微信小程序实现listview带字母滑动

handlerAlphaTap(e) {
  var ap = e.target.dataset.loc; //字母
  this.setData({
   locationTo: ap
  });

  var list = this.data.groups;
  this.offsetTop = (this.data.clientHeihgt - list.length * 16) / 2;

 },

 handlerMove(e) {
  var _this = this;
  var list = this.data.groups;
  var moveY = e.touches[0].clientY;
  var rY = moveY - this.offsetTop;
  if (rY >= 0) {
   var index = Math.ceil((rY - 16) / 16);
   if (0 <= index && index