在开发中，有时候生成验证码的场景目前还是存在的，本篇演示不依赖第三方组件，生成随机验证码图片。
先添加验证码接口
public interface ICaptcha { /// <summary> /// 生成随机验证码 /// </summary> /// <param name="codeLength"></param> /// <returns></returns> Task<string> GenerateRandomCaptchaAsync(int codeLength = 4); /// <summary> /// 生成验证码图片 /// </summary> /// <param name="captchaCode">验证码</param> /// <param name="width">宽为0将根据验证码长度自动匹配合适宽度</param> /// <param name="height">高</param> /// <returns></returns> Task<CaptchaResult> GenerateCaptchaImageAsync(string captchaCode, int width = 0, int height = 30); }验证码返回模型
public class CaptchaResult { /// <summary> /// CaptchaCode /// </summary> public string CaptchaCode { get; set; } /// <summary> /// CaptchaMemoryStream /// </summary> public MemoryStream CaptchaMemoryStream { get; set; } /// <summary> /// Timestamp /// </summary> public DateTime Timestamp { get; set; } }接下来实现接口，主要是依赖微软的System.Drawing.Common组件，注意命名空间的引用
using System; using System.Drawing; using System.Drawing.Imaging; using System.IO; using System.Threading.Tasks; ... public class Captcha : ICaptcha { private const string Letters = "1,2,3,4,5,6,7,8,9,A,B,C,D,E,F,G,H,J,K,L,M,N,P,Q,R,S,T,U,V,W,X,Y,Z"; public Task<CaptchaResult> GenerateCaptchaImageAsync(string captchaCode, int width = 0, int height = 30) { //验证码颜色集合 Color[] c = { Color.Black, Color.Red, Color.DarkBlue, Color.Green, Color.Orange, Color.Brown, Color.DarkCyan, Color.Purple }; //验证码字体集合 string[] fonts = { "Verdana", "Microsoft Sans Serif", "Comic Sans MS", "Arial" }; //定义图像的大小，生成图像的实例 var image = new Bitmap(width == 0 ? captchaCode.Length * 25 : width, height); var g = Graphics.FromImage(image); //背景设为白色 g.Clear(Color.White); var random = new Random(); for (var i = 0; i < 100; i++) { var x = random.Next(image.Width); var y = random.Next(image.Height); g.DrawRectangle(new Pen(Color.LightGray, 0), x, y, 1, 1); } //验证码绘制在g中 for (var i = 0; i < captchaCode.Length; i++) { //随机颜色索引值 var cindex = random.Next(c.Length); //随机字体索引值 var findex = random.Next(fonts.Length); //字体 var f = new Font(fonts[findex], 15, FontStyle.Bold); //颜色 Brush b = new SolidBrush(c[cindex]); var ii = 4; if ((i + 1) % 2 == 0) ii = 2; //绘制一个验证字符 g.DrawString(captchaCode.Substring(i, 1), f, b, 17 + (i * 17), ii); } var ms = new MemoryStream(); image.Save(ms, ImageFormat.Png); g.Dispose(); image.Dispose(); return Task.FromResult(new CaptchaResult { CaptchaCode = captchaCode, CaptchaMemoryStream = ms, Timestamp = DateTime.Now }); } public Task<string> GenerateRandomCaptchaAsync(int codeLength = 4) { var array = Letters.Split(new[] { ',' }); var random = new Random(); var temp = -1; var captcheCode = string.Empty; for (int i = 0; i < codeLength; i++) { if (temp != -1) random = new Random(i * temp * unchecked((int)DateTime.Now.Ticks)); var index = random.Next(array.Length); if (temp != -1 && temp == index) return GenerateRandomCaptchaAsync(codeLength); temp = index; captcheCode += array[index]; } return Task.FromResult(captcheCode); } }在控制器中注入调用
using Microsoft.AspNetCore.Mvc; using System.Threading.Tasks; [Route("api/[controller]")] [ApiController] public class CaptchaController : ControllerBase { [HttpGet] public async Task<FileContentResult> CaptchaAsync([FromServices] ICaptcha _captcha) { var code = await _captcha.GenerateRandomCaptchaAsync(); var result = await _captcha.GenerateCaptchaImageAsync(code); return File(result.CaptchaMemoryStream.ToArray(), "image/png"); } }实际使用的时候，code就是本次生成的验证码，可以将其保存在session中，进行验证，或者其它方式。
