RecyclerViewHelper

提供了注册加载更多，和判断是否不足一屏等工具方法

import androidx.recyclerview.widget.GridLayoutManager
import androidx.recyclerview.widget.LinearLayoutManager
import androidx.recyclerview.widget.RecyclerView
import androidx.recyclerview.widget.StaggeredGridLayoutManager

object RecyclerViewHelper {
  /**
   * RecyclerView 注册加载更多监听
   */
  @JvmStatic
  fun addOnScrollListener(recyclerView: RecyclerView, loadMore: () -> Unit) {
    recyclerView.addOnScrollListener(object : RecyclerView.OnScrollListener() {
      override fun onScrollStateChanged(recyclerView: RecyclerView, newState: Int) {
        super.onScrollStateChanged(recyclerView, newState)
        if (newState == RecyclerView.SCROLL_STATE_IDLE) {
          val layoutManager = recyclerView.layoutManager
          if (layoutManager is LinearLayoutManager) {
            val lastPosition = layoutManager.findLastCompletelyVisibleItemPosition()
            val count = layoutManager.itemCount
            if (lastPosition >= count - 2) {
              loadMore()
              return@onScrollStateChanged
            }
          } else if (layoutManager is StaggeredGridLayoutManager) {
            val spanCount = layoutManager.spanCount
            val count = layoutManager.itemCount
            val result = IntArray(spanCount)
            layoutManager.findLastCompletelyVisibleItemPositions(result)
            for (it in result) {
              if (it >= count - spanCount - 1) {
                loadMore()
                return@onScrollStateChanged
              }
            }
          } else if (layoutManager is GridLayoutManager) {
            val spanCount = layoutManager.spanCount
            val count = layoutManager.itemCount
            val lastPosition = layoutManager.findLastCompletelyVisibleItemPosition()
            if (lastPosition >= count - spanCount - 1) {
              loadMore()
              return@onScrollStateChanged
            }

          }
        }
      }
    })
  }


  /**
     * 判断是否一屏显示
     *
     * 错误或者空了返回 false
     */
  @JvmStatic
  fun isOneScreen(recyclerView: RecyclerView?): Boolean {
    recyclerView?.let {
      val layoutManager = recyclerView.layoutManager
      if (layoutManager is LinearLayoutManager) {
        // include GridLayoutManager
        val count = layoutManager.itemCount
        return count > 0 &&
        layoutManager.findFirstCompletelyVisibleItemPosition() == 0 &&
        layoutManager.findLastCompletelyVisibleItemPosition() == count - 1
      } else if (layoutManager is StaggeredGridLayoutManager) {
        val spanCount = layoutManager.spanCount
        val count = layoutManager.itemCount
        val last = IntArray(spanCount)
        val first = IntArray(spanCount)
        layoutManager.findLastCompletelyVisibleItemPositions(last)
        layoutManager.findFirstCompletelyVisibleItemPositions(first)
        return count > 0 && first.min() == 0 && last.max() == count - 1
      }
    }

    return false
  }

  private fun IntArray.min(): Int {
    if (this.isNotEmpty()) {
      var result = this[0]
      this.forEach {
        if (result > it) result = it
      }
      return result
    }
    return -1
  }

  private fun IntArray.max(): Int {
    if (this.isNotEmpty()) {
      var result = this[0]
      this.forEach {
        if (result < it) result = it
      }
      return result
    }
    return -1
  }
}