今天就跟大家聊聊有关Asp.net mvc中怎么实时生成缩率图，可能很多人都不太了解，为了让大家更加了解，小编给大家总结了以下内容，希望大家根据这篇文章可以有所收获。
思路很简单，就是根据请求，判断需要的缩率图是否已存在于硬盘上，如果有直接返回，没有则下载原图，并生成缩率图到本地，返回给客户端。
下面直接粘贴代码片段：
/// <summary>
/// 生成图片缩率图Action
/// </summary>
/// <param name="p">原图url</param>
/// <param name="id">图片尺寸以及生成缩率图的类型</param>
/// <returns></returns>
[ValidateInput(false)]
public ActionResult Index(string p, string id)
{
if (string.IsNullOrEmpty(p))
{
return new HttpStatusCodeResult(404);
}
string oPath = Regex.Replace(p, @"http[s]?://(.*?)/", "/", RegexOptions.IgnoreCase);
int? oWidth = 200, oHeight = 200;
int cutMode = 3;
string pPath;
string oDir;
if (!string.IsNullOrEmpty(id))
{
string[] ss = id.Split(new char[] { '_' }, StringSplitOptions.RemoveEmptyEntries);
if (ss.Length < 2)
{
return new HttpStatusCodeResult(404);
}
if (ss.Length > 2)
{
cutMode = int.Parse(ss[2]);
}
oPath = oPath.Insert(oPath.LastIndexOf('/') + 1, string.Format("{0}_{1}_{2}_", ss[0], ss[1], cutMode));
oWidth = int.Parse(ss[0]);
oHeight = int.Parse(ss[1]);
}
pPath = Server.MapPath(oPath);
oDir = Path.GetDirectoryName(pPath);
if (!System.IO.File.Exists(pPath))
{
byte[] imagebytes = FileHelper.DownLoadFile(p);
if (!Directory.Exists(oDir))
{
Directory.CreateDirectory(oDir);
}
FileHelper.MakeThumbnail(FileHelper.BytToImg(imagebytes), oWidth.Value, oHeight.Value, (ThumbnailMode)cutMode, pPath, true);
}
return File(pPath, FileHelper.GetContentTypeByExtension(Path.GetExtension(pPath).ToLower()));
}辅助方法：
public class FileHelper
{
/// <summary>
/// 图片后缀和ContentType对应字典
/// </summary>
static Dictionary<string, string> extensionContentTypeDic;
static FileHelper()
{
if (extensionContentTypeDic == null)
{
//.jpg", ".png", ".gif", ".jpeg
extensionContentTypeDic = new Dictionary<string, string>();
extensionContentTypeDic.Add(".jpg", "image/jpeg");
extensionContentTypeDic.Add(".png", "image/png");
extensionContentTypeDic.Add(".gif", "image/gif");
extensionContentTypeDic.Add(".jpeg", "image/jpeg");
}
}
/// <summary>
/// 根据后缀名获取extension
/// </summary>
/// <param name="extension"></param>
/// <returns></returns>
public static string GetContentTypeByExtension(string extension)
{
if (extensionContentTypeDic.ContainsKey(extension))
{
return extensionContentTypeDic[extension];
}
return null;
}
/// <summary >
/// 将Image对象转化成二进制流
/// </summary >
/// <param name="image" > </param >
/// <returns > </returns >
public static byte[] ImageToByteArray(Image image)
{
MemoryStream imageStream = new MemoryStream();
Bitmap bmp = new Bitmap(image.Width, image.Height);
Graphics g = Graphics.FromImage(bmp);
g.DrawImage(image, new System.Drawing.Rectangle(0, 0, image.Width, image.Height));
try
{
bmp.Save(imageStream, image.RawFormat);
}
catch (Exception e)
{
bmp.Save(imageStream, System.Drawing.Imaging.ImageFormat.Jpeg);
}
byte[] byteImg = imageStream.GetBuffer();
bmp.Dispose();
g.Dispose();
imageStream.Close();
return byteImg;
}
/// <summary>
/// 字节流转换成图片
/// </summary>
/// <param name="byt">要转换的字节流</param>
/// <returns>转换得到的Image对象</returns>
public static Image BytToImg(byte[] byt)
{
MemoryStream ms = new MemoryStream(byt);
Image img = Image.FromStream(ms);
ms.Close();
return img;
}
/// <summary>
/// 生成缩率图
/// </summary>
/// <param name="originalImage">原始图片Image</param>
/// <param name="width">缩率图宽</param>
/// <param name="height">缩率图高</param>
/// <param name="mode">生成缩率图的方式</param>
/// <param name="thumbnailPath">缩率图存放的地址</param>
public static Image MakeThumbnail(Image originalImage, int width, int height, ThumbnailMode mode, string thumbnailPath, bool isSave = true)
{
int towidth = width;
int toheight = height;
int x = 0;
int y = 0;
int ow = originalImage.Width;
int oh = originalImage.Height;
switch (mode)
{
case ThumbnailMode.HW://指定高宽缩放（可能变形）
break;
case ThumbnailMode.W://指定宽，高按比例
toheight = originalImage.Height * width / originalImage.Width;
break;
case ThumbnailMode.H://指定高，宽按比例
towidth = originalImage.Width * height / originalImage.Height;
break;
case ThumbnailMode.Cut://指定高宽裁减（不变形）
if ((double)originalImage.Width / (double)originalImage.Height > (double)towidth / (double)toheight)
{
oh = originalImage.Height;
ow = originalImage.Height * towidth / toheight;
y = 0;
x = (originalImage.Width - ow) / 2;
}
else
{
ow = originalImage.Width;
oh = originalImage.Width * height / towidth;
x = 0;
y = (originalImage.Height - oh) / 2;
}
break;
default:
break;
}
//新建一个bmp图片
System.Drawing.Image bitmap = new System.Drawing.Bitmap(towidth, toheight);
//新建一个画板
Graphics g = System.Drawing.Graphics.FromImage(bitmap);
//设置高质量插值法
g.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.High;
//设置高质量,低速度呈现平滑程度
g.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality;
//清空画布并以透明背景色填充
g.Clear(Color.Transparent);
//在指定位置并且按指定大小绘制原图片的指定部分
g.DrawImage(originalImage, new Rectangle(0, 0, towidth, toheight),
new Rectangle(x, y, ow, oh),
GraphicsUnit.Pixel);
if (!isSave)
{
return bitmap;
}
try
{
//以jpg格式保存缩略图
//bitmap.Save(thumbnailPath, bitmap.RawFormat);
bitmap.Save(thumbnailPath, ImageFormat.Jpeg);
return bitmap;
}
catch (System.Exception e)
{
throw e;
}
finally
{
originalImage.Dispose();
bitmap.Dispose();
g.Dispose();
}
return null;
}
/// <summary>
/// 下载指定文件
/// </summary>
/// <param name="remoteUrl"></param>
/// <param name="ss"></param>
public static byte[] DownLoadFile(string remoteUrl)
{
WebClient wc = new WebClient();
try
{
return wc.DownloadData(remoteUrl);
}
catch (Exception e)
{
throw new Exception("下载文件失败");
}
}
}
public enum ThumbnailMode
{
/// <summary>
/// 指定高宽缩放（可能变形）
/// </summary>
HW,
/// <summary>
/// 指定高，宽按比例
/// </summary>
H,
/// <summary>
/// 指定宽，高按比例
/// </summary>
W,
/// <summary>
/// 指定高宽裁减（不变形）
/// </summary>
Cut,
}访问方式：
http://www.souji8.com/Home/Index/{width}_{height}_{ThumMode}?p={imageUrl}
{imageUrl}:目标图片地址
{ThumMode}: 1:指定高宽按比例、2：指定宽，高按比例、3：指定高宽裁减（不变形）
{Width}:期望图片宽
{Height}:期望图片高
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