标签：des style blog http io color os ar for
WebControl派生自Control类，所以WebControl的呈现功能基于Control的呈现逻辑之上，但有了比较大的扩展。
首先，WebControl重写了Render(HtmlTextWriter writer)方法，将呈现的逻辑一分为三：RenderBeginTag()、RenderContents()、RenderEndTag()。WebControl的这种设计基于一种假设：每个WebControl最终生成一个HTML控件（当然这个HTML控件中可能还包含其他HTML子控件），所以WebControl的呈现过程就可分为：呈现开始标签、呈现标签中的内容和呈现结尾标签。
protected internal override void Render(HtmlTextWriter writer)
{ this.RenderBeginTag(writer); this.RenderContents(writer); this.RenderEndTag(writer);}
①呈现开始标签：
public virtual void RenderBeginTag(HtmlTextWriter writer)
{ this.AddAttributesToRender(writer); HtmlTextWriterTag htmlTextWriterTag = this.TagKey; if (htmlTextWriterTag != HtmlTextWriterTag.Unknown) {writer.RenderBeginTag(htmlTextWriterTag);
return;}
writer.RenderBeginTag(this.TagName);}
由上面的实现代码可知：RenderBeginTag()方法所生成的HTML标签是由WebControl.TagKey或WebControl.TagName属性决定的。
[Browsable(false), DesignerSerializationVisibility(DesignerSerializationVisibility.Hidden)]protected virtual HtmlTextWriterTag TagKey
{ [TargetedPatchingOptOut("Performance critical to inline across NGen image boundaries")]get
{return this.tagKey;
}
}
TagKey的类型为HtmlTextWriterTag 枚举，如果你的标签不在这个枚举中，则你需要把TagKey属性设为Unkown，并设置TagName属性，TagName属性为String类型，这意味着你可以将该属性设为任意值。
[Browsable(false), DesignerSerializationVisibility(DesignerSerializationVisibility.Hidden)]protected virtual string TagName
{get
{if (this.tagName == null && this.TagKey != HtmlTextWriterTag.Unknown)
{this.tagName = Enum.Format(typeof(HtmlTextWriterTag), this.TagKey, "G").ToLower(CultureInfo.InvariantCulture);
}
return this.tagName;
}
}
②呈现标签中的内容：
protected internal virtual void RenderContents(HtmlTextWriter writer)
{ base.Render(writer);}
③呈现结尾标签：
public virtual void RenderEndTag(HtmlTextWriter writer)
{writer.RenderEndTag();
}
到这里WebControl的呈现过程，都说完了，但有一个疑问是：最外围的HTML标签是怎么添加属性和样式属性的呢？
相信细心的同学一定发现在WebControl类RenderBeginTag()方法中第一行代码：
this.AddAttributesToRender(writer);故名思议就是添加属性到呈现内容，我们看下该方法的实现：
protected virtual void AddAttributesToRender(HtmlTextWriter writer)
{if (this.ID != null)
{ writer.AddAttribute(HtmlTextWriterAttribute.Id, this.ClientID);}
if (this._webControlFlags[4])
{string accessKey = this.AccessKey;
if (accessKey.Length > 0) {writer.AddAttribute(HtmlTextWriterAttribute.Accesskey, accessKey);
}
}
if (!this.Enabled)
{if (this.SupportsDisabledAttribute)
{ writer.AddAttribute(HtmlTextWriterAttribute.Disabled, "disabled");}
if (this.RenderingCompatibility >= VersionUtil.Framework40 && !string.IsNullOrEmpty(WebControl.DisabledCssClass))
{if (string.IsNullOrEmpty(this.CssClass))
{ this.ControlStyle.CssClass = WebControl.DisabledCssClass;}
else {this.ControlStyle.CssClass = WebControl.DisabledCssClass + " " + this.CssClass;
}
}
}
if (this._webControlFlags[16])
{int tabIndex = (int)this.TabIndex;
if (tabIndex != 0) {writer.AddAttribute(HtmlTextWriterAttribute.Tabindex, tabIndex.ToString(NumberFormatInfo.InvariantInfo));
}
}
if (this._webControlFlags[8])
{string toolTip = this.ToolTip;
if (toolTip.Length > 0) {writer.AddAttribute(HtmlTextWriterAttribute.Title, toolTip);
}
}
if (this.TagKey == HtmlTextWriterTag.Span || this.TagKey == HtmlTextWriterTag.A)
{ this.AddDisplayInlineBlockIfNeeded(writer);}
if (this.ControlStyleCreated && !this.ControlStyle.IsEmpty)
{this.ControlStyle.AddAttributesToRender(writer, this);
}
if (this.attrState != null)
{ AttributeCollection attributes = this.Attributes;IEnumerator enumerator = attributes.Keys.GetEnumerator();
while (enumerator.MoveNext()) {string text = (string)enumerator.Current;
writer.AddAttribute(text, attributes[text]);
}
}
}
首先，AddAttributesToRender()是一个虚方法，我们可以重写，又因为它在RenderBeginTag()开始时被调用，很显然我们可以将最外围的HTML标签添加属性和样式属性的逻辑在这里实现。其次，我们注意到WebControl类实现RenderBeginTag()方法时完成了（例如：Enabled与否，不同呈现）等基本的功能。所以在我们重写该方法为外围标签添加自定义属性和样式属性时，为了获得WebControl提供的基本功能。需在派生的控件类中调用父类的该方法：
protected override void AddAttributesToRender(HtmlTextWriter writer)
{ base.AddAttributesToRender(writer); //......添加所需属性和样式的代码}
using System;using System.Collections.Generic;using System.ComponentModel;using System.Linq;using System.Text;using System.Web;using System.Web.UI;using System.Web.UI.WebControls;namespace CustomServerControls{public class Albumn : WebControl
{ //（一）：WebControl默认TagKey为span，这里重写为Divprotected override HtmlTextWriterTag TagKey
{get
{ return HtmlTextWriterTag.Div;}
}
//（二：）为主标签（Div）添加一些样式属性protected override void AddAttributesToRender(HtmlTextWriter writer)
{ base.AddAttributesToRender(writer); writer.AddStyleAttribute(HtmlTextWriterStyle.TextAlign, "center"); writer.AddStyleAttribute(HtmlTextWriterStyle.Width, "194px"); writer.AddStyleAttribute(HtmlTextWriterStyle.Height, "194px");writer.AddStyleAttribute("background", "url(Images/background.gif) no-repeat left");
}
//（三）：主标签的内容项是一个Img标签protected override void RenderContents(HtmlTextWriter writer)
{ writer.AddAttribute(HtmlTextWriterAttribute.Src, "Images/nature.jpg"); writer.AddAttribute(HtmlTextWriterAttribute.Width, "160px"); writer.AddAttribute(HtmlTextWriterAttribute.Height,"160px"); writer.AddStyleAttribute(HtmlTextWriterStyle.BorderStyle, "none"); writer.AddStyleAttribute(HtmlTextWriterStyle.Padding, "0px"); writer.AddStyleAttribute(HtmlTextWriterStyle.MarginTop, "16px");writer.RenderBeginTag(HtmlTextWriterTag.Img);
writer.RenderEndTag();
}
}
}
标签：des style blog http io color os ar for
原文地址：http://www.cnblogs.com/hanzhaoxin/p/4055422.html
