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20190211

ref:
https://stackoverflow.com/questions/2340572/what-is-the-purpose-of-global-asax-in-asp-net


Global asax events explained
Application_Init: 
  Fired when an application initializes or is first called. It's invoked for all HttpApplication object instances.

Application_Disposed: 
  Fired just before an application is destroyed. This is the ideal location for cleaning up previously used resources.

Application_Error: 
  Fired when an unhandled exception is encountered within the application.

Application_Start: 
  Fired when the first instance of the HttpApplication class is created. It allows you to create objects that are accessible by all HttpApplication instances.

Application_End: 
  Fired when the last instance of an HttpApplication class is destroyed. It's fired only once during an application's lifetime.

Application_BeginRequest: 
  Fired when an application request is received. It's the first event fired for a request, which is often a page request (URL) that a user enters.

Application_EndRequest: 
  The last event fired for an application request.

Application_PreRequestHandlerExecute: 
  Fired before the ASP.NET page framework begins executing an event handler like a page or Web service.

Application_PostRequestHandlerExecute: 
  Fired when the ASP.NET page framework is finished executing an event handler.

Applcation_PreSendRequestHeaders: 
  Fired before the ASP.NET page framework sends HTTP headers to a requesting client (browser).

Application_PreSendContent: 
  Fired before the ASP.NET page framework sends content to a requesting client (browser).

Application_AcquireRequestState: 
  Fired when the ASP.NET page framework gets the current state (Session state) related to the current request.

Application_ReleaseRequestState: 
  Fired when the ASP.NET page framework completes execution of all event handlers. This results in all state modules to save their current state data.

Application_ResolveRequestCache: 
  Fired when the ASP.NET page framework completes an authorization request. It allows caching modules to serve the request from the cache, thus bypassing handler execution.

Application_UpdateRequestCache: 
  Fired when the ASP.NET page framework completes handler execution to allow caching modules to store responses to be used to handle subsequent requests.

Application_AuthenticateRequest: 
  Fired when the security module has established the current user's identity as valid. At this point, the user's credentials have been validated.

Application_AuthorizeRequest: 
  Fired when the security module has verified that a user can access resources.

Session_Start: 
  Fired when a new user visits the application Web site.

Session_End: 
  Fired when a user's session times out, ends, or they leave the application Web site.


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20190211


ref:
http://paladinprogram.blogspot.com/2011/05/globalasax-application.html

Gloabl.asax 的 Application 的事件觸發順序:
  Application_BeginRequest
    Application_AuthenticateRequest
    Application_AuthorizeRequest
    Application_ResolveRequestCache
    Application_AcquireRequestState
    Application_PreRequestHandllerExecute
      HTTP Handler
    Application_PostRequestHandlerExecute
    Application_ReleaseRequestState
    Application_UpdateRequestCache
  Application_EndRequest


在 Global.asax 所定義的事件，依據 ASP.NET Application Events in Global.asax 分類，可以分為：每次頁面的請求都會觸發，與依據條件來觸發兩種。在上圖所表示的，則是每個被使用者要求的頁面都會觸發的事件順序。

舉例來說，如果在 Application_BeginRequest 事件寫一行 Response.Write("paladin"); 則這個網站的每個頁面開頭第一行都會秀出 paladin 這個字眼。

另外依據條件來觸發的事件，則是如下：
Application_Start
  Session_Start
    Application_Error
  Session_End
Application_End
Application_Disposed

從 Visual Studio 2005 開始，預設已經在方案總管理看不到 Global.asax 這檔案了。但如果個人有這方面的需求，還是可以透過新增的方式把這檔案加入。當你打開這 Global.asax 檔案時，會發現他是屬於 Code Inline 的寫法，對於習慣 Code Behind 的人來說，會有一點點不同，詳細的比較可以參考保哥文章(關於 Code Behind 與 Code Inline 開發模式的使用時機與技巧)。假如你想在  Global.asax 撰寫 Application_BeginRequest 事件，則只要直接加入下面一段就可以：

void Application_BeginRequest(object sender, EventArgs e)
    {
        //撰寫自己的 BeginRequest 程式碼
        Response.Write("***************");
    }

Steven Cheng 曾在論壇中提過另外有關 Code Behind 的寫法。
1.在與 Global.asax 同一層的檔案結構，新增一個 globalcode.cs 檔案。並讓這個類別繼承 HttpApplication。

//globalcode.cs
public partial class globalcode : HttpApplication
{
  public globalcode()
  {
  }
  void Application_BeginRequest(object sender, EventArgs e)
  {
    HttpContext.Current.Response.Write("paladin is here..");
  }
}

2.將原先 Global.asax 裡的 
<%@ Application Language="C#"  %>
修改成
<%@ Application Language="C#"  CodeFile="globalcode.cs" Inherits="globalcode" %>

如此，也可以讓 Global.asax 以 Code Behind 來撰寫了。

參考：
01：ASP.NET Application Events in Global.asax
02：如何：使用 Visual C# .NET 建立 ASP.NET HTTP 模組
03：Working with the ASP.NET Global.asax file
04：Application_BeginRequest does not seem to run
05：關於 Code Behind 與 Code Inline 開發模式的使用時機與技巧