I have two radio button on my asp.net page, with AutoPostBack = True
When I click on either of those, they each set a flag SaveData=False
However, when I click on them, the page_load event occurs first, so the page_load event saves the data, then the radiobutton_OnCheckedChanged event is triggered.
How can I trigger the OnCheckedChanged before the page_load event?
You can't.
You need to read up on the page lifecycle.
You can't trigger the OnCheckedChanged before radiobutton_OnCheckedChanged because that's the normal page life cycle.
You can check in Page_Load if Page.IsPostBack is true or not, and then don't save (or save) the data.
Troy - you will have to take care of this on the client side (javascript / jquery).
Your AutoPostBack = True causes the form to do a postback which calls page load.
Its all about how the page lifecycle and server side events work.
You can't the page always needs to load before events can be fired. This has to do with control creation, view state management, control state, etc.
What you want to do in your Page_Load is something like:
if(!this.IsPostBack)
{
// Do the stuff you want on the initial page load
}
Anything that you do not want to happen when the radio buttons are clicked, put it inside the if {} block. IsPostBack indicates that the page is processing a post-back event, which is what happens when you click one of your radio buttons.
You can't change the order/sequence of event handler execution. However you may move the code inside the page_load to another event handler.
Related
I have a page that creates a list, a button and a textfield dynamically in the Page_Load handler. When you click the button, the text from the textbox is added to the list and everything is re-created by clearing the controls collection of the page and then re-adding all required controls.
So basically, the button gets created two times for every Postback (first in the Page_Load, then in the Button_Click handler).
This only works on the first PostBack. If you try it a second time, the Button_Click handler never gets called (although the dynamic controls get re-created on PostBack).
What am I missing here? Is it possible that the Button_Click event is still wired-up to the first button (the one that was thrown away via Controls.Clear() )?
Page_Load is too late to create the button; it should be in Page init or preinit. If you readd the button, after clearing it, you have to readd the event handler too.
I have finally figured out what the cause of the problem is: when the controls are created more than once, the Event-Handlers (e.g. Button.Click) are also registered more than once. I don't know why, but this causes all of them to stop working. In other words, the events of the disposed Buttons somehow interfer with the events of the actual Buttons.
I solved this by ensuring that the handlers are only registered once (in the Page_Load).
I have a dropdownlist, in the client side, i have it's on change event. If validation is passed, it's selected inded changed event should be fired(server side). My side, the server event is not getting fired. Autopostback is also set is true.
Any suggestion ?
If you are adding the code from the code-behind (as opposed to in the ASPX or ASCX markup), make sure you add it in the Page_Init event or override CreateChildControls. If you want until the Page_Load event to add it, the ASP.NET has already initialized the control state and view state and then will not be aware that the dropdown exists, so when the postback comes it won't know what control to route it to.
Also, in this case, make sure you are always adding the control to the page, not just when Page.IsPostback==false
Make sure your page code is in autoeventwireup = true.
you can check it in your page design page on top.
if autoeventwireup is set to false your event doesn't fire. auto event will set automatically event so it is necessary to write else you have to set event on initialize state.
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.
In my web application I load user controls in the page_loadComplete event. This works fine, however when a button is clicked in a user control, the click event is never fired. Does this has something to do with the page lifecycle? That button click (UI) events occur before the LoadComplete event?
You need to make sure the click event of the button is once again subscribed to, before event handlers fire. LoadComplete happens after control events. For a reference, the ASP.NET Page Life Cycle Overview gives a pretty nice summary.
Snippet:
...
Load
Control events
LoadComplete
PreRender
...
You also need to make sure that the controls that you dynamically load all end up in the same place, so viewstate and controlstate can be reapplied to the same hierarchy as before postback.
Basically, you need to load all dynamic controls on each postback.
Here's someone with the same problem, and solutions to some of them: ASP.NET dynamic controls
Actually what is happening to your situation is, when you click on the button, before event raising, LoadCoplete event fire first in the page lifecycle and same control is again created and here is your event is lost.
Event Handling in ASP.NET page happens after Validation and before Rendering phase. And Validation phase happens after Load.
LoadComplete happens after Control events and before RreRender event.
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