简单验证码

许多网站都会有验证码输入。今天就写个简单验证码控件，新建一个固定图片作为画布，在画布画上随机的4个字符，保存图片。用pictureBox控件装载该图片

效果图：

外面调用CreateYZM()方法生成验证码，Code属性获取验证码的值，用于验证判断使用

每点击验证码，都会重新生成

代码如下：

//验证码
        public string Code { get;private set; }
        //验证码长度
        private int length = 4;


        //是否有噪点
        private bool hasZaoDian = true;
        public bool HasZaoDian { get; set; }

        string str = "asdfghjklzxcvbnmqwertyuiopQWERTYUIOPLKJHGFDSAZXCVBNM1234567890";
        Random rd = new Random();
        public void CreateYZM()
        { 
           Bitmap image =new Bitmap(65,23);
           Graphics gc =  Graphics.FromImage(image);
           gc.Clear(Color.YellowGreen);
           char[] codeChar = str.ToCharArray();
           int index = 0;
           StringBuilder code = new StringBuilder();
           for ( int i = 0 ; i < length ;i++ )
           {
              index = rd.Next(0,str.Length);
              code.Append(codeChar[index].ToString());
           }
           Code = code.ToString();
           gc.DrawString(code.ToString() , new Font("Couriew New" , 14f , FontStyle.Bold) , new SolidBrush(Color.Red) , new PointF(2 , 1));
           if ( hasZaoDian )  //是否画噪点，默认yes
           {
               for ( int i = 0 ; i < 80 ; i++ )
               {
                   int x = rd.Next(image.Width);
                   int y = rd.Next(image.Height);
                   image.SetPixel(x , y , Color.FromArgb(rd.Next()));
               }
           }
           pictureBox1.Image = image;
           gc.Dispose();
        }

        private void pictureBox1_Click(object sender , EventArgs e)
        {
            CreateYZM();
        }