Android RecycleView實(shí)現(xiàn)滑動(dòng)停止后自動(dòng)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 第二次定位滑動(dòng)
  @Volatile
  private var isUserControl = false
  var runnable = Runnable {
    smoothScrollToPosition()//處理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)
        //判斷是否是自動(dòng)滾動(dòng)
        if (r.scrollState == RecyclerView.SCROLL_STATE_SETTLING && !isUserControl) {//自動(dòng)滾動(dòng)
          //滾動(dòng)幅度 在 -3 .. 3以內(nèi) 其實(shí)時(shí)接近停止了 慢速滑動(dòng)了 這時(shí)我們讓他停止
          if (dy in -3..3) {//向下滾動(dòng)
            r.stopScroll()
          }
        }
      }
 
      override fun onScrollStateChanged(r: RecyclerView, newState: Int) {
        super.onScrollStateChanged(r, newState)
        if (newState == RecyclerView.SCROLL_STATE_IDLE) {//滑動(dòng)停止
          if (!isUserControl) {
            rcy.postDelayed(runnable, 200)//200 毫秒延時(shí)任務(wù)
          }
        }
        if (r.scrollState != RecyclerView.SCROLL_STATE_SETTLING) {//非自動(dòng)滑動(dòng)
          isUserControl = false
        }
      }
    })
  }
 
  private fun smoothScrollToPosition() {
    isUserControl = true
    val stickyInfoView = rcy.getChildAt(0) //獲取頭部View 第一個(gè)view
    val bottom = stickyInfoView.bottom//獲取view底部到rcy的頂部高度
    val height = stickyInfoView.measuredHeight//獲取view高度
    if (bottom != height) {//去除正好停在正好的位置的情況
      if (bottom >= (height / 2)) {//判斷view在上一半還是在下一半
        rcy.smoothScrollBy(0, -(height - bottom))//二次滑動(dòng)
      } else {
        rcy.smoothScrollBy(0, bottom)//二次滑動(dòng)
      }
    }
  }
}