C# 数字验证码设计

设计步骤

（1）创建Windows应用程序项目，在窗体Form1上添加一个标签和一个按钮；一个文本框控件和一个图片框控件pictureBox。

（2）编写代码

 public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }
        private string str_ValidateCode;
        //生成任意长度的字符串
        public string GetRandomNumberString(int int_NumberLength)
        {
            string str_Number = string.Empty; //表示空字符串。此字段为只读。
            Random theRandomNumber = new Random();
            for(int int_index=0;int_index<int_NumberLength;int_index++)
            {
                str_Number += theRandomNumber.Next(10).ToString();
            }
            return str_Number;
        }
        //生成验证码的随机颜色
        public Color GetRandomColor()
        {
            Random RandomNum_First = new Random((int)DateTime.Now.Ticks);
            //对于C#的随机数，没什么好说的
            System.Threading.Thread.Sleep(RandomNum_First.Next(50));
            Random RandomNum_Second = new Random((int)DateTime.Now.Ticks);
            //为了在白色背景上显示，尽量生成深色
            int int_Red = RandomNum_First.Next(256);
            int int_Green = RandomNum_Second.Next(256);
            int int_Blue = (int_Red + int_Green > 400) ? 0 : 400 - int_Red - int_Green;
            int_Blue = (int_Blue > 255) ? 255 : int_Blue;
            return Color.FromArgb(int_Red, int_Green, int_Blue);
        }
        //根据字符串生成图像
        public void CreateImage(string str_ValidateCode)
        {
            int int_ImageWidth = str_ValidateCode.Length *13;
            Random newRandom = new Random();
            //图高20px
            Bitmap theBitmap = new Bitmap(int_ImageWidth, 20);
            Graphics theGraphics = Graphics.FromImage(theBitmap);
            //白色背景
            theGraphics.Clear(Color.White);
            //灰色边框
            theGraphics.DrawRectangle(new Pen(Color.LightGray, 1), 0, 0, int_ImageWidth - 1, 19);
            //10pt字体
            Font theFont = new Font("Arial", 10);
            for(int int_index=0;int_index<str_ValidateCode.Length;int_index++)
            {
                string str_char = str_ValidateCode.Substring(int_index,1);
                Brush newBrush = new SolidBrush(GetRandomColor());
                Point thePos = new Point(int_index * 13 + 1 + newRandom.Next(3), 1 + newRandom.Next(3));
                theGraphics.DrawString(str_char, theFont, newBrush, thePos);
            }
            //将生成的图片显示在图片框中
            pictureBox1.Image = theBitmap;          
        }

        private void Form1_Load(object sender, EventArgs e)
        {
            //4位数字验证码
            str_ValidateCode = GetRandomNumberString(4);
            CreateImage(str_ValidateCode);
        }

        private void button1_Click(object sender, EventArgs e)
        {
            if(str_ValidateCode==textBox1.Text)
            {
                MessageBox.Show("验证通过");
            }
            else
            {
                MessageBox.Show("验证失败，请再输入一次");
            }
        }
    }