《转》http://www.pin5i.com/showtopic-11037.html
网站上的广告内容可能会因加载过慢而导致整个网页加载过慢，我们可以考虑将广告内全部放在网页最底部，等整个页面加载完毕後再采用javascript使其显示，考虑给控件一个TargetContainerID标识，控件广告内容将要被显示的容器ID，然后从控件自己所处的 开始向上查找该ID所指定的控件，(我们只向上找而没有向下找，并且没有处理某层次的子NamingContainer,所以不一定能够找到，这里没有考虑从Page对象向下递归查找主要考虑为了提高性能),如果没有找到，则考虑给用户一个事件让用户自己处理TargetContainer。
下面的自定义控件对此实现了封装:
namespace HBZ.Ads.Controls
{
using System;
using System.ComponentModel;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using HBZ.Ads;
using System.Collections.Generic;
using System.Text;
[Designer( typeof( HBZ.Ads.Controls.AdRotatorDesigner ) )]
public class AdRotator : WebControl
{
private Dictionary<string , Control> findControlHelperCacheList = new Dictionary<string , Control>( );
private readonly string scriptFormat = "var {0}_target = document.getElementById(\"{0}\"); var {1}_base = document.getElementById(\"{1}\"); if ({0}_target) {{ {0}_target.innerHTML = {1}_base.innerHTML; {1}_base.innerHTML = \"\"; }}";
private static readonly object eventObj = new object( );
public event FindTargetContainerEventHandler FindTargetContainer
{
add
{
Events.AddHandler( eventObj , value );
}
remove
{
Events.RemoveHandler( eventObj , value );
}
}
public AdRotator( )
: base( HtmlTextWriterTag.Span )
{
}
[TypeConverter( typeof( ValidatedControlConverter ) )]
[DefaultValue( "" ) , Category( "Data" ) , Description( "广告位后期加载后显示的位置的控件ID" )]
[IDReferenceProperty]
public string TargetContainerID
{
get
{
return (string)this.ViewState[ "TargetContainerID" ] ?? string.Empty;
}
set
{
this.ViewState[ "TargetContainerID" ] = value;
}
}
[Bindable( true ) , Category( "Data" ) , DefaultValue( "" ) , Description( "广告位的默认内容" )]
public string DefaultContent
{
get
{
return (string)this.ViewState[ "DefaultContent" ] ?? "广告位招租";
}
set
{
this.ViewState[ "DefaultContent" ] = value;
}
}
protected override void OnPreRender( EventArgs e )
{
base.OnPreRender( e );
if ( !string.IsNullOrEmpty( TargetContainerID ) )
{
this.Style.Add( HtmlTextWriterStyle.Display , "none" );
ClientScriptManager cs = Page.ClientScript;
if ( !cs.IsStartupScriptRegistered( this.ClientID ) )
{
cs.RegisterStartupScript( this.GetType( ) , this.ClientID , GetLazyLoadingScript( ) , true );
}
}
}
protected virtual string GetLazyLoadingScript( )
{
Control target = FindControlHelper( TargetContainerID );
if ( target == null )
{
throw new TargetContainerNotFoundException( );
}
StringBuilder sb = new StringBuilder( );
sb.AppendFormat( scriptFormat , target.ClientID , this.ClientID );
return sb.ToString( );
}
protected virtual void RenderAdvertisement( Advertisement ad , HtmlTextWriter writer )
{
// 广告内容
}
protected override void RenderContents( HtmlTextWriter writer )
{
// call RenderAdvertisement method
}
protected Control FindControlHelper( string id )
{
Control c = null;
if ( findControlHelperCacheList.ContainsKey( id ) )
{
c = findControlHelperCacheList[ id ];
}
else
{
c = base.FindControl( id ); // 注意：我们从自己开始向上沿NamingContainer层次查找
Control nc = NamingContainer;
while ( ( null == c ) && ( null != nc ) )
{
c = nc.FindControl( id );
nc = nc.NamingContainer;
}
if ( null == c )
{
// 因为我们是从自己开始向上沿NamingContainer层次查找，而没有向下找，
// 并且没有找每一层NamingContainer内的其他NamingContainer,
// 所以这种查找有可能出现没有找到id对应的控件
// 当没此时有找到时，激发FindTargetContainer事件交给用户自己设定Target Container Control
FindTargetContainerEventArgs args = new FindTargetContainerEventArgs( id );
OnFindTargetContainer( args );
c = args.Control;
}
if ( null != c )
{
findControlHelperCacheList[ id ] = c;
}
}
return c;
}
protected virtual void OnFindTargetContainer( FindTargetContainerEventArgs e )
{
FindTargetContainerEventHandler hander = Events[ eventObj ] as FindTargetContainerEventHandler;
if ( hander != null )
{
hander( this , e );
}
}
}
public delegate void FindTargetContainerEventHandler( object src , FindTargetContainerEventArgs e );
public class FindTargetContainerEventArgs : EventArgs
{
private string controlID;
private Control control;
public FindTargetContainerEventArgs( string controlId )
{
controlID = controlId;
}
public string ControlID
{
get
{
return controlID;
}
}
public Control Control
{
get
{
return control;
}
set
{
control = value;
}
}
}
public class TargetContainerNotFoundException : Exception
{
string exceptionMessage = string.Empty;
public TargetContainerNotFoundException( )
: this( "TargetContainerID所指定的控件没有找到！您或许应该处理一下FindTargetContainer事件" )
{
}
public TargetContainerNotFoundException( string message )
: base( message )
{
this.exceptionMessage = message;
}
public override string Message
{
get
{
if ( exceptionMessage != null )
{
return exceptionMessage;
}
return base.Message;
}
}
}
}
http://www.cn-web.com/cnweb/0/411/article/
看不懂的话，先看下asp.net中的NamingContainer详解
文章来源(WEB开发技术知识库)：http://www.cn-web.com/cnweb/0/411/article/
