【IT168技术文档】
自定义控件：广告内容后期加载。以及NamingContainer层次的应用，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，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，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; } } } }
