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一、手势事件

下面二维码是一个实例dome，可扫码直接查看:

在ios系统中，系统自带了gesture事件，两个手指操作的时候，就会产生一下三种手势事件：

gesturestart：当一个手指已经按在屏幕上，另一个手指又触摸屏幕的时候触发。
gesturechange：当触摸屏幕的任何一个手指的位置发生变化的时候触发。
gestureend：当任何一个手指从屏幕上面移开时触发。

这里通过js自定义事件模仿ios的手势事件为Android添加相同的功能；

实现基本思路

在Android中我们可以监听touchstart、touchmove、touchend去实现手势事件的监听，
当触发touch事件的时候，会生成一个TouchEvent对象，我们可通过其属性e.touches.length来判断是否多点触控，通过e.touches[index].pageX,e.touches[index].pageY获取去触点坐标，通过e.target获取dom节点；

实现方法

1、创建自定义事件

var gesturestart = new CustomEvent('gesturestart');
var gesturechange = new CustomEvent('gesturechange');
var gestureend = new CustomEvent('gestureend');

1、gesturestart

首先定义两个变量存储触发状态和起始点信息

var istouch = false;
ar start = [];

监听touchstart事件，通过e.touches.length>2判断是否多点触控，如果是，触发自定义事件gesturestart

document.addEventListener("touchstart", function(e) {
    if(e.touches.length >= 2) { //判断是否有两个点在屏幕上
        istouch = true;
        start = e.touches; //得到第一组两个点
        e.target.dispatchEvent(gesturestart);
    };
}, false);

2、gesturechange

gesturechange事件中我们需在事件对象中返回以下两个属性：

• scale：表示两个手指之间的距离情况，向内收缩会缩短距离，这个值从1开始，并随距离拉大而增长
• rotation：表示手指变化引起的旋转角度，负值表示逆时针，正值表示顺时针，从零开始。
  对于两点间的距离我们可由以下公式计算

（1）缩放比例可通过两组点之间的长度比计算

　　　　scale =  dis1   /   dis2
      首先编写方法两点之间距离的方法（勾股定理）

function getDistance(p1, p2) {
    var x = p2.pageX - p1.pageX,
        y = p2.pageY - p1.pageY;
    return Math.sqrt((x * x) + (y * y));
};

（2）对于旋转角度第一组点的夹角与第二组点的夹角相减得到

　　　　deg= deg2-deg1 =arctan (x2-x1/y2-y1) – arctan (x4-x3/y4-y3) 　

编写获取夹角方法（反三角函数求夹角，注意弧度转化为角度）

function getAngle(p1, p2) {
    var x = p1.pageX - p2.pageX,
        y = p1.pageY - p2.pageY;
    return Math.atan2(y, x) * 180 / Math.PI;
};

监听touchmove事件，通过e.touches.length >= 2和istouch判断是否触发gesturechange事件

document.addEventListener("touchmove", function(e) {
    e.preventDefault();
    if(e.touches.length >= 2 && istouch) {
        var now = e.touches; //得到第二组触点
        var scale = getDistance(now[0], now[1]) / getDistance(start[0], start[1]); //得到缩放比例
        var rotation = getAngle(now[0], now[1]) - getAngle(start[0], start[1]); //得到旋转角度
        gesturechange.scale = scale.toFixed(2);
        gesturechange.rotation = rotation.toFixed(2);
        e.target.dispatchEvent(gesturechange);  
    };
}, false);

3、gestureend

监听touchend事件，通过istouch判断是否触发gestureend 事件

document.addEventListener("touchend", function(e) {
    if(istouch) {
        istouch = false;
        e.target.dispatchEvent(gestureend);
    };
}, false);

4、系统环境判断

function isAndroid(p1, p2) {
    var u = navigator.userAgent;
    return u.indexOf('Android') > -1 || u.indexOf('Adr') > -1; //是否android终端
};

封装以上方法并执行，即可实现安卓端与ios的手势事件兼容

完整代码见https://github.com/pangyongsheng/pangyongsheng.github.io/tree/master/gesture

^[1]: 部分代码参考https://blog.csdn.net/qq_17757973/article/details/54604625