C# WINFORM 動態驗證碼實現

1.隨機產生字串
2.隨機設定字串的顯示
3.每隔一秒字串顯示變化
4點擊驗證碼，會產生新的驗碼

String str = "";//全域變數
        Random r = new Random();//全域對象
        private void pictureBox1_Click(object sender, EventArgs e)//點擊驗證碼，會產生新的驗碼
        {
            str = null;
            for (int i = 0; i < 5; i++) {
                int rn = r.Next(0, 10);
                str += rn;
            }
           
        }
        private void timer1_Tick(object sender, EventArgs e)//計時器當中去實現。
        {
            Bitmap bmp = new Bitmap(120, 120);
            Graphics g = Graphics.FromImage(bmp);
            for (int i = 0; i < 5; i++)
            {
                String[] fonts = { "微軟雅黑", "宋體", "黑體", "隸書", "仿宋" };//隨機設定字型的樣式
                Point p = new Point(i * 15, 0);
                Color[] colors = { Color.Red, Color.Pink, Color.Black, Color.Gray, Color.GreenYellow };//隨機設定字型的顏色
                g.DrawString(str[i].ToString(), new Font(fonts[r.Next(0, 5)], 20, FontStyle.Bold), new SolidBrush(colors[r.Next(0, 5)]), p);//畫圖
            }
            for (int i = 0; i < 100;i++ )//畫出聲燥線
            {
                Point p1 = new Point(r.Next(0, bmp.Width), r.Next(0, bmp.Height));
                Point p2 = new Point(r.Next(0, bmp.Width), r.Next(0, bmp.Height));
                g.DrawLine(new Pen(Brushes.Green), p1, p2);
            }
            pictureBox1.Image = bmp;
        }
        private void Form1_Load(object sender, EventArgs e)//啟動計時器
        {
            timer1.Start();
            for (int i = 0; i < 5; i++)
            {
                int rn = r.Next(0, 10);
                str += rn;
            }
        }