Community Server专题六：Delegates & Events
在分析CSHttpModule.cs的时候，你会看到这样两句代码：
CSEvents.UserKnown(csContext.User);
CSEvents.CSException(csException);
其实短短两行代码后面隐藏了Delegates与Events的大量运用，CS也通过这样的运用实现了一种模块化的处理机制，即CSModules。
打开CommunityServerWeb项目下的communityserver.config文件，这是CS的配置文件(与Web.config不同，communityserver.config主要配置的是CS内部的一些运行机制，而Web.config主要配置的是与Asp.net的交互)。找到文件中的这段：
<CSModules>
<add name = "CSMembershipRulesModule" type = "CommunityServer.Components.CSMembershipRulesModule, CommunityServer.Components" />
<add name = "CSCatastrophicExceptionModule" type = "CommunityServer.Components.CSCatastrophicExceptionModule, CommunityServer.Components" />
<add name = "CSExceptionModule" type = "CommunityServer.Components.CSExceptionModule, CommunityServer.Components" />
<add name = "IrcCommands" type = "CommunityServer.Discussions.Components.IrcCommandsModule, CommunityServer.Discussions" />
<add name = "ForumCensorship" type = "CommunityServer.Discussions.Components.CensorshipModule, CommunityServer.Discussions" />
<add name = "ForumEmoticon" type = "CommunityServer.Discussions.Components.EmoticonModule, CommunityServer.Discussions" />
<add name = "ForumSourceCode" type = "CommunityServer.Discussions.Components.SourceCodeModule, CommunityServer.Discussions" />
<add name = "ForumHtmlScrubbing" type = "CommunityServer.Discussions.Components.HtmlScrubbingModule, CommunityServer.Discussions" />
<add name = "BBcodeToHtml" type = "CommunityServer.Discussions.Components.BBcodeToHtmlModule, CommunityServer.Discussions" />
<add name = "ForumPlainText" type = "CommunityServer.Discussions.Components.PlainTextModule, CommunityServer.Discussions" />
<add name = "WeblogCensorModule" type = "CommunityServer.Blogs.Components.CensorModule, CommunityServer.Blogs" />
<add name = "WeblogPostandArticleHtmlScrubbing" type = "CommunityServer.Blogs.Components.PostandArticleHtmlScrubbing, CommunityServer.Blogs" />
<add name = "WeblogFeedbackHtmlFormatting" type = "CommunityServer.Blogs.Components.FeedbackHtmlFormatting, CommunityServer.Blogs" />
<add name = "TrackbackModule" type = "CommunityServer.Blogs.Components.TrackbackModule, CommunityServer.Blogs" />
<add name = "XmlRpcPingModule" type = "CommunityServer.Blogs.Components.XmlRpcPingModule, CommunityServer.Blogs" />
<add name = "WeblogFormattingModule" type = "CommunityServer.Blogs.Components.WeblogFormattingModule, CommunityServer.Blogs" />
<add name = "PictureCensor" type = "CommunityServer.Galleries.Components.CensorPictureModule, CommunityServer.Galleries" />
<add name = "PictureHtmlScrubber" type = "CommunityServer.Galleries.Components.HtmlScrubberModule, CommunityServer.Galleries" />
<add name = "PictureComments" type = "CommunityServer.Galleries.Components.CommentModule, CommunityServer.Galleries" />
<!-- <add name = "MaxPictureSize" type = "CommunityServer.Galleries.Components.MaxPictureSizeModule, CommunityServer.Galleries" maxWidth="1024" maxHeight="768" quality="90" /> -->
</CSModules>
我们拿出其中的一个来分析运行过程，例：
<add name = "CSExceptionModule" type = "CommunityServer.Components.CSExceptionModule, CommunityServer.Components" />
这是CS中异常处理的模块，当发生异常的时候该模块将调用一个RedirectToMessage方法，提示一个友好的错误界面，告诉请求的用户有错误发生。那么CS系统是如何在发生错误的时候自动调用RedirectToMessage方法转向另外一个页面提示友好错误的呢？先打开CommunityServerComponents项目下Components文件夹中的CSApplication.cs
using System;
using System.Collections;
using System.ComponentModel;
using System.Web.Caching;
using System.Xml;
using CommunityServer.Configuration;
namespace CommunityServer.Components
{
#region Delegates
//Do we want one single delegate or a custom one for each type
//public delegate void CSEventHandler(object sender, CSEventArgs e);
public delegate void CSUserEventHandler(User user, CSEventArgs e);
public delegate void CSPostEventHandler(Post post, CSEventArgs e);
public delegate void CSSectionEventHandler(Section section, CSEventArgs e);
public delegate void CSGroupEventHandler(Group group, CSEventArgs e);
public delegate void CSExceptionHandler(CSException csEx, CSEventArgs e);
#endregion
/// <summary>
/// Summary description for CSApplication.
/// </summary>
public class CSApplication
{
#region private members
private EventHandlerList Events = new EventHandlerList();
private static readonly object sync = new object();
private Hashtable modules = new Hashtable();
#endregion
#region Event Keys (static)
private static object EventAuthorizePost = new object();
private static object EventPrePostUpdate = new object();
private static object EventPreProcessPost = new object();
private static object EventPostPostUpdate = new object();
private static object EventRatePost = new object();
//private static object EventPreRenderPost = new object();
private static object EventPreUserUpdate = new object();
private static object EventPostUserUpdate = new object();
private static object EventUserRemove = new object();
private static object EventUserKnown = new object();
private static object EventUserValidated = new object();
private static object EventPreSectionUpdate = new object();
private static object EventPostSectionUpdate = new object();
private static object EventPreSectionGroupUpdate = new object();
private static object EventPostSectionGroupUpdate = new object();
private static object EventUnhandledException = new object();
#endregion
#region cnstr
private CSApplication()
{
}
internal static CSApplication Instance()
{
const string key = "CSApplication";
CSApplication app = CSCache.Get(key) as CSApplication;
if(app == null)
{
lock(sync)
{
app = CSCache.Get(key) as CSApplication;
if(app == null)
{
CSConfiguration config = CSContext.Current.Config;
XmlNode node = config.GetConfigSection("CommunityServer/CSModules");
app = new CSApplication();
if(node != null)
{
foreach(XmlNode n in node.ChildNodes)
{
if(n.NodeType != XmlNodeType.Comment)
{
switch(n.Name)
{
case "clear":
app.modules.Clear();
break;
case "remove":
app.modules.Remove(n.Attributes["name"].Value);
break;
case "add":
string name = n.Attributes["name"].Value;
string itype = n.Attributes["type"].Value;
Type type = Type.GetType(itype);
if(type == null)
throw new Exception(itype + " does not exist");
ICSModule mod = Activator.CreateInstance(type) as ICSModule;
if(mod == null)
throw new Exception(itype + " does not implement ICSModule or is not configured correctly");
mod.Init(app, n);
app.modules.Add(name,mod);
break;
}
}
}
}
CacheDependency dep = new CacheDependency(null, new string[]{CSConfiguration.CacheKey});
CSCache.Max(key, app,dep);
}
}
}
return app;
}
#endregion
#region Post Events
#region Execute Events
internal void ExecuteAuthorizePost()
{
ExecuteUserEvent(EventAuthorizePost,CSContext.Current.User);
}
internal void ExecutePrePostEvents(Post post, ObjectState state, ApplicationType appType)
{
ExecutePostEvent(EventPreProcessPost,post,state,appType);
}
internal void ExecutePrePostUpdateEvents(Post post, ObjectState state, ApplicationType appType)
{
ExecutePostEvent(EventPrePostUpdate,post,state,appType);
}
internal void ExecutePostPostUpdateEvents(Post post, ObjectState state, ApplicationType appType)
{
ExecutePostEvent(EventPostPostUpdate,post,state,appType);
}
internal void ExecuteRatePostEvents(Post post, ApplicationType appType)
{
ExecutePostEvent(EventRatePost,post,ObjectState.None,appType);
}
// internal void ExecutePrePostRender(Post post, ApplicationType appType)
// {
// ExecutePostEvent(EventPreRenderPost,post,ObjectState.None,appType);
// }
protected void ExecutePostEvent(object EventKey, Post post,ObjectState state, ApplicationType appType)
{
CSPostEventHandler handler = Events[EventKey] as CSPostEventHandler;
if (handler != null)
{
handler(post, new CSEventArgs(state,appType));
}
}
#endregion
#region Events
/// <summary>
/// Event raised before a user accesses a page which can be used to create content
/// </summary>
public event CSUserEventHandler AuthorizePost
{
add{Events.AddHandler(EventAuthorizePost, value);}
remove{Events.RemoveHandler(EventAuthorizePost, value);}
}
/// <summary>
/// Event raised before any post processing takes place
/// </summary>
public event CSPostEventHandler PreProcessPost
{
add{Events.AddHandler(EventPreProcessPost, value);}
remove{Events.RemoveHandler(EventPreProcessPost, value);}
}
/// <summary>
/// Fires after PreProcessPost but before the post change is commited to the datastore
/// </summary>
public event CSPostEventHandler PrePostUpdate
{
add{Events.AddHandler(EventPrePostUpdate, value);}
remove{Events.RemoveHandler(EventPrePostUpdate, value);}
}
/// <summary>
/// Fires after a post change is commited to the datastore
/// </summary>
public event CSPostEventHandler PostPostUpdate
{
add{Events.AddHandler(EventPostPostUpdate, value);}
remove{Events.RemoveHandler(EventPostPostUpdate, value);}
}
/// <summary>
/// Fires after a Post or Thread is rated
/// </summary>
public event CSPostEventHandler RatePost
{
add{Events.AddHandler(EventRatePost, value);}
remove{Events.RemoveHandler(EventRatePost, value);}
}
// /// <summary>
// /// Event raised before an individual post is rendered
// /// </summary>
// public event CSPostEventHandler PreRenderPost
// {
// add{Events.AddHandler(EventPreRenderPost, value);}
// remove{Events.RemoveHandler(EventPreRenderPost, value);}
// }
#endregion
#endregion
#region User Events
#region Execute Events
internal void ExecuteUserValidated(User user)
{
ExecuteUserEvent(EventUserValidated,user);
}
internal void ExecuteUserKnown(User user)
{
ExecuteUserEvent(EventUserKnown,user);
}
internal void ExecutePreUserUpdate(User user, ObjectState state)
{
ExecuteUserEvent(EventPreUserUpdate,user,state,ApplicationType.Unknown);
}
internal void ExecutePostUserUpdate(User user, ObjectState state)
{
ExecuteUserEvent(EventPostUserUpdate,user,state,ApplicationType.Unknown);
}
internal void ExecuteUserRemove(User user)
{
ExecuteUserEvent(EventUserRemove,user,ObjectState.Delete,ApplicationType.Unknown);
}
protected void ExecuteUserEvent(object EventKey, User user)
{
ExecuteUserEvent(EventKey,user,ObjectState.None,ApplicationType.Unknown);
}
protected void ExecuteUserEvent(object EventKey, User user,ObjectState state, ApplicationType appType)
{
CSUserEventHandler handler = Events[EventKey] as CSUserEventHandler;
if (handler != null)
{
handler(user, new CSEventArgs(state,appType));
}
}
#endregion
#region Events
/// <summary>
/// Fires after a user's credentials have been validated.
/// </summary>
public event CSUserEventHandler UserValidated
{
add{Events.AddHandler(EventUserValidated, value);}
remove{Events.RemoveHandler(EventUserValidated, value);}
}
/// <summary>
/// Fires once the current user has been identified. This user may still be anonymous.
/// </summary>
public event CSUserEventHandler UserKnown
{
add{Events.AddHandler(EventUserKnown, value);}
remove{Events.RemoveHandler(EventUserKnown, value);}
}
/// <summary>
/// Fires before a User is saved/updated to the datastore
/// </summary>
public event CSUserEventHandler PreUserUpdate
{
add{Events.AddHandler(EventPreUserUpdate, value);}
remove{Events.RemoveHandler(EventPreUserUpdate, value);}
}
/// <summary>
/// Fires after a User is saved/updated to the datastore
/// </summary>
public event CSUserEventHandler PostUserUpdate
{
add{Events.AddHandler(EventPostUserUpdate, value);}
remove{Events.RemoveHandler(EventPostUserUpdate, value);}
}
/// <summary>
/// Fires before a User is removed from the datastore.
/// </summary>
public event CSUserEventHandler UserRemove
{
add{Events.AddHandler(EventUserRemove, value);}
remove{Events.RemoveHandler(EventUserRemove, value);}
}
#endregion
#endregion
#region Section Events
internal void ExecutePreSectionUpdate(Section section, ObjectState state, ApplicationType appType)
{
CSSectionEventHandler handler = Events[EventPreSectionUpdate] as CSSectionEventHandler;
if (handler != null)
{
handler(section, new CSEventArgs(state,appType));
}
}
internal void ExecutePostSectionUpdate(Section section, ObjectState state, ApplicationType appType)
{
CSSectionEventHandler handler = Events[EventPostSectionUpdate] as CSSectionEventHandler;
if (handler != null)
{
handler(section, new CSEventArgs(state,appType));
}
}
/// <summary>
/// Event raised before a section change is committed to the datastore (create/update)
/// </summary>
public event CSSectionEventHandler PreSectionUpdate
{
add{Events.AddHandler(EventPreSectionUpdate, value);}
remove{Events.RemoveHandler(EventPreSectionUpdate, value);}
}
/// <summary>
/// Event raised after a section chage is committed to the data store
/// </summary>
public event CSSectionEventHandler PostSectionUpdate
{
add{Events.AddHandler(EventPostSectionUpdate, value);}
remove{Events.RemoveHandler(EventPostSectionUpdate, value);}
}
#endregion
#region Group Events
internal void ExecutePreSectionGroupUpdate(Group group, ObjectState state, ApplicationType appType)
{
CSGroupEventHandler handler = Events[EventPreSectionGroupUpdate] as CSGroupEventHandler;
if (handler != null)
{
handler(group, new CSEventArgs(state,appType));
}
}
internal void ExecutePostSectionGroupUpdate(Group group, ObjectState state, ApplicationType appType)
{
CSGroupEventHandler handler = Events[EventPostSectionGroupUpdate] as CSGroupEventHandler;
if (handler != null)
{
handler(group, new CSEventArgs(state,appType));
}
}
/// <summary>
/// Event raised before a group chage is committed to the datastore (create/update)
/// </summary>
public event CSGroupEventHandler PreSectionGroupUpdate
{
add{Events.AddHandler(EventPreSectionGroupUpdate, value);}
remove{Events.RemoveHandler(EventPreSectionGroupUpdate, value);}
}
/// <summary>
/// Event raised after a group chage is committed to the data store
/// </summary>
public event CSGroupEventHandler PostSectionGroupUpdate
{
add{Events.AddHandler(EventPostSectionGroupUpdate, value);}
remove{Events.RemoveHandler(EventPostSectionGroupUpdate, value);}
}
#endregion
#region Exceptions
/// <summary>
/// Event raised before a group chage is committed to the datastore (create/update)
/// </summary>
public event CSExceptionHandler CSException
{
add{Events.AddHandler(EventUnhandledException, value);}
remove{Events.RemoveHandler(EventUnhandledException, value);}
}
internal void ExecuteCSExcetion(CSException csEx)
{
CSExceptionHandler handler = Events[EventUnhandledException] as CSExceptionHandler;
if (handler != null)
{
handler(csEx,new CSEventArgs());
}
}
#endregion
}
}
文件太长，我们抓出关键的部分来分析：
public delegate void CSExceptionHandler(CSException csEx, CSEventArgs e);
这里先申明一个委托，相当于一个函数指针。在通俗一点理解它就是一个跑腿的，专管传递对象与对象间的调用信息。
接下来：
internal static CSApplication Instance()
{
const string key = "CSApplication";
CSApplication app = CSCache.Get(key) as CSApplication;
if(app == null)
{
lock(sync)
{
app = CSCache.Get(key) as CSApplication;
if(app == null)
{
CSConfiguration config = CSContext.Current.Config;
XmlNode node = config.GetConfigSection("CommunityServer/CSModules");
app = new CSApplication();
if(node != null)
{
foreach(XmlNode n in node.ChildNodes)
{
if(n.NodeType != XmlNodeType.Comment)
{
switch(n.Name)
{
case "clear":
app.modules.Clear();
break;
case "remove":
app.modules.Remove(n.Attributes["name"].Value);
break;
case "add":
string name = n.Attributes["name"].Value;
string itype = n.Attributes["type"].Value;
Type type = Type.GetType(itype);
if(type == null)
throw new Exception(itype + " does not exist");
ICSModule mod = Activator.CreateInstance(type) as ICSModule;
if(mod == null)
throw new Exception(itype + " does not implement ICSModule or is not configured correctly");
mod.Init(app, n);
app.modules.Add(name,mod);
break;
}
}
}
}
CacheDependency dep = new CacheDependency(null, new string[]{CSConfiguration.CacheKey});
CSCache.Max(key, app,dep);
}
}
}
return app;
}
这段很重要，通过读取communityserver.config文件的<CSModules>，初始化每个CSModule，注意，初始化后并且调用了这些CSModule中的Init方法。具体看看这些Module中的Init都做了什么，打开CommunityServerComponents项目下的Components文件夹中的CSExceptionModule.cs：
//------------------------------------------------------------------------------
// <copyright company="Telligent Systems">
// Copyright (c) Telligent Systems Corporation. All rights reserved.
// </copyright>
//------------------------------------------------------------------------------
using System;
using System.Web;
namespace CommunityServer.Components
{
/// <summary>
/// Summary description for CSExceptionModule.
/// </summary>
public class CSExceptionModule : ICSModule
{
public CSExceptionModule()
{
//
// TODO: Add constructor logic here
//
}
#region ICSModule Members
public void Init(CSApplication csa, System.Xml.XmlNode node)
{
csa.CSException +=new CSExceptionHandler(csa_CSException);
}
#endregion
private void csa_CSException(CSException csEx, CSEventArgs e)
{
CSContext csContext = CSContext.Current;
if (csEx.ExceptionType != CSExceptionType.UnknownError && csContext.IsWebRequest)
{
RedirectToMessage(csContext.Context, csEx);
}
}
private static void RedirectToMessage (HttpContext context, CSException exception)
{
if ((exception.InnerException != null) && ( exception.InnerException is CSException))
{
CSException inner = (CSException) exception.InnerException;
}
context.Response.Redirect(Globals.GetSiteUrls().Message( exception.ExceptionType ), true);
}
}
}
哈哈，原来在Init方法里把一个CSExceptionHandler委托添加到CSException事件上，这个委托指向csa_CSException方法，还是通俗点说：如果CSException这个事件发生了，CSExceptionHandler这个跑腿的委托就会马上告诉csa_CSException方法要他执行，如果事件没有被激发就什么也不做。
名词: event 关键字使您得以指定当代码中的某些“事件”发生时调用的委托。此委托可以有一个或多个关联的方法，当代码指示该事件已发生时将调用关联的方法。
那么这个CSException又是怎么回事？在哪里定义的？我们回到CSApplication.cs文件中，看样几行：
public event CSExceptionHandler CSException
{
add{Events.AddHandler(EventUnhandledException, value);}
remove{Events.RemoveHandler(EventUnhandledException, value);}
}
这里定义了一个CSException事件，而事件发生的时候只能用CSExceptionHandler这个委托来做跑腿的。其实CS中是把委托都存放在了一个EventHandlerList中，因此此处你可以看到add与remove, 这是访问器的声明，用于添加或移除客户代码中的事件处理程序，这样做的好处是公开大量的事件但不为每个事件分配字段，而是使用EventHandlerList存储这些事件实例。为了理解事件的调用执行过程，我们还必须看几个文件：CSEvents.cs、CSEventArgs.cs：
CSEventArgs.cs存储事件的数据，这个很好理解，它继承自EventArgs。当事件发生时CSEventArgs用来传递事件的信息，这里传递两个值：ObjectState与ApplicationType(可以在Enumerations文件夹下找到这两个枚举的内容)
CSEvents.cs这是对事件调用的一个包装器，看异常处理的包装：
public static void CSException(CSException csEx)
{
CSApplication.Instance().ExecuteCSExcetion(csEx);
}
这里先调用CSApplication.Instance()方法，实例化一个CSApplication对象，如果你是第一次调用Instance()方法，就实例化所有在<CSModules>中配置的类，并且调用他们的Init方法(在CSModules中配置的这些类，都实现了ICSModule接口，而这个接口要求继承他的类都具备Init方法)，执行Init方法的目的就是把委托添加到事件上，使委托指向的方法可以在事件触发的时候被调用。实例化后再调用ExecuteCSExcetion方法并且传递CSException的实例，ExecuteCSExcetion方法如下：
internal void ExecuteCSExcetion(CSException csEx)
{
CSExceptionHandler handler = Events[EventUnhandledException] as CSExceptionHandler;
if (handler != null)
{
handler(csEx,new CSEventArgs());
}
}
先通过对EventHandlerList索引访问，即Events[EventUnhandledException]，从列表中找到这个CSExceptionHandler事件，如果不为null就执行它。EventUnhandledException又是什么，其实这只是一个Key，用来标示存储的事件。
有必要总结一下，不然你会被这种调用来调用去的关系搞得一头雾水，
以异常处理为例：
1：在错误发生后，调用Application_OnError方法；
2：在方法的最后调用CSEvents.CSException(csException)；
3：进入CSEvents包装器，调用CSApplication.Instance().ExecuteCSExcetion(csEx);
4：执行CSApplication.Instance()方法，如果是第一次执行就根据communityserver.config文件中的配置，把所有的CSModules实例化，并且调用ICSModule接口类中的Init方法，然后缓存这些实例化的类(如果是第二次访问就从缓存中读取)。
5：在实现ICSModule接口的类中，如CSExceptionModule.cs，Init方法是给事件添加委托的过程，这个过程中实现了委托指向的一个或者多个方法与事件进行关联，异常处理的方法csa_CSException(CSException csEx, CSEventArgs e)就是在这里被关联到异常事件上的。
6:经过上面几步后，CS系统接着调用ExecuteCSExcetion方法，在ExecuteCSExcetion方触发了CSException事件
7：CSException事件被触发后，就执行事件中委托所指向的函数，这里是CSExceptionModule.cs文件中的private void csa_CSException(CSException csEx, CSEventArgs e)。
CS如此大量的使用Delegates与Events带来了什么，也许你会认为它这样是把问题复杂化，而且觉得这非常没有必要，完全可以在异常处理的最后调用处理方法即可，何必通过事件来回周转！最后说明一下这样做的重要性：
1：通过事件使调用方法者与方法本身隔离，如在CSHttpModule.cs文件中的Application_OnError方法触发CSEvents.CSException事件，而事件要做些什么处理，需要调用什么方法Application_OnError根本不知道。如果你要改变CSEvents.CSException事件处理方法的结构，甚至十处理方法的名称，Application_OnError也不需要改动，因为他根本不关心具体的实现，它的任务只是触发这个事件。
2：如果你想一个方法调用多个方法，普通的做法就是在方法中一次调用或者在方法中嵌套调用。这样做并不是一个好的设计模式，而事件可以通过委托调用多个委托指向的方法(在异常处理中只指向了一个方法，当然你可以指向任意N个方法)，而这种调用也是相互隔离的，被调用的方法并不致到谁调用它，而调用者也不关心它调用谁。
3：模块化，你的代码直接没有非常的多紧密联系，而是通过事件来通知处理方法，在CS中又加入了xml的配置文件，使得这样的模块化更突出，你设置可以把处理异常的类单独编译在一个dll中。
好处还有很多…