【发布时间】：2016-12-09 03:43:06
【问题描述】：
在我的开发系统（Win 10 Pro，VS 2015）上，我正在 VS 2015 中测试一个 Web 表单应用程序；它使用母版页。当我尝试显示调整大小后刚刚写入的文件中的照片时，asp 内容页面中的图像控件不显示任何内容，而它可以很好地显示原始照片。这是 cmets 中详述的问题的代码隐藏片段：
// During testing, sRelLoc contains "~/i/SlideShow/1th.jpg" (original photo)
string sRelLocMod = sRelLoc.Replace("~/", "").Replace("/", "\\");
// During testing, Global.sgHomeDir contains "K:\\DataAndDocs\\12_Projects\\TinyNP\\TinyNP\\"
string sImgUrl = Global.sgHomeDir + sRelLocMod;
// sImgUrl now contains
System.Drawing.Image Photo = null;
// Read original photo from file
using (FileStream fs = new FileStream(sImgUrl, FileMode.Open, FileAccess.Read))
{
Photo= System.Drawing.Image.FromStream(fs);
}
// ResizeImage from https://www.codeproject.com/articles/191424/resizing-an-image-on-the-fly-using-net
System.Drawing.Image PhotoResized = ResizeImage(Photo, new Size(400, 400), true);
sImgUrl = Global.sgHomeDir + "i\\tempImg.jpg";
using (FileStream fs = new FileStream(sImgUrl, FileMode.Open, FileAccess.Write))
{
PhotoResized.Save(fs,System.Drawing.Imaging.ImageFormat.Jpeg);
}
// NOTE THAT: The image has been saved correctly in its resized form inside the expected directory
sImgUrl = sImgUrl.Replace("\\", "/");
//sImgUrl now contains "K:/DataAndDocs/12_Projects/TinyNP/TinyNP/i/tempImg.jpg"
// Image1 is an Image control on an asp.net web page.
// PROBLEM: The following statement displays nothing where Image1 is
// placed (not even a red-x or anything) , ...
Image1.ImageUrl = sImgUrl;
// ... but displays the unresized original just fine when the following statement is used instead:
// Image1.ImageUrl = sRelLoc;
无论是否在调试模式下运行，行为都相同。
也许有比将调整大小的照片写入临时文件 tempImg.jpg 然后从中读取更好的方法？
在 jignesh 和 Sami 回复后更新：
我在 Default.aspx.cs 中使用 MapPath（请参阅下面的新 cmets）。
现在使用 System.Uri 将路径转换为以“file:///”开头的 Url。导致什么都没有显示。将“file:”替换为“http:”会导致显示损坏的图像符号。更新后的代码是：
// During testing, sRelLoc contains "~/i/SlideShow/1.jpg" (original photo)
string sRelLocMod = sRelLoc.Replace("~/", "").Replace("/", "\\");
// During testing, Global.sgHomeDir contains "K:\\DataAndDocs\\12_Projects\\TinyNP\\TinyNP"
// which was obtained in Default.aspx.cs Page Load Event by
// Global.sgHomeDir = HttpContext.Current.Server.MapPath(null);
string sImgPath = Global.sgHomeDir + "\\" + sRelLocMod;
// sImgPath now contains "K:\\DataAndDocs\\12_Projects\\TinyNP\\TinyNP\\i\\SlideShow\\1.jpg"
System.Drawing.Image Photo = null;
// Read original photo from file
using (FileStream fs = new FileStream(sImgPath, FileMode.Open, FileAccess.Read))
{ Photo= System.Drawing.Image.FromStream(fs); }
// ResizeImage from https://www.codeproject.com/articles/191424/resizing-an-image-on-the-fly-using-net
System.Drawing.Image PhotoResized = ResizeImage(Photo, new Size(400, 400), true);
sImgPath = Global.sgHomeDir + "\\i\\tempImg.jpg";
// sImgPath now contains "K:\\DataAndDocs\\12_Projects\\TinyNP\\TinyNP\\i\\tempImg.jpg"
using (FileStream fs = new FileStream(sImgPath, FileMode.OpenOrCreate, FileAccess.Write))
{ PhotoResized.Save(fs, System.Drawing.Imaging.ImageFormat.Jpeg); }
// I have verified that the image has been saved correctly in its resized form inside the expected directory
System.Uri ImgUrl = new System.Uri(sImgPath, UriKind.Absolute);
// Image1 is an Image control on an asp.net web page.
string sImgUrl = ImgUrl.ToString();
//sImgUrl now contains "file:///K:/DataAndDocs/12_Projects/TinyNP/TinyNP/i/tempImg.jpg"
Image1.ImageUrl = sImgUrl;
// The above statement DOES NOT work (displays nothing at all)
// However:
//Image1.ImageUrl = "~/i/tempImg.jpg"; // ** DOES ** work ok
// If I replace "file:" with "http:", a broken image symbol is displayed.
但有效的是使用波浪号“~”，即使它看起来不像 Url。可以使用波浪号吗？是否会给我带来任何麻烦，例如部署到托管服务器时？
【问题讨论】：
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因为浏览器无法访问您的磁盘。您必须给它一个 URL，而不是路径。也不要手动更改 URL 到路径，这就是
MapPath()的用途。