static List<Brush> CaptchaBrushes = null;
public static FileStreamResult CreateCaptcha(string captcha)
{
if (CaptchaBrushes == null)
{
CaptchaBrushes = new List<Brush>();
CaptchaBrushes.Add(Brushes.White);
CaptchaBrushes.Add(Brushes.Gold);
CaptchaBrushes.Add(Brushes.LightSkyBlue);
CaptchaBrushes.Add(Brushes.LimeGreen);
CaptchaBrushes.Add(Brushes.AliceBlue);
CaptchaBrushes.Add(Brushes.AntiqueWhite);
CaptchaBrushes.Add(Brushes.BurlyWood);
CaptchaBrushes.Add(Brushes.Silver);
}
int width = 90;
int height = 45;
//https://stackoverflow.com/questions/61365732/cannot-access-a-closed-stream-when-returning-filestreamresult-from-c-sharp-netc
//Using statements close and unload the variable from memory set in the using statement which is why you are getting an error trying to access a closed memory stream.You don't need to use a using statement if you are just going to return the result at the end.
//這個 memory stream 不用關閉或 dispose
var ms = new MemoryStream();
// 釋放所有在 GDI+ 所佔用的記憶體空間 ( 非常重要!! )
using (Bitmap _bmp = new Bitmap(width, height))
using (Graphics _graphics = Graphics.FromImage(_bmp))
using (Font _font = new Font("Courier New", 24, FontStyle.Bold)) // _font 設定要出現在圖片上的文字字型、大小與樣式
{
// (封裝 GDI+ 繪圖介面) 所有繪圖作業都需透過 Graphics 物件進行操作
_graphics.Clear(Color.Black);
// 如果想啟用「反鋸齒」功能，可以將以下這行取消註解
//_graphics.TextRenderingHint = TextRenderingHint.AntiAlias;
// 將亂碼字串「繪製」到之前產生的 Graphics 「繪圖板」上
var x = 10;
for(var i = 0; i < captcha.Length; i++)
{
_graphics.DrawString(captcha.Substring(i, 1), _font, CaptchaBrushes[Su.MathUtil.GetRandomInt(CaptchaBrushes.Count)], x, Su.MathUtil.GetRandomInt(15));
x += 10 + Su.MathUtil.GetRandomInt(10);
}
// 畫線
_graphics.DrawLine(new Pen(CaptchaBrushes[Su.MathUtil.GetRandomInt(CaptchaBrushes.Count)], 1),
Su.MathUtil.GetRandomInt(0, Convert.ToInt32((width * 0.9 / 2))), 0, Su.MathUtil.GetRandomInt(Convert.ToInt32(width / 2), Convert.ToInt32(width * 1.9 / 2)), height);
_graphics.DrawLine(new Pen(CaptchaBrushes[Su.MathUtil.GetRandomInt(CaptchaBrushes.Count)], 1),
Su.MathUtil.GetRandomInt(Convert.ToInt32(width / 2), Convert.ToInt32(width * 1.9 / 2)), 0, Su.MathUtil.GetRandomInt(0, Convert.ToInt32((width * 0.9 / 2))), height);
_graphics.DrawLine(new Pen(CaptchaBrushes[Su.MathUtil.GetRandomInt(CaptchaBrushes.Count)], 1),
0,
Su.MathUtil.GetRandomInt(height / 2),
width,
height / 2 + Su.MathUtil.GetRandomInt(height / 2)
);
_graphics.DrawLine(new Pen(CaptchaBrushes[Su.MathUtil.GetRandomInt(CaptchaBrushes.Count)], 1),
0,
height / 2 + Su.MathUtil.GetRandomInt(height / 2),
width,
Su.MathUtil.GetRandomInt(height / 2)
);
_bmp.Save(ms, System.Drawing.Imaging.ImageFormat.Jpeg);
}
ms.Seek(0, SeekOrigin.Begin);
// Controller 的型別為 FileResult
return new FileStreamResult(ms, "image/jpeg")
{ FileDownloadName = $"{DateTime.Now.Ymdhmsf()}.jpg" };
}
輸出用的 Controller 和 Action 如下:
namespace Web.Controllers
{
public class CaptchaController : Controller
{
[Route("captcha")]
public async Task<FileStreamResult> Index()
{
//產生 Captcha 並存入 Session 之中。目前是四位數字
string captcha = (await Ah.ReGetAsync<object>("api/kol/create-captcha-code")).ToString();
//產生圖檔並回傳 FileStreamResult
return Su.Wu.CreateCaptcha(captcha);
}
}
}