Android RecycleView实现滑动停止后自动吸附效果

package com.example.testapp
 
import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import androidx.recyclerview.widget.LinearLayoutManager
import androidx.recyclerview.widget.RecyclerView
import com.example.testapp.code.note.JoinData
import com.example.testapp.code.note.TheatreJoinerAdapter
import kotlinx.android.synthetic.main.activity_main.*
 
class MainActivity : AppCompatActivity() {
 
  //isUserControl 表示是否是 第二次定位滑动
  @Volatile
  private var isUserControl = false
  var runnable = Runnable {
    smoothScrollToPosition()//处理rcy定位
  }
 
  val list = arrayListOf<JoinData>()
  override fun onCreate(savedInstanceState: Bundle&#63;) {
    super.onCreate(savedInstanceState)
    setContentView(R.layout.activity_main)
    for (i in 0..50) {
      list.add(JoinData("小名${i}", i))
    }
    rcy.layoutManager = LinearLayoutManager(this, LinearLayoutManager.VERTICAL, false)
    var adapter = TheatreJoinerAdapter(this, list)
    rcy.adapter = adapter
    rcy.addOnScrollListener(object : RecyclerView.OnScrollListener() {
      override fun onScrolled(r: RecyclerView, dx: Int, dy: Int) {
        super.onScrolled(r, dx, dy)
        //判断是否是自动滚动
        if (r.scrollState == RecyclerView.SCROLL_STATE_SETTLING && !isUserControl) {//自动滚动
          //滚动幅度 在 -3 .. 3以内 其实时接近停止了 慢速滑动了 这时我们让他停止
          if (dy in -3..3) {//向下滚动
            r.stopScroll()
          }
        }
      }
 
      override fun onScrollStateChanged(r: RecyclerView, newState: Int) {
        super.onScrollStateChanged(r, newState)
        if (newState == RecyclerView.SCROLL_STATE_IDLE) {//滑动停止
          if (!isUserControl) {
            rcy.postDelayed(runnable, 200)//200 毫秒延时任务
          }
        }
        if (r.scrollState != RecyclerView.SCROLL_STATE_SETTLING) {//非自动滑动
          isUserControl = false
        }
      }
    })
  }
 
  private fun smoothScrollToPosition() {
    isUserControl = true
    val stickyInfoView = rcy.getChildAt(0) //获取头部View 第一个view
    val bottom = stickyInfoView.bottom//获取view底部到rcy的顶部高度
    val height = stickyInfoView.measuredHeight//获取view高度
    if (bottom != height) {//去除正好停在正好的位置的情况
      if (bottom >= (height / 2)) {//判断view在上一半还是在下一半
        rcy.smoothScrollBy(0, -(height - bottom))//二次滑动
      } else {
        rcy.smoothScrollBy(0, bottom)//二次滑动
      }
    }
  }
}