Implementation of image drag and drop function in WeChat applet development

<view class="container" style="height:{{screenHeight}}px;" >
	<view class="cnt">
		<image class="image-style" src="../uploads/2.jpg" style="width:
		{{imgwidth}}px;height:{{imgheight}}px;"bindtouchstart="startEvent"
		 bindtouchmove="moveEvent"bindload="imageLoad"animation="
		 {{animationData}}"bindtouchend="endEvent">
		</image>
	</view>
</view>

.container {
    box-sizing:border-box;
    padding:1rem;
} 
.cnt{
    width:100%;
    height:70%;
    border: 1px solid #ccc;
    position:relative;
    overflow: hidden;
    z-index:9999;
}
.image-style{
	-webkit-transform:translate(-38px,0px);  
}

var app = getApp()
Page({
	data: {
    	imgwidth:0,
    	imgheight:0,
    	animationData: {},
    	movex:0,
    	movey:0,
    	x:0,
    	y:0,
	},
	onLoad: function() {
		 // 页面初始化 options为页面跳转所带来的参数
		var _this = this;
		wx.getSystemInfo({
			success: function(res) {
				_this.setData({
					screenHeight: res.windowHeight,
					screenWidth: res.windowWidth,
				});
			}
		});
	},
	onReady:function(){
	    // 页面渲染完成
	    //实例化一个动画
	    this.animation = wx.createAnimation({
	    	duration: 1000, 
	    	timingFunction: 'linear',//均匀
	    	transformOrigin: "left top 0px",
	    })
	},
	imageLoad: function(e) {  
        var _this=this; 
        //1.框的宽高
        var cnt_offetw=_this.data.screenWidth-38,
        	cnt_offeth=(_this.data.screenHeight-38)*0.7;
        //2.获取图片真实宽度
        var $width=e.detail.width,    //获取图片真实宽度  
            $height=e.detail.height,  
            ratio=$width/$height;   //图片的真实宽高比例
       	//3.进行判断:当图片小于框时候，图片大小等于框大小，当大于框的时候，则成比例呈现
       	var viewWidth=_this.data.screenWidth;           //设置图片固定宽度值，  
        var	viewHeight=parseInt(viewWidth/ratio);    //计算的高度值
     	if (viewHeight< cnt_offeth) {
            viewHeight=cnt_offeth;
        }
        _this.setData({ 
            imgwidth:viewWidth,  
            imgheight:viewHeight,
            cnt_boxw:cnt_offetw,
            cnt_boxh:cnt_offeth,
        })
    },
    startEvent:function(e){
    	//1.获取鼠标点击下去的
    	this.setData({
	     	startx: e.touches[0].pageX,
	      	starty: e.touches[0].pageY
	    })
    },
    moveEvent: function(e) { 
		var _this=this;
		//2.鼠标移动的位置
		var pageX = e.touches[0].pageX;
		var pageY = e.touches[0].pageY;	
		var x,y;
		//3.记住初始化图片x,y
		var endx=_this.data.x,endy=_this.data.y;
		//4.判断
		var w_x=_this.data.imgwidth-_this.data.cnt_boxw;//x拖拽值：图片宽-框的宽
		var h_y=parseInt(_this.data.imgheight-_this.data.cnt_boxh);//y拖拽值：图片高-框高
		var DistanceX = pageX - _this.data.startx;//x:当鼠标点击到移动的点之间的距离
		var DistanceY =pageY - _this.data.starty;//y:当鼠标点击到移动的点之间的距离
		if (DistanceX>0){
			//往右移动 如果当前的值大于等于0时则不移动，否则当前值加上鼠标拖拽的距离
			if (endx >= 0) {
		        x = 0;
		    } else {
		        x = endx + DistanceX;
		    }
	    }else{
	    	//往左移动:x拖拽值大于等于当前的值，说明已经到边上了，就等于拖拽值，否则当前的值加上鼠标拖拽的距离
			if (w_x >= endx) {
		        x = -w_x;
		    } else {
		        x = endx + DistanceX;
		    }
	    }
	    if (DistanceY>0){
	    	//往下移动:如果当前的值大于等于0时则不移动，否则当前值加上鼠标拖拽的距离
			if(endy>=0){
				y =0;
		    }else{
		        y = endy + DistanceY;
		    }
	    }else{
	    	//往上移动:y拖拽值大于等于当前的值，说明已经到边上了，就等于拖拽值，否则当前的值加上鼠标拖拽的距离
	    	if(-endy==h_y||-endy>h_y){
	    		y=-h_y;
	    		console.log("da0")
	    	}else{
	    		y=endy+DistanceY;
	    		console.log("da 1")
	    	}
	 	}
   		setTimeout(function() {
	      	_this.animation.translate(x, y).step();
			_this.setData({
	       		animationData: this.animation.export()
	   		})
	    }.bind(this), 0)

	    _this.setData({
	    	x:x,
	    	y:y,
	    }) 
	    endx=x;endy=y;//记住这次的图片移动的范围
	    _this.data.startx=pageX;_this.data.starty=pageY;// 每移动一次把上一次的点作为原点
    },
    endEvent:function(){
 		clearTimeout(function(){
    		this.animation.translate(this.data.x,this.data.y).step();
			this.setData({
	       		animationData: this.animation.export()
	   		})
     	});
    }
})