C#生成缩略图控件
2009-02-28 08:18:04 来源：WEB开发网4、 客户端浏览器得到这张图片。网页加载完成。
好，原理是说了不少，虽然我尽量写得通俗，但难免大家一时半会儿可能不好理解。那我现在就把代码贴出来让大家参考。
这个缩略图控件还没有添加水印等类似版权保护的功能，各位有兴趣的高手不妨完善一下这部分内容。同时与各位朋友相互学习，加强思考，增进思维。我们不管ASP.NET孰优孰劣，对于个人来说，既然追随ASP.NET，就要把ASP.NET用好，随波逐流的程序员永远不会优秀。
using System;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Drawing;
using System.ComponentModel;
using System.Drawing.Design;
using System.Drawing.Drawing2D;
using System.Text;
using System.IO;
namespace BlogLan.Web.Controls
{
/// <summary>
/// 缩略图控件。
/// </summary>
[DefaultProperty("ImageUrl")]
[ToolboxData("<{0}:Thumbnail runat=server></{0}:Thumbnail>")]
[DesignerAttribute(typeof(Designer.ThumbnailDesigner))]
[Description("缩略图控件。")]
public class Thumbnail : WebControl
{
public Thumbnail()
: base(HtmlTextWriterTag.Img)
{
this.Width = Unit.Parse("100");
this.Height = Unit.Parse("75");
}
//Private Members
private bool urlResolved;
/// <summary>
/// 获取或设置图片路径。
/// </summary>
[Editor("System.Web.UI.Design.ImageUrlEditor, System.Design, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a", typeof(UITypeEditor)), Description("获取或设置图片路径"), Bindable(true), Category("Appearance"), DefaultValue(""), UrlProperty]
public string ImageUrl
{
get
{
if (this.ViewState["ImageUrl"] != null)
{
return (string)this.ViewState["ImageUrl"];
}
return string.Empty;
}
set
{
this.ViewState["ImageUrl"] = value;
}
}
/// <summary>
/// 获取或设置Jpeg缩略图的质量，值范围-100。
/// </summary>
[DefaultValue(80)]
public int JpegQuality
{
get
{
if (this.ViewState["JpegQuility"] != null)
{
return (int)this.ViewState["JpegQuility"];
}
return 80;
}
set
{
if (value > 100)
{
this.ViewState["JpegQuility"] = 100;
}
else if (value < 20)
{
this.ViewState["JpegQuility"] = 20;
}
else
{
this.ViewState["JpegQuility"] = value;
}
}
}
[DefaultValue(typeof(Unit), "100px")]
public override Unit Width
{
get
{
return base.Width;
}
set
{
base.Width = value;
}
}
[DefaultValue(typeof(Unit), "75px")]
public override Unit Height
{
get
{
return base.Height;
}
set
{
base.Height = value;
}
}
internal bool UrlResolved
{
get
{
return this.urlResolved;
}
set
{
this.urlResolved = value;
}
}
/// <summary>
/// 获取或设置控件相对于网页上其他元素的对齐方式。
/// </summary>
[DefaultValue(ImageAlign.NotSet), Description("获取或设置控件相对于网页上其他元素的对齐方式。")]
public virtual ImageAlign ImageAlign
{
get
{
object obj2 = this.ViewState["ImageAlign"];
if (obj2 != null)
{
return (ImageAlign)obj2;
}
return ImageAlign.NotSet;
}
set
{
if ((value < ImageAlign.NotSet) || (value > ImageAlign.TextTop))
{
throw new ArgumentOutOfRangeException("value");
}
this.ViewState["ImageAlign"] = value;
}
}
/// <summary>
/// [禁用Enabled属性在任何位置编辑。]
/// </summary>
[Browsable(false), EditorBrowsable(EditorBrowsableState.Never)]
public override bool Enabled
{
get
{
return base.Enabled;
}
set
{
base.Enabled = value;
}
}
/// <summary>
/// 如无法显示图片时显示的替代文本。
/// </summary>
[DefaultValue(""), Bindable(true), Localizable(true), Description("如无法显示图片时显示的替代文本。")]
public virtual string AlternateText
{
get
{
if (this.ViewState["AlternateText"] != null)
{
return (string)this.ViewState["AlternateText"];
}
return string.Empty;
}
set
{
this.ViewState["AlternateText"] = value;
}
}
/// <summary>
/// 获取或设置一个值，该值指示控件是否生成空字符串值的替换文字属性。
/// </summary>
[DefaultValue(true), Description("获取或设置一个值，该值指示控件是否生成空字符串值的替换文字属性。")]
public virtual bool GenerateEmptyAlternateText
{
get
{
if (this.ViewState["GenerateEmptyAlternateText"] != null)
{
return (bool)this.ViewState["GenerateEmptyAlternateText"];
}
return true;
}
set
{
this.ViewState["GenerateEmptyAlternateText"] = value;
}
}
/// <summary>
/// 获取或设置图像详细说明的位置。
/// </summary>
[Editor("System.Web.UI.Design.UrlEditor, System.Design, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a", typeof(UITypeEditor)), UrlProperty, DefaultValue(""), Description("获取或设置图像详细说明的位置。")]
public virtual string DescriptionUrl
{
get
{
string str = (string)this.ViewState["DescriptionUrl"];
if (str != null)
{
return str;
}
return string.Empty;
}
set
{
this.ViewState["DescriptionUrl"] = value;
}
}
//Methods
/// <summary>
/// 重写AddAttributesToRender方法。
/// </summary>
/// <param name="writer"></param>
protected override void AddAttributesToRender(HtmlTextWriter writer)
{
if (string.IsNullOrEmpty(this.Page.Request["thumbnail"]))
{
this.AddThumbnailAttributesToRender(writer, string.Empty);
}
}
protected virtual internal void AddThumbnailAttributesToRender(HtmlTextWriter writer, string ForcedImageUrl)
{
base.AddAttributesToRender(writer);
string imageUrl = this.ImageUrl;
if (!this.UrlResolved)
{
imageUrl = base.ResolveClientUrl(imageUrl);
}
//在设计时强制赋予图形路径。
if (!string.IsNullOrEmpty(ForcedImageUrl))
{
imageUrl = ForcedImageUrl;
writer.AddAttribute(HtmlTextWriterAttribute.Src, imageUrl);
}
else
{
writer.AddAttribute(HtmlTextWriterAttribute.Src, this.Page.Request.Url.AbsolutePath + "?" + this.GetQueryString(), false);
}
imageUrl = this.DescriptionUrl;
if (imageUrl.Length != 0)
{
writer.AddAttribute(HtmlTextWriterAttribute.Longdesc, base.ResolveClientUrl(imageUrl));
}
imageUrl = this.AlternateText;
if ((imageUrl.Length > 0) || this.GenerateEmptyAlternateText)
{
writer.AddAttribute(HtmlTextWriterAttribute.Alt, imageUrl);
}
switch (this.ImageAlign)
{
case ImageAlign.Left:
writer.AddAttribute(HtmlTextWriterAttribute.Align, "left");
break;
case ImageAlign.Right:
writer.AddAttribute(HtmlTextWriterAttribute.Align, "right");
break;
case ImageAlign.Baseline:
writer.AddAttribute(HtmlTextWriterAttribute.Align, "baseline");
break;
case ImageAlign.Top:
writer.AddAttribute(HtmlTextWriterAttribute.Align, "top");
break;
case ImageAlign.Middle:
writer.AddAttribute(HtmlTextWriterAttribute.Align, "middle");
break;
case ImageAlign.Bottom:
writer.AddAttribute(HtmlTextWriterAttribute.Align, "bottom");
break;
case ImageAlign.AbsBottom:
writer.AddAttribute(HtmlTextWriterAttribute.Align, "absbottom");
break;
case ImageAlign.AbsMiddle:
writer.AddAttribute(HtmlTextWriterAttribute.Align, "absmiddle");
break;
case ImageAlign.NotSet:
break;
default:
writer.AddAttribute(HtmlTextWriterAttribute.Align, "texttop");
break;
}
if (this.BorderWidth.IsEmpty)
{
writer.AddStyleAttribute(HtmlTextWriterStyle.BorderWidth, "0px");
}
}
private string GetQueryString()
{
StringBuilder sb = new StringBuilder();
sb.Append("thumbnail=" + this.Page.Server.HtmlEncode(this.ImageUrl));
sb.Append("&w=" + this.Width.Value.ToString());
sb.Append("&h=" + this.Height.Value.ToString());
sb.Append("&bc=" + this.BackColor.ToArgb().ToString());
sb.Append("&jq=" + this.JpegQuality.ToString());
return sb.ToString();
}
protected override void RenderContents(HtmlTextWriter writer)
{
}
protected override ControlCollection CreateControlCollection()
{
return new EmptyControlCollection(this);
}
protected override void OnInit(EventArgs e)
{
base.OnInit(e);
this.Init += new EventHandler(Thumbnail_Init);
this.PreRender += new EventHandler(Thumbnail_PreRender);
}
void Thumbnail_PreRender(object sender, EventArgs e)
{
if (HttpContext.Current != null)
{
RenderThumbnailImage(this.Page.Request, this.Page.Response);
}
}
void Thumbnail_Init(object sender, EventArgs e)
{
if (HttpContext.Current != null)
{
RenderThumbnailImage(this.Page.Request, this.Page.Response);
}
}
static void RenderThumbnailImage(HttpRequest request, HttpResponse response)
{
if (string.IsNullOrEmpty(request["thumbnail"]))
{
return;
}
Thumbnail thumbnail = new Thumbnail();
Bitmap tmb;
try
{
thumbnail.ImageUrl = request["thumbnail"];
try
{
thumbnail.Width = Unit.Parse(request["w"]);
}
catch
{
thumbnail.Width = Unit.Pixel(100);
}
try
{
thumbnail.Height = Unit.Parse(request["h"]);
}
catch
{
thumbnail.Height = Unit.Pixel(75);
}
try
{
thumbnail.BackColor = Color.FromArgb(Convert.ToInt32(request["bc"]));
}
catch
{
thumbnail.BackColor = Color.Black;
}
try
{
thumbnail.JpegQuality = Convert.ToInt32(request["jq"]);
}
catch
{
thumbnail.JpegQuality = 80;
}
tmb = thumbnail.GetThumbnail();
}
catch
{
tmb = Properties.Resources.GenerateImageError;
}
response.Clear();
string[] ImageFilePart = thumbnail.ImageUrl.ToLower().Split('.');
string Suffix = "bmp";
if (ImageFilePart.Length > 1)
{
Suffix = ImageFilePart[ImageFilePart.Length - 1];
}
if (Suffix == "gif")
{
response.ContentType = "image/gif";
tmb.Save(response.OutputStream, System.Drawing.Imaging.ImageFormat.Gif);
}
else if (Suffix == "jpg" || Suffix == "jpeg")
{
response.ContentType = "image/jpeg";
System.Drawing.Imaging.EncoderParameters encoderParams = new System.Drawing.Imaging.EncoderParameters();
long[] quality = new long[] { Convert.ToInt64(thumbnail.JpegQuality) };
System.Drawing.Imaging.EncoderParameter encoderParam = new System.Drawing.Imaging.EncoderParameter(System.Drawing.Imaging.Encoder.Quality, quality);
encoderParams.Param[0] = encoderParam;
System.Drawing.Imaging.ImageCodecInfo[] arrayICI = System.Drawing.Imaging.ImageCodecInfo.GetImageEncoders();
System.Drawing.Imaging.ImageCodecInfo jpegICI = null;
for (int fwd = 0; fwd < arrayICI.Length - 1; fwd++)
{
if (arrayICI[fwd].FormatDescription.Equals("JPEG"))
{
jpegICI = arrayICI[fwd];
break;
}
}
if (jpegICI != null)
{
tmb.Save(response.OutputStream, jpegICI, encoderParams);
}
else
{
tmb.Save(response.OutputStream, System.Drawing.Imaging.ImageFormat.Jpeg);
}
}
else
{
response.ContentType = "image/bmp";
tmb.Save(response.OutputStream, System.Drawing.Imaging.ImageFormat.Bmp);
}
tmb.Dispose();
response.Flush();
}
//
public Bitmap GetThumbnail()
{
return this.GetThumbnail(this);
}
private Bitmap GetThumbnail(Thumbnail thumbnail)
{
if (thumbnail == null)
return Properties.Resources.GenerateImageError;
System.Drawing.Image OriginalImage;
try
{
if (thumbnail.DesignMode)
{
//string pagepath = thumbnail.MapPathSecure("/");
OriginalImage = (System.Drawing.Image)Properties.Resources.ThumbnailDesign;
}
else
{
OriginalImage = System.Drawing.Image.FromFile(thumbnail.Context.Server.MapPath(thumbnail.ImageUrl));
}
}
catch
{
return Properties.Resources.GenerateImageError;
}
Size thumbnailNewSize = this.GetNewSize(Convert.ToInt32(thumbnail.Width.Value), Convert.ToInt32(thumbnail.Height.Value), OriginalImage.Width, OriginalImage.Height);
Bitmap outbmp = new Bitmap(Convert.ToInt32(thumbnail.Width.Value), Convert.ToInt32(thumbnail.Height.Value));
Graphics g = Graphics.FromImage(outbmp);
try
{
g.CompositingQuality = CompositingQuality.HighQuality;
g.SmoothingMode = SmoothingMode.HighQuality;
g.InterpolationMode = InterpolationMode.HighQualityBicubic;
g.Clear(thumbnail.BackColor);
Rectangle _Vb_t_record_0 = new Rectangle((int)Math.Round((double)(((double)(thumbnail.Width.Value - thumbnailNewSize.Width)) / 2.0)), (int)Math.Round((double)(((double)(thumbnail.Height.Value - thumbnailNewSize.Height)) / 2.0)), thumbnailNewSize.Width, thumbnailNewSize.Height);
g.DrawImage(OriginalImage, _Vb_t_record_0, 0, 0, OriginalImage.Width, OriginalImage.Height, GraphicsUnit.Pixel);
g.Dispose();
}
catch
{
return Properties.Resources.GenerateImageError;
}
finally
{
g.Dispose();
OriginalImage.Dispose();
}
return outbmp;
}
private Size GetNewSize(int maxWidth, int maxHeight, int width, int height)
{
double w = 0.0;
double h = 0.0;
double sw = Convert.ToDouble(width);
double sh = Convert.ToDouble(height);
double mw = Convert.ToDouble(maxWidth);
double mh = Convert.ToDouble(maxHeight);
if ((sw < mw) & (sh < mh))
{
w = sw;
h = sh;
}
else if ((sw / sh) > (mw / mh))
{
w = maxWidth;
h = (w * sh) / sw;
}
else
{
h = maxHeight;
w = (h * sw) / sh;
}
return new Size(Convert.ToInt32(w), Convert.ToInt32(h));
}
}
}
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