I am having an issue with an image button being clicked, and then the on click event of that button is not being fired, part of the issue I think is that a validator on the page is firing and then suppressing the button click, but I cannot find what is causing it.
Is there any way to see the events that a request goes through?
I assume that there is something is happening before the post back occurs, as I can catch the page as it comes back to Page_Load, but I need to know what is happening before that.
Is this even possible to find out?
is it an ImageButton ? If yes, set CauseValidation to false.
You can get some info by enabling tracing for the page.
Before Load, you only have PreInit at the Page level, followed by Init for all Controls (bottom-up), Init for the Page, then InitComplete for the Page, then Load for the Page, then Load for all Controls (top-down).
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I'm a newbie to ASP.Net, so my question might be a little bit dumb, I don't quite understand how each stage works in ASP.Net page life cycle, I wrote some code includes a simple page with a label control and a button control on it and found the sequence is :
1.Page initialization event handled.
2.Page load event handled.
3.Page prerender event handled.
4.Page load event handled.
5.Page postback event handled.
6.Button click event handled.
7.Page prerender event handled.
My questions are:
Why some events like page load are raised twice?
People usually said page_load event happens before button click event. I don't quite get it, do people mean page_load event is handled before button click event? if yes then I understand, so is it just something like when we click a submit button, we actually fire 2 events, one for button click event, and one for page load event and page load event is handled first?
Can anyone put these stages in a simple way to explain how each stage steps in? like when a user clicks a button, what's happening behind the scene
Why some events like page load are raised twice?
The PageLoad event is raised once per page request from the server. When an asp.net page is posted back to the server, it's PageLoad event will be called again. If you check your IIS logs, you should see two requests for the page from your browser/client. The first will be the original request for the page, and the second one will be after your button press (which I assume is causing the post back).
People usually said page_load event happens before button click event. I don't quite get it, do people mean page_load event is handled before button click event? if yes then I understand, so is it just something like when we click a submit button, we actually fire 2 events, one for button click event, and one for page load event and page load event is handled first?
In the lifetime of you an asp.net page, it begins when a client requests the page, and ends after the page is rendered to the client. The link sent to you by Andrew Shepherd provides a very good tutorial on the asp.net page life cycle. Be sure you read this and understand it.
Can anyone put these stages in a simple way to explain how each stage steps in? like when a user clicks a button, what's happening behind the scene?
It really depends on what you've got wired up to the button. The button could cause client-side scripting to execute, or it could cause some action to take place on the web server.
Not sure if this is the prescribed order of events, but I have a logout button on my masterpage, whose event doesn't fire until after the content page's page_load fires.
On some pages there is some time-consuming code in page_load, and this makes the logout process take way too long.
The catch-22 is that in the content's Page_Load, I can't check any property I might set in the Master's logout_click event, because it hasn't fired yet.
How can I make the MasterPage's logout button fire first and go directly to the redirect which I have in the click event?
Thanks very much,
JimO.
What you are facing is the default behavior due to page life cycle.
But you can try the following steps to work around your problem
Instead of having a Button/LinkButton and writing code for LogOut on master page in Click event, you can have a HyperLink.
Set its NavigationURL to point to a logout page which will handle only the code for LogOut.
Write the LogOut code in the Page_Load event of that page.
Most people put something like the following in their page_load
if (!Page.IsPostBack()) {
// do stuff to initialize everything
}
This way when a postback occurs you don't necessarily have to reload a bunch of stuff.
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.
When an asp.net button is fired, will the button's event get fired before the page_load and init and pre_init events?
http://msdn.microsoft.com/en-us/library/ms178472.aspx
Page_Load goes before event handlers.
Just stick some breakpoints in the different functions and see which one fires first. I think the answer is no.
Make a page with page init, load (also variations of ispostback), prerender, unload and control events and do a trace to see when they all fire off - easier to remember too when you do it as opposed to reading it.
Page_Load, init and pre_init will happen before the button can receive any user input, so it will definitely happen before the button can fire off any events as a result of user input.
When loading a page for the first time (!IsPostback), I am creating a button in code and adding it to my page, then adding an event handler to the click event.
However, when clicking the button, after the page reloads, my event handler does not fire.
Can anyone explain why?
#Brad: Your answer isn't complete; he's most likely doing it too late in the page lifecycle, during the Page_Load event.
Okay, here's what you're missing.
ASP.NET is stateless. That means, after your page is rendered and sent to the browser, the page object and everything on it is destroyed. There is no link that remains on the server between that page and what is on the user's browser.
When the user clicks a button, that event is sent back to the server, along with other information, like the hidden viewstate field.
On the server side, ASP.NET determines what page handles the request, and rebuilds the page from scratch. New instances of server controls are created and linked together according to the .aspx page. Once it is reassembled, the postback data is evaluated. The viewstate is used to populate controls, and events are fired.
This all happens in a specific order, called the Page Lifecycle. In order to do more complex things in ASP.NET, such as creating dynamic controls and adding them to the web page at runtime, you MUST understand the page lifecycle.
With your issue, you must create that button every single time that page loads. In addition, you must create that button BEFORE events are fired on the page. Control events fire between Page_Load and Page_LoadComplete.
You want your controls loaded before ViewState information is parsed and added to controls, and before control events fire, so you need to handle the PreInit event and add your button at that point. Again, you must do this EVERY TIME the page is loaded.
One last note; page event handling is a bit odd in ASP.NET because the events are autowired up. Note the Load event handler is called Page_Load...
You need to add the button always not just for non-postbacks.
If you are not reattaching the event handler on every postback, then the event will not exist for the button. You need top make sure the event handler is attached every time the page is refreshed. So, here is the order of events for your page:
Page is created with button and event handler is attached
Button is clicked, causing a postback
On postback, the page_load event skips the attaching of the event handler becaue of your !IsPostback statement
At this point, there is no event handler for the button, so clicking it will not fire your event
That is because the event binding that happens needs to be translated in to HTML. This postback that happens if bound to the page between OnInit and OnLoad. So if you want the button to bind events correclty make sure you do the work in OnInit.
See the Page Life Cycle explaination.
http://msdn.microsoft.com/en-us/library/ms178472.aspx