wxml部分

wxss部分

.container {
display: flex;
align-items: center;
justify-content: center;
width: 100%;
height: 100%;
}

.container image {
width: 686rpx;
height: 686rpx;
background-color: #f9f9f9;
}

.canvas-box {
position: fixed;
top: 999999rpx;
left: 0;
}

js部分(qr地址下载地址：https://github.com/demi520/wxapp-qrcode/blob/master/utils/qrcode.js)

var QR = require("…/…/js/qrcode.js");

Page({

/**

• 页面的初始数据
  */
  data: {
  timestart:0, //长按开始
  timeend:0, //长按结束
  canvasHidden: false, //canvas显示
  imagePath: ‘’, //图片路径
  },

/**

• 生命周期函数–监听页面加载
  */
  onLoad: function (options) {
  //option为上个页面传递过来的参数
  var jiaoyanCode = ‘9123546’;
  // if (options) {
  // jiaoyanCode = options.jiaoyanCode;
  // }
  console.log(jiaoyanCode);

var size = this.setCanvasSize(); //动态设置画布大小 
this.createQrCode(jiaoyanCode, "mycanvas", size.w, size.h);

},

//适配不同屏幕大小的canvas
setCanvasSize: function () {
var size = {};
try {
var res = wx.getSystemInfoSync();
var scale = 750 / 686; //不同屏幕下canvas的适配比例；设计稿是750宽 686是因为样式wxss文件中设置的大小
var width = res.windowWidth / scale;
var height = width; //canvas画布为正方形
size.w = width;
size.h = height;
} catch (e) {
// Do something when catch error
console.log(“获取设备信息失败” + e);
}
return size;
},

/**

• 绘制二维码图片
  */
  createQrCode: function (url, canvasId, cavW, cavH) {
  //调用插件中的draw方法，绘制二维码图片
  QR.api.draw(url, canvasId, cavW, cavH);
  setTimeout(() => {
  this.canvasToTempImage();
  }, 1000);
  },

/**

• 获取临时缓存照片路径，存入data中
  */
  canvasToTempImage: function () {
  var that = this;
  //把当前画布指定区域的内容导出生成指定大小的图片，并返回文件路径。
  wx.canvasToTempFilePath({
  canvasId: ‘mycanvas’,
  success: function (res) {
  console.log(res,“dadas”)
  var tempFilePath = res.tempFilePath;
  console.log(tempFilePath);
  that.setData({
  imagePath: tempFilePath,
  // canvasHidden:true
  });
  },
  fail: function (res) {
  console.log(res);
  }
  });
  },

/**

• 点击图片进行预览
  */
  previewImg: function (e) {
  var img = this.data.imagePath;
  console.log(img);
  wx.previewImage({
  current: img, // 当前显示图片的http链接
  urls: [img] // 需要预览的图片http链接列表
  });
  },
  //点击开始时的时间
  timestart: function (e) {
  var _this = this;
  _this.setData({ timestart: e.timeStamp });
  },

//点击结束的时间
timeend: function (e) {
var _this = this;
_this.setData({ timeend: e.timeStamp });
},
bingLongClick() {//长按事件 保存二维码
var _this = this;
var times = _this.data.timeend - _this.data.timestart;
if (times > 300) {
wx.saveImageToPhotosAlbum({
filePath: _this.data.imagePath,//返回的临时文件路径，下载后的文件会存储到一个临时文件
success: function (res) {
wx.showToast({
title: ‘保存成功’,
})
},
fail(res){
wx.showToast({
title: ‘保存失败请截屏’,
})
}
})
}
}
})