c# – 使用WebClient获取远程图像会产生粒状GIF,无法处理PNG BMP
问候!
我正在创建一个Web表单原型(ImageLaoder.aspx),它将返回一个图像,以便它可以像其他Web表单/网页的简单示例一样使用: <img src="http://www.mydomain.com/ImageLoader.aspx?i=http://images.mydomain.com/img/a.jpg" /> 到目前为止,它加载JPG没有问题,但是与原始数据相比,GIF看起来“颗粒状”,而BMP和PNG导致以下异常: System.Runtime.InteropServices.ExternalException:GDI中发生一般错误 到目前为止我的代码看起来像这样: protected void Page_Load(object sender,EventArgs e) { string l_filePath = Request.QueryString["i"]; System.Drawing.Image l_image = GetImage(l_filePath); if (l_image != null) { System.Drawing.Imaging.ImageFormat l_imageFormat = DetermineImageFormat(l_filePath); WriteImageAsReponse(l_image,l_imageFormat); } } private System.Drawing.Image GetImage(string filePath) { WebClient l_WebClient = new WebClient(); byte[] l_imageBytes = l_WebClient.DownloadData(filePath); System.Drawing.Image l_image = null; using (MemoryStream l_MemStream = new MemoryStream(l_imageBytes,l_imageBytes.Length)) { l_MemStream.Write(l_imageBytes,l_imageBytes.Length); l_image = System.Drawing.Image.FromStream(l_MemStream,true); l_MemStream.Close(); } return l_image; } private System.Drawing.Imaging.ImageFormat DetermineImageFormat(string filePath) { if (filePath.EndsWith(".jpg",StringComparison.OrdinalIgnoreCase)) return System.Drawing.Imaging.ImageFormat.Jpeg; else if (filePath.EndsWith(".gif",StringComparison.OrdinalIgnoreCase)) return System.Drawing.Imaging.ImageFormat.Gif; else if (filePath.EndsWith(".png",StringComparison.OrdinalIgnoreCase)) return System.Drawing.Imaging.ImageFormat.Png; else return System.Drawing.Imaging.ImageFormat.Bmp; } private void WriteImageAsReponse(System.Drawing.Image image,System.Drawing.Imaging.ImageFormat imageFormat) { if (image == null) return; System.Drawing.Bitmap l_outputBitMap = new Bitmap(image); if (imageFormat == System.Drawing.Imaging.ImageFormat.Jpeg) Response.ContentType = "image/jpg"; else if (imageFormat == System.Drawing.Imaging.ImageFormat.Gif) Response.ContentType = "image/gif"; else if (imageFormat == System.Drawing.Imaging.ImageFormat.Png) Response.ContentType = "image/png"; else Response.ContentType = "image/bmp"; l_outputBitMap.Save(Response.OutputStream,imageFormat); } 任何想法为什么GIF是颗粒状的,PNG和BMP导致异常? 解决方法
关于GetImage方法的几点:
>使用Image.FromStream时,不应关闭(或处置)流 简而言之,我相信您的GetImage方法可以替换为: private Image GetImage(string filePath) { WebClient l_WebClient = new WebClient(); byte[] l_imageBytes = l_WebClient.DownloadData(filePath); MemoryStream l_stream = new MemoryStream(l_imageBytes); return Image.FromStream(l_stream); } 现在,更重要的是 – 为什么要加载图像?为什么不将文件本身作为响应提供,设置内容类型就像你已经在做的那样 – 或者可能只是基于扩展名?换句话说,您的所有代码都将成为: protected void Page_Load(object sender,EventArgs e) { string filePath = Request.QueryString["i"]; string extension = l_filePath.Substring(l_filePath.LastIndexOf('.') + 1); Response.ContentType = "image/" + extension; byte[] data = new WebClient.DownloadData(filePath); Response.OutputStream.Write(data,data.Length); Response.End(); } 更多的错误处理(包括“这是一个合理的扩展吗?”)会很好,但除此之外我觉得没关系.实际加载图像的唯一好处是,您可以验证它确实是图像而不是病毒或类似的东西. 编辑:只是出于兴趣,你有充分的理由为什么你想要图像请求通过你的服务器?为什么网页作者会写: <img src="http://www.mydomain.com/ImageLoader.aspx?i=http://images.mydomain.com/img/a.jpg" /> 代替 <img src="http://images.mydomain.com/img/a.jpg" /> 有一些原因可能会有用,但在许多情况下,这只是一种浪费. (编辑:李大同) 【声明】本站内容均来自网络,其相关言论仅代表作者个人观点,不代表本站立场。若无意侵犯到您的权利,请及时与联系站长删除相关内容! |