Android RecycleView滑动停止后自动吸附效果的实现代码(滑动定位)

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?) {
  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
   }
  }
 }
}