微信小程序实现拖拽 image 触摸事件监听

<image class="image-style" src="../../images/gundong.png" bindtap="ballClickEvent" style="bottom:{{ballBottom}}px;right:{{ballRight}}px;" bindtouchmove="ballMoveEvent">  
</image>

//index.js 
//获取应用实例 
var app = getApp() 
Page({ 
 data: { 
  ballBottom: 240, 
  ballRight: 120, 
  screenHeight: 0, 
  screenWidth: 0, 
 }, 
 onLoad: function () { //获取屏幕宽高 
  var _this = this; 
  wx.getSystemInfo({ 
   success: function (res) { 
    _this.setData({ 
     screenHeight: res.windowHeight, 
     screenWidth: res.windowWidth, 
    }); 
   } 
  }); 
 }, 
 ballMoveEvent: function (e) { 
  console.log('我被拖动了....') 
  var touchs = e.touches[0]; 
  var pageX = touchs.pageX; 
  var pageY = touchs.pageY; 
  console.log('pageX: ' + pageX) 
  console.log('pageY: ' + pageY) 

//防止坐标越界,view宽高的一般 
  if (pageX < 30) return; 
  if (pageX > this.data.screenWidth - 30) return; 
  if (this.data.screenHeight - pageY <= 30) return; 
  if (pageY <= 30) return; 

//这里用right和bottom.所以需要将pageX pageY转换 
  var x = this.data.screenWidth - pageX - 30; 
  var y = this.data.screenHeight - pageY - 30; 
  console.log('x: ' + x) 
  console.log('y: ' + y) 
  this.setData({ 
   ballBottom: y, 
   ballRight: x 
  }); 
 }, 

//点击事件 
 ballClickEvent: function () { 
  console.log('点击了....') 
 } 
})

.image-style{ 
 position: absolute; 
 bottom: 240px; 
 right: 100px; 
 width: 60px; 
 height: 60px; 
 z-index: 100; 
}