绘制微信小程序验证码功能的实例代码

1.在 utils 文件中新建 mcaptcha.js 文件，写入以下代码：

module.exports = class Mcaptcha {
  //画板
 constructor(options) {
  this.options = options;
  this.fontSize = options.height * 3 / 4;
  this.init();
  this.refresh(this.options.code);
 }
 init() {
  this.ctx = wx.createCanvasContext(this.options.el);
  this.ctx.setTextBaseline("middle");
  this.ctx.setFillStyle(this.randomColor(180, 240));
  this.ctx.fillRect(0, 0, this.options.width, this.options.height);
 }
  //绘制彩图
 refresh(code) {
  let arr = (code + '').split('');
  let width = this.options.width;
  let height = this.options.height;
  let ctx = this.ctx;
  if (arr.length === 0) {
   arr = ['e', 'r', 'r','o','r'];
  };
  let offsetLeft = width * 0.6 / (arr.length - 1);
  let marginLeft = width * 0.2;
  arr.forEach((item, index) => {
   ctx.setFillStyle(this.randomColor(0, 180));
   let size = this.randomNum(24, this.fontSize);
   ctx.setFontSize(size);
   let dis = offsetLeft * index + marginLeft - size * 0.3;
   let deg = this.randomNum(-30, 30);
   ctx.translate(dis, height*0.5);
   ctx.rotate(deg * Math.PI / 180);
   ctx.fillText(item, 0, 0);
   ctx.rotate(-deg * Math.PI / 180);
   ctx.translate(-dis, -height * 0.5);
  })
  //绘制干扰线
  for (var i = 0; i < 2; i++) {
	  ctx.strokeStyle = this.randomColor(40, 180);
	  ctx.beginPath();
	  ctx.moveTo(this.randomNum(0, width), this.randomNum(0, height));
	  ctx.lineTo(this.randomNum(20, width), this.randomNum(2, height));
	  ctx.stroke();
  }
  //绘制干扰点
  for (var i = 0; i < 30; i++) {
	  ctx.fillStyle = this.randomColor(0, 255);
	  ctx.beginPath();
	  ctx.arc(this.randomNum(0, width), this.randomNum(0, height), 1, 0, 2 * Math.PI);
	  ctx.fill();
	 }
  ctx.draw();
 }
  //设置随机数的颜色
 randomNum(min, max) {
  return Math.floor(Math.random() * (max - min) + min);
 }
 randomColor(min, max) {
  let r = this.randomNum(min, max);
  let g = this.randomNum(min, max);
  let b = this.randomNum(min, max);
  return "rgb(" + r + "," + g + "," + b + ")";
 }
}

2.在需要验证码的js文件中引入

let Mcaptcha = require("../../../utils/mcaptcha.js");

res.data 是要传到mcaptcha.js 中的 code 值，也就是验证码，可以随意写为如：“ho55”，“a2sd” 等等。我这里是从后台传过来的数据，（前人写的代码，不好改动，只在前端加上干扰线和彩图）。

new Mcaptcha({
  el: 'canvas',
  width: 100,
  height: 30,
  code: res.data
});

wxml 文件， bindtap="getImgYZM" 是 new Mcaptcha 的方法名，再次点击可以换验证码图片。

<view bindtap="getImgYZM" class="yzm">
  <canvas style="width:{{cvs.width}};height:{{cvs.height}};" canvas-id="canvas"></canvas>
</view>

如果是在前端设置随机数，可以在data:{} 里面写

 data: {
   str:"0,1,2,3,4,5,6,7,8,9,A,B,C,D,E,F,G,H,I,J,K,L,M,N,P,Q,R,S,T,U,V,W,X,Y,Z",
   randStr:""
 }
//获取随机数
var res = "";
for(var i = 0; i < str.length ; i ++) {
  var id = Math.ceil(Math.random()*35);
  res += chars[id];
}
return res;

这一步可不看，以下是后端C#语言产生随机数返给前端的代码：

using JobClass;
using System;
using System.Collections.Generic;
using System.Drawing;
using System.Linq;
using System.Web;
using System.Web.SessionState;

namespace WebSite.pcode
{
  /// <summary>
  /// getcode 的摘要说明
  /// </summary>
  public class getcode : IHttpHandler, IRequiresSessionState
  {
    public void ProcessRequest(HttpContext context)
    {
      context.Response.ContentType = "text/plain";
      string str = "0,1,2,3,4,5,6,7,8,9,A,B,C,D,E,F,G,H,I,J,K,L,M,N,P,Q,R,S,T,U,V,W,X,Y,Z";
      string randStr = "";
      //生成随机数 Random
      Random randobj = new Random();
      string[] arr = str.Split(',');
      for (int i = 0; i < 4; i++)
      {
        randStr += arr[randobj.Next(arr.Length)];
      }
      context.Response.Write(randStr);
      return;
    }
    public bool IsReusable
    {
      get
      {
        return false;
      }
    }
  }
}

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