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 | haidar_bilal | | Asp.Net User |
| Page Life Cycle | 6/11/2005 10:54:15 AM |
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I guess this is the best place for my post, if not please my friends(moderators) move it. I have a question about Page-Life Cycle in asp.net 2.0. First of all: 1- PreInit() is called, where the personalization and themes data are initialized 2- Init() is called, in this stage, Each control on the page will initialize and configure its state. -------------------------- TrackViewState() is called -------------------------- 3- Init() Complete, ensures that all page's controls have been initialized 4- Control State and View State: Control state first, where the state of the controls is being loaded, then View State is loaded. My question here is, I know that some controls might have specific properties that need to be loaded, and ViewState is usually for controls to load their state upon postback right? So, why do we need those two notions? 5- Load PostData: All controls that Implement IPostBackDataHandler, would load their values here. I wonder, in the previous point, we said controls load their state, what if those controls implements IPostBackDataHandler, this means that their state will be loaded in the previous method right? Then, my question would be, State doesn't include the data too? If yes, then even if a control implements IPBDH, its postedback data won't be retrived here, since they were already retrieved before, when the control state was laoded right? If the state doesn't include loading data, then its fine. 6- PagePreLoad: Used only if you handle any event before pageLoading. 7- PageLoading method: It is fired for all child controls, up to the parent control. First of all, the page makes a second call to load postedback data right? Then, handles any callback event, then the control's events if fired, like textbox text changed. 8- PostBack events method: Events that have been defined by the user, for example, on click execute a certain method. 9- PageLoad event ends: 10: PreRender method: Ensures all controls have been created. Start rendering from the page control to the children control. Ensures that the personalization data, control and viewstate are saved. 11- Render method, where the markup is rendered of the page. 12- Page UnLoad. I would like to know if this is the correct page-life cycle. Differentiate between Control State loaded in the ControlState Loaded method and the LoadPostBack() method. One thing also, usually when we say load post data, where would be saved, in viewstate?? It has always been a question for me. ![Smile [:)]](/emoticons/emotion-1.gif) Now, I have a question about Cross-Page, can it be used for remote pages? I mean, can I post to a page that is not part of my web application? Or, it should be a local posted page? Finally, I have a question about callback(). I guess after a call back there will be a page postback, but however, after pageload ends method, the RaiseCallBackEvent will get fired and no rendering, so callback() means only that no new rendering ? another postback, but the page's control won't be rendered again? Regards
Bilal Hadiar, MCP, MCTS, MCPD, MCT Microsoft MVP - Telerik MVP |
| wessamzeidan | | Asp.Net User |
| Re: Page Life Cycle | 6/11/2005 12:06:50 PM |
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I can answer the question regarding the controlstate and viewstate. In ASP.NET 2.0, viewstate has been split into 2 parts, the normal viewstate that we already know from ASP.NET 1.x, and the new controlstate. Control state is basiclly viewstate that you can't disable, its used to save the state that the control cannot not function without. The ASP.NET guys invented it for performance reasons, usually when you want to minimize the size of the viewstate of a page, you disable the viewstate of some controls on the page, but by disabling the viewstate of a control, all the properties of that control loose its state between postbacks, and some of these properties are very critical for a control to function. So in ASP.NET 2.0, the state of these critical properties has been moved to controlstate, which cannot be disabled, but you can still disable the viewstate of the control.
Regarding the IPostBackDataHandler thing, controls that implement this interface load some properties from the data posted by the control. Lets take the textbox for example, lets say that you're requesting a page in which you change the value of the Text property of a text box in page load event, the value of this property will be saved in the viewstate. You change the value of the textbox in the browser and then do a postback. When page lifecycle reaches the loadviewstate stage, the Text property of the textbox gets loaded from the viewstate (which is the value that has been set in the page load event from the previous request). When the page life cycle reaches the load post data stage, the Text property gets loaded again, but this time with the data that you entered in the textbox in the browser. So the Text property gets loaded twice, once from the viewstate and once from the postback data.
Hope this explains some of your points.
Wessam Zeidan |
| WilcoB | | Asp.Net User |
| Re: Page Life Cycle | 6/11/2005 12:26:20 PM |
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4- Control State
and View State: Control state first, where the state of the controls is
being loaded, then View State is loaded. My question here is, I know
that some controls might have specific properties that need to be
loaded, and ViewState is usually for controls to load their state upon
postback right? So, why do we need those two notions?
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Unlike viewstate, controlstate can not be disabled. Control state
(generally/should) contain(s) state that a control relies on for it to
work properly. For example, a datagrid in .NET 1.x which viewstate
disabled doesn't properly page, etc. You were on your own when all you
often wanted is disable all viewstate, except those few things that
made the datagrid function properly (like paging). Control state solves
this.
5- Load PostData:
All controls that Implement IPostBackDataHandler, would load their
values here. I wonder, in the previous point, we said controls load
their state, what if those controls implements IPostBackDataHandler,
this means that their state will be loaded in the previous method
right? Then, my question would be, State doesn't include the data too?
If yes, then even if a control implements IPBDH, its postedback data
won't be retrived here, since they were already retrieved before, when
the control state was laoded right? If the state doesn't include
loading data, then its fine.
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The viewstate includes the previous data. The posted data is the current data (e.g. the new text in a textbox). It relies on the state data to be able to raise events like TextChanged.
7- PageLoading
method: It is fired for all child controls, up to the parent control.
First of all, the page makes a second call to load postedback data
right? Then, handles any callback event, then the control's events if
fired, like textbox text changed.
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After the page was loaded, postback change events are raised, such as TextChanged.
10: PreRender
method: Ensures all controls have been created. Start rendering from
the page control to the children control. Ensures that the
personalization data, control and viewstate are saved.
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Add to that: register client script.
One thing also, usually when we say load post data, where would be saved, in viewstate?? It has always been a question for me.
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It's not really saved - its usually posted by the user (e.g. from a
textbox or some other kind of input field). Once its posted, it can be
stored in the viewstate field (used by both control- and viewstate), so
that after the next postback you still have this data. But in that
case, its loaded in the control after the state is loaded, and not
after postback data was loaded.
Now, I have a
question about Cross-Page, can it be used for remote pages? I mean, can
I post to a page that is not part of my web application? Or, it should
be a local posted page?
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Never tried it, but I'm sure that's not going to work. ASP.NET needs to
be able to access the source files, and be able to do pretty much with
it what it could do with any other (active) page. It needs to be able
to build the control hierarchy, etc., so that you can use FindControl
and stuff. Without the source, thats pretty much impossible.
Finally, I have a
question about callback(). I guess after a call back there will be a
page postback, but however, after pageload ends method, the
RaiseCallBackEvent will get fired and no rendering, so callback() means
only that no new rendering ? another postback, but the page's control
won't be rendered again?
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It's not really a postback. But stuff like viewstate is posted. During
a callback, there's a slightly different and smaller life cycle.
Nothing will be rendered for example. Instead, data is returned which
will be available on the client (e.g. for "rendering" it there).
Your vision on the life cycle isn't 100% accurate (e.g. missing stuff
like InitComplete, but overall I think you've got it pretty much at the
right end.
- Wilco Bauwer / http://www.wilcob.com |
| haidar_bilal | | Asp.Net User |
| Re: Page Life Cycle | 6/11/2005 2:43:48 PM |
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First of all, thank you Wessam and thank you WelcoB.
Regarding the page-life cycle, you mentioned WelcoB that I missed the
InitComplete, well I knew about it in fact, but missed it in the post,
you are right. Other than that, is there any thing still missing. To
me, I beleive understanding the basic of how the request is going,
better first than start with any new feature of the technology.
There is a conflict between what Wessam said and WelcoB.
Wessam said, the TextBox for example, will be loaded twice from the
ViewState and the Postedback data, while WelcoB said that the ViewState
will hold the previous data and the LoadPostData will have the current
data, what do you think ?
I kind mixe between ViewState and LoadPostBackData, why do we have
both? When we say the control state will load critical state of the
control, will it load also the Data? I got to know what might be a good
example of a critical state, from the example given by WelcoB, but why
do we have those two seperate steps? ViewState and LoadPostBackData ?
Does it mean we can now disable ViewState all the times? Since the
controls will have their own ViewState? Do we need the ViewState for
other needs than for controls? I don't think so, do you agree with me?
do we still need ViewSate? Maybe ControlState loads only critical set
right? So we still need the ViewState to load the other non-critical
set, but here comes again, if the control's non-critical state is
loaded by the ViewState, why do we still have LoadPostBackData?
Correct me if I am mistaken, LoadViewState will get back the control's
state from the hidden fields right? then the LoadPostBackData will
assign the data to controls from the ViewState? I am really kind of
mixed here.
then, we have SaveViewState and SavePostBackData, the first will save
the state in hidden fields, the second where will it save them?
Thanks a lot.
WelcoB, it seems you are well knowledgable about ASP.NET 2.0, any good "special" resources you can point us to ?
Regards
Bilal Hadiar, MCP, MCTS, MCPD, MCT
Microsoft MVP - Telerik MVP
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| WilcoB | | Asp.Net User |
| Re: Page Life Cycle | 6/11/2005 3:07:49 PM |
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I kind mixe between ViewState and LoadPostBackData, why do we have
both?
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Imagine the following. Someone enters some text in a textbox. After a
postback is done, this text will be stored in the viewstate. If you
would then postback again, the viewstate holds the data entered in the
textbox. At that point, both LoadViewState and LoadPostBackData result
in loading the same data twice, unless the textbox was made
invisible, in which case only LoadViewState would load the text. The
reason why the text is stored in viewstate is that it can both
differentiate the previous text and the current text, and use that to
determine whether TextChanged should be raised, and it can be used to
'remember' the entered text even when the textbox is made invisible
after a postback.
I got to know what might be a good
example of a critical state.
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The current page in a datagrid.
do we still need ViewSate?
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ViewState can still be used to decrease server load. For example, by
enabling viewstate, you can prevent a query to be required on the
server after a postback to bind a datagrid.
....and SavePostBackData...
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SavePostBackData? There's no such thing. In case of a textbox, after
the postback data was loaded, and a textbox knows that it should raise
the TextChanged event, it can store the current value in the viewstate
(and overwrite its previous value if applicable).
WelcoB, it seems you are well knowledgable about ASP.NET 2.0, any good "special" resources you can point us to ?
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(It's Wilco ;)). Reflector is a great tool to understand what's going
on under the hood. Nikhil Kothari's server controls & components is
a great book. Those are the best 2 resources one needs, imo :). I've
been developing production software since beta 1, which helped a lot to
understand most of the things in ASP.NET 2.0.
- Wilco Bauwer / http://www.wilcob.com |
| haidar_bilal | | Asp.Net User |
| Re: Page Life Cycle | 6/11/2005 3:23:39 PM |
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Hello, I didn't read your reply yet, but I got something while browsing through the reflector,
bool IPostBackDataHandler.LoadPostData(string postDataKey, NameValueCollection postCollection)
{
string text1 = this.Text;
string text2 = postCollection[postDataKey];
if (!text1.Equals(text2))
{
this.Text = text2;
return true;
}
return false;
}
What I conllcude is the following:
LoadPostData is only fired when the text inside the textbox is changed.
this means that the ViewState will always try to load data into the textbox, (old data)
Only, when text changes in the textbox, the LoadPostData will be fired,
Now this makes sense, and it seems that, both Wessam and Wiclo are correct why?
Its true what Wilco said, about "previous" and "current" data.
And Wessam said that the textbox will be loaded twice, well not sure I guess, ViewState will retain
the old value of the Textbox, only once inthe LoadViewState, and if nothing changed in the text,
then the TextBox will be previously loaded and no need to load it again, bt if text changed then
LoadPostData will fill the new data,
Is that right?
Regards
|
Bilal Hadiar, MCP, MCTS, MCPD, MCT Microsoft MVP - Telerik MVP |
| WilcoB | | Asp.Net User |
| Re: Page Life Cycle | 6/11/2005 3:36:24 PM |
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LoadPostData will be called for each control which posted data. In the
case of the TextBox it will be loaded when text was entered in the
textbox. Let me guide you through the LoadPostData implementation you
pasted:
string text1 = this.Text; // The "previous" Text. The Text property gets the text from the viewstate.
string text2 = postCollection[postDataKey]; // The text in the textbox, e.g. the "current" posted text
if (!text1.Equals(text2)) // Check if the text is changed.
{
this.Text = text2; // Update the current text (the
Text property sets the text in the viewstate - so once SaveViewState is
called, the current text will be stored in the viewstate)
return true; // Data was changed, so return true so that the RaisePostDataChangedEvent method will be called.
}
return false; // No data was changed, so return false so that the RaisePostDataChangedEvent method will NOT be called.
- Wilco Bauwer / http://www.wilcob.com |
| wessamzeidan | | Asp.Net User |
| Re: Page Life Cycle | 6/11/2005 3:53:22 PM |
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 haidar_bilal wrote: | And Wessam said that the textbox will be loaded twice, well not sure I guess, ViewState will retain
the old value of the Textbox, only once inthe LoadViewState, and if nothing changed in the text,
then the TextBox will be previously loaded and no need to load it again, bt if text changed then
LoadPostData will fill the new data |
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Well Bilal, when I said that value of the Text property will be loaded twice, I meant for the example I gave you. And as Wilco said, LoadPostData will be called any way for a textbox, the RaisePostDataChangedEvent method call depends on it.
Wessam Zeidan |
| haidar_bilal | | Asp.Net User |
| Re: Page Life Cycle | 6/11/2005 4:10:23 PM |
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Ok, Ok, Ok
I got it now.
LoadPostData will always be called, it is used to track changes in the
text of the TextBox, if textchanges, it will RaisePostBackEvent, else
nothing will be called.
This explains to me why for example HyperLink doesn't implement IPostBackEventHandler, since no need to get anything from postback.
I kind of had problems all the time with ViewState and LoadPostData, I ued them for granted, but now I got the idea.
Thanks a lot Wessam and Wilco.
Regards
Bilal Hadiar, MCP, MCTS, MCPD, MCT Microsoft MVP - Telerik MVP |
| clintonG | | Asp.Net User |
| Re: Page Life Cycle | 9/9/2005 5:14:34 PM |
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I have unresolved issues in this same context that have brought development to a complete stand still. A LinkButton control within a Panel control will load a content page within a MasterPage when the LinkButton click event is raised but the LinkButton event does not PostBack and both the Panel and LinkButton disappear from the ViewState.
How can the content page even load without a PostBack? Why do the controls disappear from theViewState?
Please review this topic [1] and help me understand what can be done.
[1] http://forums.asp.net/1039817/ShowPost.aspx
<%= clintonG |
| clintonG | | Asp.Net User |
| Re: Page Life Cycle | 9/21/2005 1:18:05 AM |
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