Page Life Cycle

Understanding the Page Life Cycle can be very important as you begin to build Pages with MasterPages and UserControls.

Does the Init event fire first for the Page, the MasterPage or the UserControl? 
What about the Load event?

If you make an incorrect assumption about the sequence that these events fire, then you may end up with a page that simply doesn't behave the way you had anticipated.

By running a simple test, we can see exactly when each event fires.  Our test setup is composed of a Page, MasterPage, UserControl, Nested UserControl and Button control as follows:

• <div mce_keep="true">The Page is tied to the MasterPage</div>
• <div mce_keep="true">The UserControl is on the Page</div>
• <div mce_keep="true">The Nested UserControl is on the UserControl</div>
• <div mce_keep="true">The Button is on the Nested UserControl.</div>
• <div mce_keep="true">Clicking the Button calls the Page.DataBind method</div>

Each event on these controls has been set to call Debug.WriteLine as each event is raised.  In addition to the events that get raised for regular pages, I've also set up an HttpModule and wired up all of those events as well. The results in the Debug output window of running this page and Clicking the Button are as follows:

BeginRequest - HttpModule
AuthenticateRequest - HttpModule
PostAuthenticateRequest - HttpModule
PostAuthorizeRequest - HttpModule
ResolveRequestCache - HttpModule
PostResolveRequestCache - HttpModule
PostMapRequestHandler - HttpModule
AcquireRequestState - HttpModule
PostAcquireRequestState - HttpModule
PreRequestHandlerExecute - HttpModule

PreInit - Page

Init - ChildUserControl
Init - UserControl
Init - MasterPage
Init - Page

InitComplete - Page

LoadPageStateFromPersistenceMedium - Page 

ProcessPostData (first try) - Page

PreLoad - Page

Load - Page
Load - MasterPage
Load - UserControl
Load - ChildUserControl

ProcessPostData (second try) - Page

RaiseChangedEvents - Page
RaisePostBackEvent - Page

Click - Button - ChildUserControl

    DataBinding - Page
    DataBinding - MasterPage
    DataBinding - UserControl
    DataBinding - ChildUserControl

LoadComplete - Page

PreRender - Page
PreRender - MasterPage
PreRender - UserControl
PreRender - ChildUserControl

PreRenderComplete - Page

SaveViewState - Page
SavePageStateToPersistenceMedium - Page
SaveStateComplete - Page

Unload - ChildUserControl
Unload - UserControl
Unload - MasterPage
Unload - Page

PostRequestHandlerExecute - HttpModule
ReleaseRequestState - HttpModule
PostReleaseRequestState - HttpModule
UpdateRequestCache - HttpModule
PostUpdateRequestCache - HttpModule
EndRequest - HttpModule
PreSendRequestHeaders - HttpModule
PreSendRequestContent - HttpModule