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asp.net验证码图片生成示例

2017年12月12日  | 移动技术网IT编程  | 我要评论

桃花依旧笑春风全文,乔邵恒,奥巴马微博

验证码是一张图片。我们需要在前台代码中写一段<img>，src指向一张页面（validateimage.aspx）。

复制代码 代码如下:

<script language="javascript">

        function changeimg() {
            $("#imgcheckno").attr("src", "validateimage.aspx?r=" + getrandom(999));
        }
        function getrandom(n) { return math.floor(math.random() * n + 1) }
</script>

<div>
<img id="imgcheckno" src="validateimage.aspx" style="border-color: #000000; border-width: 1px;border-style: solid">
 <span onclick="changeimg();">看不清?换一张</span>
 </div>
<div>
   <div class="labelcss">验证码：</div>
<div>
<asp:textbox id="tbxcheckno" runat="server" cssclass="tbxcss"></asp:textbox>
</div>
<div>
<asp:button id="btnsubmit" runat="server" text="立即注册" onclick="btnsubmit_click" />
</div>

validateimage.aspx 用来生产验证码图片，并将验证码的码值保存到cookie中。
代码如下：

复制代码 代码如下:

public partial class validateimage : system.web.ui.page
    {
        protected void page_load(object sender, eventargs e)
        {
            this.createcheckcodeimage(rndnum());
        }

        /// <summary>生成验证码
        /// </summary>
        /// <returns></returns>
        private string rndnum()
        {
            int number;
            char code;
            string checkcode = string.empty;

            system.random random = new random();

            for (int i = 0; i < 4; i++)
            {
                number = random.next();
                if (number % 2 == 0)
                    code = (char)('0' + (char)(number % 10));
                else
                    code = (char)('a' + (char)(number % 26));
                checkcode += code.tostring();
            }
            response.cookies.add(new httpcookie("yzmcode", checkcode));
            return checkcode;
        }

        /// <summary>向页面生成验证码gif图片
        /// </summary>
        /// <param name="checkcode"></param>
        private void createcheckcodeimage(string checkcode)
        {
            if (checkcode == null || checkcode.trim() == string.empty)
                return;
            system.drawing.bitmap image = new system.drawing.bitmap((int)math.ceiling((checkcode.length * 12.5)), 22);
            graphics g = graphics.fromimage(image);
            try
            {
                //生成随机生成器
                random random = new random();
                //清空图片背景色
                g.clear(color.white);
                //画图片的背景噪音线
                for (int i = 0; i < 25; i++)
                {
                    int x1 = random.next(image.width);
                    int x2 = random.next(image.width);
                    int y1 = random.next(image.height);
                    int y2 = random.next(image.height);
                    g.drawline(new pen(color.silver), x1, y1, x2, y2);
                }

                font font = new system.drawing.font("arial", 12, (system.drawing.fontstyle.bold | system.drawing.fontstyle.italic));
                system.drawing.drawing2d.lineargradientbrush brush = new system.drawing.drawing2d.lineargradientbrush(new rectangle(0, 0, image.width, image.height), color.blue, color.darkred, 1.2f, true);
                g.drawstring(checkcode, font, brush, 2, 2);
                //画图片的前景噪音点
                for (int i = 0; i < 100; i++)
                {
                    int x = random.next(image.width);
                    int y = random.next(image.height);
                    image.setpixel(x, y, color.fromargb(random.next()));
                }
                //画图片的边框线
                g.drawrectangle(new pen(color.silver), 0, 0, image.width - 1, image.height - 1);
                system.io.memorystream ms = new system.io.memorystream();
                image.save(ms, system.drawing.imaging.imageformat.gif);
                response.clearcontent();
                response.contenttype = "image/gif";
                response.binarywrite(ms.toarray());
            }
            finally
            {
                g.dispose();
                image.dispose();
            }
        }

    }

最后就是后台事件，判断当前验证码是否正确。
代码如下：

复制代码 代码如下:

#region 页面控件事件
        protected void btnsubmit_click(object sender, eventargs e)
        {
            if (string.compare(request.cookies["yzmcode"].value, tbxcheckno.text, true) != 0)
            {
                response.write("<script>alert('验证码错误!')</script>");
            }
            else
            {
               // response.write("<script>alert('验证吗正确!!!')</script>");
            }
        }
  #endregion

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