I'm looking for a good tutorial/article that explains the exact sequence of events that takes place when a page is created. I can never remember the order. I think it's something like the parent controls Init event is called, then the child controls Init event is called, in order of the placement on the page. Also, when the control events are called, what order are they called in? For example, if a button event is raised, does this event get called before a DataList_ItemDataBound event is called if the DataList.DataBind is in the Page_Load event? So, does anyone want to try to explain or direct me to a nice article that explains all this?
thanks.
This link should cover it:
MSDN Page Life Cycle
Maybe you're looking for this:
by Leon Andrianarivony.
This is a good article I refer to for these types of questions.
http://www.aspfree.com/c/a/ASP.NET/ASP.NET-Life-Cycle-and-Best-Practices/
And to answer your question specifically - Button events run after everything in Page Load is completed so if you're calling a DataBind in Page_Load, the button click event comes after that.
Related
This is a little difficult to explain so please bear with me.
I have a procedure that is generating some radio buttons and assigning a CheckedChanged postback event based on the level being passed through (up to 4 levels). When the first level is checked (radio button selected) the postback event rb_CheckChanged00() is called and a check is done to see if this item has any children, if it does, it will create more radio buttons and assign rb_CheckChanged01 to the CheckChanged event for these - This part is working fine.
The issue I have is when I select the second Radio Button that has been created (the child), it doesn't seem to go to the post back event at all. The page is posting back when I click on it but everything resets because it won't go into rb_CheckChanged01.
I know this info is quite vague but I am hoping someone has an idea on how the post back event works and if I am somehow using it incorrectly.
Using: ASP.NET 2.0, IIS7
Thanks.
Most of the time when the dynamically created control's events are not fired, it's because the controls are 'reset' upon postback.
To make sure the same controls get created each and every time make sure that the control's IDs are set to the same values each and every time, before the ViewState is loaded. This way, when the control is added to the control collection of the page, once the ViewState is loaded, it'll persist it's properties. (just to describe what happens, in a nutshell)
One of the best articles I've read on this topic is this one. Make sure you read it, to fully understand what's happening in the background.
Looks like the child RBs are cleaned before they are able to trigger the event. From my personal experience, it's best to keep track of those dynamically generated objects, and regenerate them in every postback. The events will start to trigger :)
Your controls and events are not registered in the ViewState because dynamic controls need to be loaded in the Page_Init. Because they're not persisted in the ViewState, they won't be registered with events. A similar question:
Problem with dynamic controls in .NET
Only 1 thing can cause this, you create the rb's on page_load and don't add them to a List<> or something similar and that object to Session. What you need to do is when you create the items, Add them to a List and add that list to Session["RadioButtons"] and if the Page.IsPostBack is true, load your controls one by one from your list which is kept in your session to your page.
I have a control which has an ImageButton which is tied to an OnClick event... Upon clicking this control, a postback is performed and the event handler is not called. AutoEventWireup is set to true, and I've double checked spelling etc.... We haven't touched this control in over a year and it has been working fine until a couple of weeks ago.
We have made changes to controls which load this control... so I'm wondering, what kind of changes could we have made to stop this event handler from being called? There is quite a bit of Javascript going on, so this could be the culprit too...
Edit: Some clarification... we are dynamically loading the parent control of the ImageButton in the OnLoad event of the page... if that makes sense.
AutoEventWireup is irrelevant. Is your ImageButton loaded dynamically, i.e. not written out in mark up? If it is loaded onto the page late in the Page lifecycle e.g. in PreRender then the event will not fire.
If there is a JavaScript issue your page will not even PostBack. Is that happening?
Did you give the ImageButton an ID?
I def agree with what BritishDeveloper said. I had a similar problem where I was dynamically loading controls, but I couldn't get a reference to the control using Page.FindControl("controlName") Someone pointed out that I needed to keep the page lifecycle in mind. I found out I needed to make sure to load the control in the PageInit because after doing an async postback the control was still there, but not loaded in the postback so there was no way to find it. This was all in csharp codebehind and ajax though, but I'm guessing the control isn't getting reloaded.
So, as it turns out we set the PostbackUrl property on one of our buttons in control A... this caused the event handlers for control B not to fire when a button in control B was pressed.
If you create a control dynamically. Any time you fire a postback using the new created control, you need to recreated it. Just think that your application are running at a server. How can the server hold information on controls created dynamically? Don't use Page.IsPostBack to create postback. PostbackUrl is bad solution. Workarround will be need.
I can go into a little more detail ... I just lost several hours fixing my own issue similar to the issue described here. In the course of creating some search controls, I added a pair of ImageButtons and set the PostbackUrl properties on them. A few days later while testing new code, I noticed that none of my other buttons on the webform were posting back properly. They would fire a postback, but the code-behind was behaving as if every postback was an initial page request and none of the event handlers were firing.
After several hours of troubleshooting, I came across this post. When I went back and removed the PostbackUrl from those two ImageButtons, everything went back to normal. I don't know why it was causing this issue, but the fix mentioned here worked for me. I want to add that my ImageButtons were not dynamically added ... they were in the markup and this issue still cropped up. Search your markup for any controls with PostbackUrl set ... remove that (program around it if needed) ... see if your event handlers will fire properly.
Is there any kind of event out there that would allow for a preload post back event.
The reason I ask is I have a control that adds sibling controls to it on postback events, however, by the time it has loaded the post back its too late to add the new control to the control collection. Therefore, the controls are never updated correctly.
Thanks!
Try the Init event.
Override CreateChildControls (make sure to call base!). In your postback event handler, make sure you are storing somewhere the list of controls that should be created dynamically, so when CreateChildControls gets invoked very early in the lifecycle on the next go-round, it will recreate the controls built on the last postback.
Here is a quick hack. You can always, query the __EventTarget and or the value of the submit button in init and can load dynamically the control.
But doing so, may not be appropriate as your control hierarchy would change and could cause problems.
As above, dynamic controls have to be added during the page Init event, so that they can be properly handled within the page's Viewstate. You might want to turn the Viewstate off for the page as well, since it can fire errors at you if the controls change.
As has already been stated the proper place to add dynamic controls is in the Init event.
Here's an article with more information.
Dynamic Web Controls, Postbacks, and View State
To get a better understanding of the ASP .NET page life cycle see:
ASP.NET Page Life Cycle Overview
This page explains the event order (and what happens in each one) in a postback, it helped me more than once.
I've just found this link, that can also be of use to you
Is it possible to get a list of control events that are going to fire before they happen, say inside the Page_Load handler?
For example if a button was clicked can I figure this out before the button_click event handler is called?
You've picked a really tough question... the reason for this is that there are several ways that events will fire.
1) __EVENTTARGET (as mentioned above)
2) If the name of your button is MyButt, then you'll see "MyButt=" in the query string.
3) When each control (like, a TextBox for example) checks the request to see if it's value in the ViewState is different than posted, then a "Text_Changed" will fire.
But, you can use #1, and #2 to check a few places.
Unfortunately, interrogating the __EVENTTARGET value won't do the trick. Often, that value will be empty. The postback processing makes some decisions about what events to raise based on more than just the event target value (if any) testing control state values against the values posted by the form (such as for a textbox) determines whether events like TextChanged should be raised.
Aside from actually hooking up an event handler to all the controls you wish to capture events for, I don't think there is any way to determine it. It might be possible to do basically what the framework does though. You would need to do it between when the controls have been created and viewstate has been restored but before the posted values are processed. You could compare the current control values (from viewstate) with the posted values, essentially determining what events would fire.
What is your goal with this? Perhaps there is a better solution.
The following contains the mangled id for a button when clicked.
Page.Request.Form["__EVENTTARGET"]
Here is an example that I believe answers your question.
Another way would be just to set some breakpoints when debugging.
I have an asp.net web page with a ton of code that is handled in the Page-Load event of the page. I also have a dropdown box on the page that should reload the page with a new value, but I would like to get this new value before I process the entire Page-Load code.
I am trying to get my head around ASP.NET page lifecycle.
Should I move the Page-Load code to a later event or is there a way to get the value of the dropdown list value before the the Page-Load event begins?
TIA
I would use Page_PreLoad instead of Page_Init, because it is raised after all postback data is processed.
Try Page_Init
As noted before, Page_Init is what you want. But I emplore you to make your pages as loosly coupled as posible. Look into the MVP pattern for starters. Also, make sure that most of your logic is in your domain objects.
There shouldn't be too much code in the Page_Load event. If there is, it shoud be broken up into concise methods so that you don't have crazy code.