In this article, we are going to discuss the different methods and order they are executed during the load of an .aspx web page.
Methods
|
Description
|
Page_PreInit
|
Before page Initialization
|
Page_Init
|
Page Initialization
|
LoadViewState
|
View State Loading
|
LoadPostData
|
Postback Data Processing
|
Page_Load
|
Page Loading
|
RaisePostDataChangedEvent
|
PostBack Change Notification
|
RaisePostBackEvent
|
PostBack Event Handling
|
Page_PreRender
|
Page Pre Rendering Phase
|
SaveViewState
|
View State Saving
|
Page_Render
|
Page Rendering
|
Page_Unload
|
Page Unloading
|
PreInit : The entry point of the
page life cycle is the pre-initialization phase called “PreInit”. You
can dynamically set the values of master pages and themes in this event.
You can also dynamically create controls in this event.
Init : This event fires after
each control has been initialized, each control's UniqueID is set and
any skin settings have been applied. You can use this event to change
initialization values for controls. The “Init” event is fired first for
the most bottom control in the hierarchy, and then fired up the
hierarchy until it is fired for the page itself.
InitComplete: Raised once all
initializations of the page and its controls have been completed. Till
now the viewstate values are not yet loaded, hence you can use this
event to make changes to view state that you want to make sure are
persisted after the next postback
PreLoad : Raised after the page
loads view state for itself and all controls, and after it processes
postback data that is included with the Request instance
(1)Loads ViewState : ViewState data are loaded to controls
(2)Loads Postback data : postback data are now handed to the page
Load: The
important thing to note about this event is the fact that by now, the
page has been restored to its previous state in case of postbacks. Code
inside the page load event typically checks for PostBack and then sets
control properties appropriately. This method is typically used for most
code, since this is the first place in the page lifecycle that all
values are restored. Most code checks the value of IsPostBack to avoid
unnecessarily resetting state. You may also wish to call Validate and
check the value of IsValid in this method. You can also create dynamic
controls in this method.
Control (PostBack) event(s) :ASP.NET
now calls any events on the page or its controls that caused the
PostBack to occur. This might be a button’s click event or a dropdown's
selectedindexchange event.
LoadComplete :This event signals the end of Load.
PreRender : Allows final changes
to the page or its control. This event takes place after all regular
PostBack events have taken place. This event takes place before saving
ViewState, so any changes made here are saved. For example : After this
event, you cannot change any property of a button or change any
viewstate value. Because, after this event, SaveStateComplete and Render
events are called.
SaveStateComplete :Prior to this
event the view state for the page and its controls is set. Any changes
to the page’s controls at this point or beyond are ignored.
Render : This is a method of the
page object and its controls (and not an event). At this point, ASP.NET
calls this method on each of the page’s controls to get its output. The
Render method generates the client-side HTML, Dynamic Hypertext Markup
Language (DHTML), and script that are necessary to properly display a
control at the browser.
UnLoad : This event is used for
cleanup code. After the page's HTML is rendered, the objects are
disposed of. During this event, you should destroy any objects or
references you have created in building the page. At this point, all
processing has occurred and it is safe to dispose of any remaining
objects, including the Page object. Cleanup can be performed on-
(a)Instances of classes i.e. objects
(b)Closing opened files
(c)Closing database connections
Below is example of the ASP.Net Life Cycle
HTML Default.aspx
<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
<title>Untitled Page</title>
</head>
<body>
<form id="form1" runat="server">
<div><asp:Button ID="Button1" runat="server" OnClick="Button1_Click" Text="Page Button" /></div>
</form>
</body>
</html>
Code Default.aspx
using System;
public partial class _Default : System.Web.UI.Page
{
int i = 0;protected void Page_PreInit(object sender, EventArgs e){Response.Write( "" + (++i).ToString() + " Page Pre-Init");
}protected override void OnInit(EventArgs e){Response.Write("" + (++i).ToString() + " Page Init");
}protected void Page_InitComplete(object sender, EventArgs e){Response.Write("" + (++i).ToString() + " Page Init Completed");
}protected void Page_Load(object sender, EventArgs e){ViewState["test"] = "Test";Response.Write("" + (++i).ToString() + " Page Load");
}protected override void OnPreRender(EventArgs e){Response.Write("" + (++i).ToString() + " Page Pre Render");
}//protected override void Render(HtmlTextWriter writer)//{// //Response.Write("" + (++i).ToString() + " Render");
//}protected void Button1_Click(object sender, EventArgs e){Response.Write("" + (++i).ToString() + " Page Button Click");
}protected override void OnUnload(EventArgs e){// Response.Write("" + (++i).ToString() + " Unload");
}public override void Dispose(){// Response.Write("" + (++i).ToString() + " Dispose");
}protected override object SaveViewState(){Response.Write("" + (++i).ToString() + " Page Save View State");return base.SaveViewState();}public void RaisePostBackEvent(string eventArgument){Response.Write("" + (++i).ToString() + " Page Raise Post Back Event");
}public void RaisePostDataChangedEvent(){Response.Write("" + (++i).ToString() + " Page Raise Post Data Change Event");
}protected override void LoadViewState(object o){Response.Write("" + (++i).ToString() + " Page Load View State");base.LoadViewState(o);
}private void Page_LoadComplete(object sender, System.EventArgs e){Response.Write("" + (++i).ToString() + " Page Load Completed");}
}
OUTPUT
When a page request is sent to the Web
server, the page is run through a series of events during its creation
and disposal as below only Page_Unload and Dispose are not shown here.
Suppose the Button event get fire then it will create event as below (again Page_Unload and Dispose are not shown here because page already load when these event occurs)
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