payload)
           }
           dataChanged()
       }

       override fun onItemRangeInserted(positionStart: Int, itemCount: Int) {
           if (mAdapter == null) {
               return
           }
           if (wrapRecyclerAdapter != adapter) {
               wrapRecyclerAdapter?.notifyItemRangeInserted(positionStart, itemCount)
           }
           dataChanged()
       }

       override fun onItemRangeMoved(fromPosition: Int, toPosition: Int, itemCount: Int) {
           if (mAdapter == null) {
               return
           }
           if (wrapRecyclerAdapter != adapter) {
               wrapRecyclerAdapter?.notifyItemRangeRemoved(fromPosition, toPosition)
           }
           dataChanged()
       }
   }


   private fun dataChanged() {
       if (adapter?.itemCount == 0) {
           emptyView?.visibility = VISIBLE
       }
   }

   fun addEmptyView(view: View) {
       this.emptyView = view
   }

   fun addLoadingView(loadingView: View) {
       this.loadView = loadingView
       loadingView.visibility = VISIBLE
   }


   override fun setAdapter(adapter: Adapter<*>?) {
       //防止多次设置Adapter
       if (mAdapter != null) {
           mAdapter!!.unregisterAdapterDataObserver(mDataObserver)
           mAdapter = null
       }
       this.mAdapter = adapter as Adapter<ViewHolder>?

       wrapRecyclerAdapter = if (adapter is WrapRecyclerAdapter) {
           adapter
       } else {
           WrapRecyclerAdapter(adapter as Adapter<ViewHolder>)
       }
       super.setAdapter(wrapRecyclerAdapter)
       //注册一个观察者
       mAdapter!!.registerAdapterDataObserver(mDataObserver)
       //解决GridLayoutManager添加头部和底部不占据一行问题
       wrapRecyclerAdapter!!.adjustSpanSize(this)

       //加载数据页面
       if (loadView != null && loadView!!.visibility == View.VISIBLE) {
           loadView?.visibility = GONE
       }
   }

   /**
    * 添加头部
    */
   fun addHeaderView(view: View) {
       wrapRecyclerAdapter?.addHeaderView(view)
   }

   /**
    * 添加底部
    */
   fun addFooterView(view: View) {
       wrapRecyclerAdapter?.addFooterView(view)
   }

   fun removeHeaderView(view: View) {
       wrapRecyclerAdapter?.removeHeaderView(view)
   }

   fun removeFooterView(view: View) {
       wrapRecyclerAdapter?.removeFooterView(view)
   }

• 为了更好的扩展下拉刷新，新增下拉刷新辅助抽象类

/**
- 下拉刷新的辅助类
- on 2022/11/7
*/
abstract class RefreshViewCreator {

   /**
    * 获取下拉刷新的View
    * @param context 上下文参数
    * @param parent 父容器  RecyclerView
    */
   abstract fun getRefreshView(context: Context, parent: ViewGroup): View

   /**
    * 正在下拉
    * @param currentDragHeight 当前拖动的高度
    * @param refreshViewHeight 整体刷新View的高度
    * @param currentRefreshStatus 当前状态
    *
    */
   abstract fun onPull(currentDragHeight: Int, refreshViewHeight: Int, currentRefreshStatus: Int)

   /**
    * 正在刷新中
    */
   abstract fun onRefreshing()

   /**
    * 停止刷新
    */
   abstract fun onStopRefresh()
}

• 自定义支持下拉刷新的RefreshRecyclerView

/**
- 下拉刷新的RecyclerView
- on 2022/11/7
*/
open class RefreshRecyclerView : WrapRecyclerView {
   constructor(context: Context) : super(context)
   constructor(context: Context, attrs: AttributeSet?) : super(context, attrs)
   constructor(context: Context, attrs: AttributeSet?, defStyleAttr: Int) : super(
       context, attrs, defStyleAttr
   )

   //下拉刷新的辅助类
   private var refreshCreator: RefreshViewCreator? = null

   //下拉刷新头部的高度
   private var refreshViewHeight = 0

   //下拉刷新的头部View
   private var refreshView: View? = null

   //手指按下Y的位置
   private var fingerDownY = 0

   //手指拖拽的阻力指数
   open var dragIndex = 0.35f

   //当前是否正在拖动
   private var currentDrag = false

   //当前状态
   private var currentRefreshStatus = 0

   // 默认状态
   private val REFRESH_STATUS_NORMAL = 1

   //下拉刷新状态
   private val REFRESH_STATUS_PULL_DOWN_REFRESHING = 2

   //松开刷新状态
   private val REFRESH_STATUS_LOOSEN_REFRESHING = 3

   //正在刷新状态
   private val REFRESH_STATUS_REFRESHING = 4


   fun addRefreshViewCreator(refreshViewCreator: RefreshViewCreator) {
       this.refreshCreator = refreshViewCreator
       addRefreshView()
   }

   override fun setAdapter(adapter: Adapter<*>?) {
       super.setAdapter(adapter)
       addRefreshView()
   }


   override fun dispatchTouchEvent(ev: MotionEvent): Boolean {
       when (ev.action) {
           MotionEvent.ACTION_DOWN -> {
               //记录手指按下的位置
               fingerDownY = ev.rawY.toInt()
           }
           MotionEvent.ACTION_UP -> {
               if (currentDrag) {
                   restoreRefreshView()
               }
           }
       }
       return super.dispatchTouchEvent(ev)
   }

   /**
    * 重置当前刷新状态
    */
   private fun restoreRefreshView() {
       val currentTopMargin = (refreshView?.layoutParams as MarginLayoutParams).topMargin
       var finalTopMargin = -refreshViewHeight + 1
       if (currentRefreshStatus == REFRESH_STATUS_LOOSEN_REFRESHING) {
           finalTopMargin = 0
           currentRefreshStatus = REFRESH_STATUS_REFRESHING
           refreshCreator?.onRefreshing()
           listener?.onRefresh()
       }

       val distance = currentTopMargin - finalTopMargin

       //回弹到指定位置

       val animator: ValueAnimator =
           ObjectAnimator.ofFloat(currentTopMargin.toFloat(), finalTopMargin.toFloat())
               .setDuration(distance.toLong())
       animator.addUpdateListener {
           val currentTopMargin = it.animatedValue as Float
           setRefreshViewMarginTop(currentTopMargin.toInt())
       }

       animator.start()
       currentDrag = false

   }


   override fun onTouchEvent(ev: MotionEvent): Boolean {
       when (ev.action) {
           MotionEvent.ACTION_MOVE -> {
               //在最顶部的时候才处理，否则不需要处理
               if (canScrollUp() || currentRefreshStatus == REFRESH_STATUS_REFRESHING || refreshView == null || refreshCreator == null) {
                   //如果没有到达最顶端，也就是说还可以向上滚动就什么都不处理
                   return super.onTouchEvent(ev)
               }
               //解决下拉刷新自动滚动问题
               if (currentDrag) {
                   scrollToPosition(0)
               }
               //获取手指触摸拖拽的距离
               val distanceY = (ev.rawY - fingerDownY) * dragIndex
               //如果是已经到达头部，并且不断的向上拉，那么不断的改变refreshView的marginTop的值
               if (distanceY > 0) {
                   val marginTop = distanceY - refreshViewHeight
                   setRefreshViewMarginTop(marginTop.toInt())
                   updateRefreshStatus(distanceY)
                   currentDrag = true
                   return false
               }
           }
       }
       return super.onTouchEvent(ev)
   }


   /**
    * 更新刷新状态
    */
   private fun updateRefreshStatus(distanceY: Float) {
       currentRefreshStatus = if (distanceY <= 0) {
           REFRESH_STATUS_NORMAL
       } else if (distanceY < refreshViewHeight) {
           REFRESH_STATUS_PULL_DOWN_REFRESHING
       } else {
           REFRESH_STATUS_LOOSEN_REFRESHING
       }
       refreshCreator?.onPull(distanceY.toInt(), refreshViewHeight, currentRefreshStatus)

   }


   /**
    * 添加头部刷新View
    */
   private fun addRefreshView() {
       if (adapter != null && refreshCreator != null) {
           val refreshView = refreshCreator?.getRefreshView(context, this)
           if (refreshView != null) {
               addHeaderView(refreshView)
               this.refreshView = refreshView
           }
       }
   }

   override fun onLayout(changed: Boolean, l: Int, t: Int, r: Int, b: Int) {
       super.onLayout(changed, l, t, r, b)
       if (refreshView != null && refreshViewHeight <= 0) {
           //获取头部刷新View的高度
           refreshViewHeight = refreshView?.measuredHeight!!
           if (refreshViewHeight > 0) {
               //隐藏头部刷新的View  marginTop 多留出1px防止无法判断是不是滑动到头部问题
               setRefreshViewMarginTop(-refreshViewHeight + 1)
           }
       }
   }

   private fun setRefreshViewMarginTop(marginTop: Int) {
       var finalMarginTop = marginTop
       val params = refreshView?.layoutParams as MarginLayoutParams
       if (finalMarginTop < -refreshViewHeight + 1) {
           finalMarginTop = -refreshViewHeight + 1
       }
       params.topMargin = finalMarginTop
       refreshView?.layoutParams = params
   }


   private fun canScrollUp(): Boolean {
       return canScrollVertically(-1) || scrollY > 0
   }


   fun onStopRefresh() {
       currentRefreshStatus = REFRESH_STATUS_NORMAL
       restoreRefreshView()
       refreshCreator?.onStopRefresh()
   }


   private var listener: OnRefreshListener? = null

   fun setOnRefreshListener(listener: OnRefreshListener) {
       this.listener = listener
   }

   interface OnRefreshListener {
       fun onRefresh()
   }

• 具体的下拉刷新类以及布局文件

/**
* on 2022/11/7
*/
class CommonRefreshCreator : RefreshViewCreator() {
   private var refreshView: View? = null

   override fun getRefreshView(context: Context, parent: ViewGroup): View {
       val view =
           LayoutInflater.from(context).inflate(R.layout.layout_progressbar, parent,false)
       refreshView = view.findViewById(R.id.pb)
       return view
   }

   override fun onPull(currentDragHeight: Int, refreshViewHeight: Int, currentRefreshStatus: Int) {
       val rotate = currentDragHeight / refreshViewHeight
       //不断下拉的过程中不断旋转图片
       refreshView!!.rotation = (rotate * 360).toFloat()
   }

   override fun onRefreshing() {
       //刷新的时候也不断旋转
       val animation = RotateAnimation(
           0f,
           720f,
           Animation.RELATIVE_TO_SELF,
           0.5F,
           Animation.RELATIVE_TO_SELF,
           0.5f
       )
       animation.repeatCount = -1
       animation.duration = 2000
       refreshView!!.startAnimation(animation)
   }

   override fun onStopRefresh() {
       //停止的时候清除动画
       refreshView!!.rotation = 0f
       refreshView!!.clearAnimation()
   }
}

### layout_progressbar
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
   android:layout_width="match_parent"
   android:layout_height="80dp">

   <ProgressBar
       android:indeterminateDuration="1000"
       android:max="360"
       android:id="@+id/pb"
       android:layout_width="50dp"
       android:layout_height="50dp"
       android:layout_centerInParent="true" />
</RelativeLayout>

• 支持上拉加载下拉刷新的RecyclerView

/**
- 支持上拉加载 下拉刷新的RecyclerView
- on 2022/11/7
*/
class LoadRefreshRecyclerView : RefreshRecyclerView {

   constructor(context: Context) : super(context)
   constructor(context: Context, attrs: AttributeSet?) : super(context, attrs)
   constructor(context: Context, attrs: AttributeSet?, defStyleAttr: Int) : super(
       context,
       attrs,
       defStyleAttr
   )

   //上拉加载更多的辅助类
   private var loadViewCreator: LoadViewCreator? = null

   //上拉加载更多头部的高度
   private var loadViewHeight = 0

   //上拉加载更多的头部View
   private var loadView: View? = null

   //手指按下的位置
   private var fingerDownY = 0

   //当前是否正在拖动
   private var currentDrag = false

   //当前状态
   private var currentLoadStatus = 0

   companion object{
       //默认状态
        var LOAD_STATUS_NORMAL = 10

       //上拉加载更多状态
        var LOAD_STATUS_PULL_DOWN_REFRESH = 11

       //松开加载更多状态
        var LOAD_STATUS_LOOSEN_LOADING = 12

       //正在加载更多状态
         var LOAD_STATUS_LOADING = 13
   }

   //设置上拉加载更多
   fun addLoadViewCreator(loadViewCreator: LoadViewCreator) {
       this.loadViewCreator = loadViewCreator
       addLoadView()
   }

   override fun setAdapter(adapter: Adapter<*>?) {
       super.setAdapter(adapter)
       addLoadView()
   }

   override fun dispatchTouchEvent(ev: MotionEvent): Boolean {
       when (ev.action) {
           MotionEvent.ACTION_DOWN -> {
               //记录手指按下的位置,之所以写在dispatchTouchEvent里是因为如果我们处理了item点击事件，那么就不会进入onTouchEvent里面，所有应该在这里处理
               fingerDownY = ev.rawY.toInt()
           }
           MotionEvent.ACTION_UP -> {
               if (currentDrag) {
                   restoreLoadView()
               }
           }
       }
       return super.dispatchTouchEvent(ev)
   }

   /**
    * 重置上拉加载更多View
    */
   private fun restoreLoadView() {
       var currentBottomMargin = (loadView?.layoutParams as MarginLayoutParams).bottomMargin
       var finalBottomMargin = 0
       if (currentLoadStatus == LOAD_STATUS_LOOSEN_LOADING) {
           currentLoadStatus = LOAD_STATUS_LOADING
           loadViewCreator?.onLoading()
           listener?.onLoad()
       }

       val distance = currentBottomMargin - finalBottomMargin
       //回弹到指定位置
       val animator =
           ObjectAnimator.ofFloat(currentBottomMargin.toFloat(), finalBottomMargin.toFloat())
               .setDuration(distance.toLong())
       animator.addUpdateListener {
           val currentTopMargin = it.animatedValue
           setLoadViewMarginBottom(currentTopMargin as Float)
       }
       animator.start()
       currentDrag = false
   }

   override fun onLayout(changed: Boolean, l: Int, t: Int, r: Int, b: Int) {
       super.onLayout(changed, l, t, r, b)
       if (loadViewCreator != null && loadView != null) {
           loadViewHeight = loadView!!.measuredHeight
       }
   }

   override fun onTouchEvent(ev: MotionEvent): Boolean {
       when (ev.action) {
           MotionEvent.ACTION_MOVE -> {
               //当在最底部的时候才处理，否则不需要处理
               if (canScrollDown() || currentLoadStatus == LOAD_STATUS_LOADING) {
                   return super.onTouchEvent(ev)
               }
               //解决上拉加载更多自动滚动问题
               if (currentDrag) {
                   scrollToPosition(adapter!!.itemCount - 1)
               }

               //获取手指触摸拖拽的距离
               val distanceY = (ev.rawY - fingerDownY) * dragIndex
               //如果是已经到达底部，并且不断的向下拉，那么不断的改变marginBottom的值
               if (distanceY < 0) {
                   setLoadViewMarginBottom(-distanceY)
                   updateLoadStatus(-distanceY)
                   currentDrag = true
                   return true
               }
           }
       }
       return super.onTouchEvent(ev)
   }


   /**
    * 设置加载View的marginBottom
    */
   private fun setLoadViewMarginBottom(marginBottom: Float) {
       var finalMarginBottom = marginBottom.toInt()
       val marginLayoutParams = loadView!!.layoutParams as MarginLayoutParams
       if (finalMarginBottom < 0) {
           finalMarginBottom = 0
       }
       marginLayoutParams.bottomMargin = finalMarginBottom
       loadView?.layoutParams = marginLayoutParams
   }


   private fun canScrollDown(): Boolean {
       return canScrollVertically(1)
   }


   /**
    * 停止加载更多
    */
   fun onStopLoad() {
       currentLoadStatus = LOAD_STATUS_NORMAL
       restoreLoadView()
       loadViewCreator?.onStopLoad()
   }

   private fun updateLoadStatus(distanceY: Float) {
       currentLoadStatus = if (distanceY <= 0) {
           LOAD_STATUS_NORMAL
       } else if (distanceY < loadViewHeight) {
           LOAD_STATUS_PULL_DOWN_REFRESH
       } else {
           LOAD_STATUS_LOOSEN_LOADING
       }
       loadViewCreator?.onPull(distanceY.toInt(), loadViewHeight, currentLoadStatus)
   }

   private fun addLoadView() {
       if (adapter != null && loadViewCreator != null) {
           //添加底部加载更多View
           val view = loadViewCreator?.getLoadView(context, this)
           if (view != null) {
               addFooterView(view)
               this.loadView = view
           }
       }
   }

   private var listener: OnLoadMoreListener? = null
   fun setOnLoadMoreListener(listener: OnLoadMoreListener) {
       this.listener = listener
   }

   interface OnLoadMoreListener {
       fun onLoad()
   }
}

• 上拉加载更多辅助抽象类

/**
- 上拉加载更多辅助类
- on 2022/11/8
*/
abstract class LoadViewCreator {
   /**
    * 获取上拉加载更多的View
    */
   abstract fun getLoadView(context: Context, parent: ViewGroup): View

   /**
    * 正在上拉
    * @param currentDragHeight 当前拖动的距离
    * @param loadViewHeight 总的加载高度
    * @param currentLoadStatus 当前状态
    */
   abstract fun onPull(currentDragHeight: Int, loadViewHeight: Int, currentLoadStatus: Int)

   /**
    * 正在加载中
    */
   abstract fun onLoading()

   /**
    * 停止加载
    */
   abstract fun onStopLoad()
}

• 上拉加载更多具体实现类以及对应布局文件

class CommonLoadCreator : LoadViewCreator() {
   private var tv: TextView? = null
   private var pb: ProgressBar? = null
   private var loadView: View? = null
   override fun getLoadView(context: Context, parent: ViewGroup): View {
       val loadView: View =
           LayoutInflater.from(context).inflate(R.layout.layout_load_footer_view, parent, false)
       tv = loadView.findViewById(R.id.tv)
       pb = loadView.findViewById(R.id.pb)
       this.loadView = loadView
       return loadView
   }

   override fun onPull(currentDragHeight: Int, loadViewHeight: Int, currentLoadStatus: Int) {
       if (currentLoadStatus == LoadRefreshRecyclerView.LOAD_STATUS_PULL_DOWN_REFRESH) {
           tv?.text = "上拉加载更多"
       }
       if (currentLoadStatus == LoadRefreshRecyclerView.LOAD_STATUS_LOOSEN_LOADING) {
           tv?.text = "松开加载更多"
       }
   }

   override fun onLoading() {
       tv?.visibility = View.GONE
       pb?.visibility = View.VISIBLE
       val animation = RotateAnimation(
           0f,
           720f,
           Animation.RELATIVE_TO_SELF,
           0.5f,
           Animation.RELATIVE_TO_SELF,
           0.5f
       )
       animation.duration = 2000
       animation.repeatCount = -1
       pb?.startAnimation(animation)
   }

   override fun onStopLoad() {
       //停止加载的时候
       pb?.rotation = 0f
       pb?.clearAnimation()
       pb?.visibility = View.GONE
       tv?.text = "上拉加载更多"
       tv?.visibility = View.VISIBLE
   }
}

### layout_load_footer_view
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
   android:layout_width="match_parent"
   android:layout_height="60dp"
   android:gravity="center">

   <ProgressBar
       android:id="@+id/pb"
       android:layout_width="50dp"
       android:layout_height="50dp"
       android:layout_centerVertical="true"
       android:indeterminateDuration="1000"
       android:max="360" />

   <TextView
       android:id="@+id/tv"
       android:layout_width="wrap_content"
       android:layout_height="wrap_content"
       android:layout_centerVertical="true"
       android:layout_marginLeft="10dp"
       android:layout_toRightOf="@+id/pb"
       android:text="上拉加载更多" />

</RelativeLayout>

测试代码

class RecyclerActivity : AppCompatActivity() {
    private val list = mutableListOf<String>()
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_recycler)
        for (i in 0..50) {
            list.add("$i")
        }
        val rlv = findViewById<LoadRefreshRecyclerView>(R.id.rlv)
        rlv.layoutManager = GridLayoutManager(this, 4)
        val adapter = CommonItemAdapter(this, list)
        rlv.adapter = adapter
        val headerView =
            LayoutInflater.from(this).inflate(R.layout.layout_recycler_header, rlv, false)
        val footerView =
            LayoutInflater.from(this).inflate(R.layout.layout_recycler_footer, rlv, false)
        //设置上拉刷新
        rlv.addRefreshViewCreator(CommonRefreshCreator())
        //添加Header
        rlv.addHeaderView(headerView)
        //添加Footer
        rlv.addFooterView(footerView)
        //添加下拉加载更多 【由于内部是通过addView实现，存在添加顺序，需要注意】
        rlv.addLoadViewCreator(CommonLoadCreator())
        rlv.setOnRefreshListener(object : RefreshRecyclerView.OnRefreshListener {
            override fun onRefresh() {
                rlv.postDelayed({
                    rlv.onStopRefresh()
                }, 2000)
            }

        })
        rlv.setOnLoadMoreListener(object : LoadRefreshRecyclerView.OnLoadMoreListener {
            override fun onLoad() {
                rlv.postDelayed({
                    rlv.onStopLoad()
                }, 2000)
            }

        })

    }

}

总结

通过自己动手实现一套下拉刷新上拉加载框架，了解了RecyclerView添加Header以及Footer的实现原理，通过本次学习也看到了代码剥离拆分以及设计模式运用的重要性，写代码一定要多思考，才能写出让人赏心悦目的代码。