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).
Related
I have the following scenario:
UserControlA contains a <asp:Button id="bSomeid" onClick="AddItem" /> with some code to an item to a shopping basket in AddItem.
UserControlB contains some LinkButton's that dynamically add a selection of UserControlA to the page in the OnClick event.
This is all done in an UpdatePanel. It is a little more complicated but I have pruned the information to what I believe is causing the problem, I will add more information if necessary.
The problem I have is that it takes 2 clicks for the AddItem event to trigger after I have added the items to the page after clicking the LinkButton.
I understand why this is happening - it is to late in the page cycle to register events for the next post back in the onclick - but can anyone think of a way around this? Can I force an event to be triggered on the next postback? I have tried to think of a way to run my code in page_load but I requuire access to the sender in the onClick.
Using .NET 4.0.
EDIT
I managed to find a way to get the link button sending the request in the Page_Load (using Request.Form["__EVENTTARGET"];) so I moved my code to the Page_load event. It still requires 2 clicks so I am assuming it isn't something to do with the onClick being registered to late.
Are there any other general things to check that could cause a button to require 2 clicks to post an event properly?
If your suspicion about being late in page life cycle is true then you can try using ScriptManager.RegisterAsyncPostBackControl method to register dynamically added controls in the link button click - considering that your button is within user control, you need to add public method into UserControlA that would actually register the button bSomeid1 and link button click from UserControlB would actually call the A control's method.
EDIT :
Another cause for button click not happening can be that button being dynamic control is not added in the page hierarchy when post-back happens (or it gets added very late in the page life cycle when the post back data is already processed). A really full-proof solution should add dynamic controls back to the page hierarchy in page_load it-self (and strictly maintaining same controls ids within hierarchy). If that's not possible then you can sniff the request (Request.Form) to detect the post-back.
In your case, you should ascertain if the button is indeed causing the post-back on each click. If yes, what is the POST data (Request.Form) for the first request - what is the __EVENTTARGET value on the first click (and post-back)? That should start your trouble-shooting.
On the other hand, a simple work-around could be to use html anchor element (you can still use link button) and have a javascript handler in the click event that would set some hidden variable and then submit the form (you can simulate the click on hidden button to trigger ASP.NET client side submit pipeline) . Now the hidden variable value can be used on the post-back to determine which link button has been clicked.
"Are there any other general things to check that could cause a button to require 2 clicks to post an event properly?"
Does it require two clicks on the control, or does it take accept a single click elsewhere on the screen, and then fire first time with a single click on the control?
I have my own (similar) issue with the Updatepanel where the first (expected) trigger does not fire and it seems that a single click elsewhere, and then the subsequent triggers fires first time (which totals 2 clicks)
[edit] Since you are working on this ATM, it may help me as well. Do you have a textbox with a trigger event on it? I do, and if I leave this blank (so that it does not fire) then there is no need for a second click.
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.
My ASP.NET form contains a collection of dynamically-created radiobuttons that are created and configured in the Page_Load event handler.
Normally, I process postback data in the Page_Load handler, using the condition:
if (IsPostBack)
However, since the controls that I need to access are created IN the Page_Load handler, the postback data from the previous rendering of the page is lost. To better illustrate the problem, here is an outline of the events as they occur:
1-Page_Load is invoked for the first time
2-An unknown number of radiobuttons are created dynamically
3-The radiobuttons are configured, based on information present on the server
4-The radiobuttons are added to the page's content
5-The user selects an option, and clicks the submit button
6-The Page_Load handler is invoked for the second time
7-The radio-buttons are added dynamically, exactly as before
8-The radio-button that the user checked is seemingly non-existant for processing
It seems like I need to be processing different parts of this in different event handlers. Is there an event that occurs after postback, but while the original radiobuttons are still accessible?
Check out the "Init" events...
http://msdn.microsoft.com/en-us/library/ms178472.aspx
My understanding of the order of page events is this:
Page : Load
Control : DataBind (for a GridView or whatever)
Control : Load
Control : Clicked (for a Button)
Page: PreRender
Control : PreRender
(There are lots of others - but these are the ones I'm interested in)
The important thing to notice here is that the button's click event comes after the gridview's bind event. If the button causes a change to the data, the GridView displays the old data. I could rebind the control in the PreRender event, but that seems totally ugly.
This must be a very common pattern (a button that updates data). How do I put this together so that the GridView binds to the data after the Button click changes it?
The answer was in the Button Click event, after the data has been changed, call DataBind() on the page to cause the GridView (and anything else that needs it) to rebind. I didn't realise you could do that.
Thank you Ocdecio & Mufasa - I would mark your answers as helpful, but I got no rep yet.
ASP.NET does, by default, lots of binding and rebinding. Rebinding after a click event is normal.
The only reason the button click event comes after GridView bind is because you programmed your page to do that . I don't see any problem in binding the control in the PreRender event, in fact that is the only way to take action after a control event (such as Button onclick).
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