对于Asp.net页面层开发无论是写页面还是写控件，我觉得都可以用一句话描述:"Do the right thing at the right time in the right place."这是07年底的一篇东西，还是有点价值整理出来与大家共享。 

    本文从两个粒度对Asp.net生命周期做了展示，一是通过记录页面事件的触发顺序看请求的处理流程，一是通过Reflector看Page类内部对请求处理的实现，为了清晰我清理掉了ETW相关的代码保留了一个简化却足可以说明问题的流程骨架；

    本文覆盖以下内容：

1. 页面事件的触发顺序展示
2. 清理掉ETW代码后的，Page类内部对请求处理的实现
3. MSDN关于Asp.net生命周期非常重要的四个表格
4. 演示源代码下载

运行结果：
 

Page_PreInit

Page_Init

Page_InitComplete

Page_PreLoad

Page_Load

Page_LoadComplete

Page_PreRender

Page_SaveStateComplete

点击页面的Button后的输出：

Page_PreInit

Page_Init

Page_InitComplete

Page_PreLoad

Page_Load

Button事件触发！

Page_LoadComplete

Page_PreRender

Page_SaveStateComplete

我们从一个更细的粒度，在Reflector中看Page对请求处理的代码：

MSDN上对Asp.net生命周期解释有非常重要的四个表格：

 

Stage	Description
Page request	The page request occurs before the page life cycle begins. When the page is requested by a user, ASP.NET determines whether the page needs to be parsed and compiled (therefore beginning the life of a page), or whether a cached version of the page can be sent in response without running the page.
Start	In the start step, page properties such as Request and Response are set. At this stage, the page also determines whether the request is a postback or a new request and sets the IsPostBack property. Additionally, during the start step, the page's UICulture property is set.
Page initialization	During page initialization, controls on the page are available and each control's UniqueID property is set. Any themes are also applied to the page. If the current request is a postback, the postback data has not yet been loaded and control property values have not been restored to the values from view state.
Load	During load, if the current request is a postback, control properties are loaded with information recovered from view state and control state.
Validation	During validation, the Validate method of all validator controls is called, which sets the IsValid property of individual validator controls and of the page.
Postback event handling	If the request is a postback, any event handlers are called.
Rendering	Before rendering, view state is saved for the page and all controls. During the rendering phase, the page calls the Render method for each control, providing a text writer that writes its output to the OutputStream of the page's Response property.
Unload	Unload is called after the page has been fully rendered, sent to the client, and is ready to be discarded. At this point, page properties such as Response and Request are unloaded and any cleanup is performed.

 

Life-cycle Events

Page Event	Typical Use
PreInit	Use this event for the following: Check the IsPostBack property to determine whether this is the first time the page is being processed. Create or re-create dynamic controls. Set a master page dynamically. Set the Theme property dynamically. Read or set profile property values. Note: If the request is a postback, the values of the controls have not yet been restored from view state. If you set a control property at this stage, its value might be overwritten in the next event.
Init	Raised after all controls have been initialized and any skin settings have been applied. Use this event to read or initialize control properties.
InitComplete	Raised by the Page object. Use this event for processing tasks that require all initialization be complete.
PreLoad	Use this event if you need to perform processing on your page or control before the Load event. After the Page raises this event, it loads view state for itself and all controls, and then processes any postback data included with the Request instance.
Load	The Page calls the OnLoad event method on the Page, then recursively does the same for each child control, which does the same for each of its child controls until the page and all controls are loaded. Use the OnLoad event method to set properties in controls and establish database connections.
Control events	Use these events to handle specific control events, such as a Button control's Click event or a TextBox control's TextChanged event. Note: In a postback request, if the page contains validator controls, check the IsValid property of the Page and of individual validation controls before performing any processing.
LoadComplete	Use this event for tasks that require that all other controls on the page be loaded.
PreRender	Before this event occurs: The Page object calls EnsureChildControls for each control and for the page. Each data bound control whose DataSourceID property is set calls its DataBind method. For more information, see Data Binding Events for Data-Bound Controls later in this topic. The PreRender event occurs for each control on the page. Use the event to make final changes to the contents of the page or its controls.
SaveStateComplete	Before this event occurs, ViewState has been saved for the page and for all controls. Any changes to the page or controls at this point will be ignored. Use this event perform tasks that require view state to be saved, but that do not make any changes to controls.
Render	This is not an event; instead, at this stage of processing, the Page object calls this method on each control. All ASP.NET Web server controls have a Render method that writes out the control's markup that is sent to the browser. If you create a custom control, you typically override this method to output the control's markup. However, if your custom control incorporates only standard ASP.NET Web server controls and no custom markup, you do not need to override the Render method. For more information, see Developing Custom ASP.NET Server Controls. A user control (an .ascx file) automatically incorporates rendering, so you do not need to explicitly render the control in code.
Unload	This event occurs for each control and then for the page. In controls, use this event to do final cleanup for specific controls, such as closing control-specific database connections. For the page itself, use this event to do final cleanup work, such as closing open files and database connections, or finishing up logging or other request-specific tasks. Note: During the unload stage, the page and its controls have been rendered, so you cannot make further changes to the response stream. If you attempt to call a method such as the Response.Write method, the page will throw an exception.

 

Data Binding Events for Data-Bound Controls

To help you understand the relationship between the page life cycle and data binding events, the following table lists data-related events in data-bound controls such as the GridView, DetailsView, and FormView controls.

Control Event	Typical Use
DataBinding	This event is raised by data-bound controls before the PreRender event of the containing control (or of the Page object) and marks the beginning of binding the control to the data. Use this event to manually open database connections, if required. (The data source controls often make this unnecessary.)
RowCreated (GridView only) or ItemCreated (DataList, DetailsView, SiteMapPath, DataGrid, FormView, Repeater, and ListView controls)	Use this event to manipulate content that is not dependent on data binding. For example, at run time, you might programmatically add formatting to a header or footer row in a GridView control.
RowDataBound (GridView only) or ItemDataBound (DataList, SiteMapPath, DataGrid, Repeater, and ListView controls)	When this event occurs, data is available in the row or item, so you can format data or set the FilterExpression property on child data source controls for displaying related data within the row or item.
DataBound	This event marks the end of data-binding operations in a data-bound control. In a GridView control, data binding is complete for all rows and any child controls. Use this event to format data bound content or to initiate data binding in other controls that depend on values from the current control's content. (For details, see "Catch-up Events for Added Controls" earlier in this topic.)

 

Login Control Events

The Login control can use settings in the Web.config file to manage membership authentication automatically. However, if your application requires you to customize how the control works, or if you want to understand how Login control events relate to the page life cycle, you can use the events listed in the following table.

Control Event	Typical Use
LoggingIn	This event is raised during a postback, after the page's LoadComplete event has occurred. It marks the beginning of the login process. Use this event for tasks that must occur prior to beginning the authentication process.
Authenticate	This event is raised after the LoggingIn event. Use this event to override or enhance the default authentication behavior of a Login control.
LoggedIn	This event is raised after the user name and password have been authenticated. Use this event to redirect to another page or to dynamically set the text in the control. This event does not occur if there is an error or if authentication fails.
LoginError	This event is raised if authentication was not successful. Use this event to set text in the control that explains the problem or to direct the user to a different page.

演示代码下载地址：https://files.cnblogs.com/me-sa/HttpStudy.rar

【本文来自于博客园 作者：坚强2002】