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.
Related
I am trying to take advantage of the page lifecycle in Asp.NET so that I don't bind to my datasources more than I actually need to.
This has led to the following problem. I have an ObjectDataSource, GridView, and a button on my page. The button adds a record to the database, which should be picked up by the data source and presented on the Grid. The problem is that the item is not showing up on the gridview until I refresh the page.
I can solve the problem by calling GridView.DataBind() in my button's event handler, but this goes against what I understand about the .NET Page Lifecycle.
Based on this article, the lifecycle should be as follows:
In addition the article states that the Databinding event is "Raised after the control's PreRender event, which occurs after the page's PreRender event."
So, my button click event should fire first, during the Event Handling phase. It should add the record the database.
Next PreRender should be called on the controls.
Finally DataBind should be called on the controls, and the Grid should update to capture the new record.
Yet this doesn't seem to happen. What am I not understanding?
I think the issue is that your viewstate is not enabled on your GridView. This is what I experienced, but then I also had to call DataBind() on the GridView from the page PreRender event if the request was a postback to get the data updated in the GridView on postback.
Edit:
It would help to understand the issue and context better if you could post the source code of your page (aspx + codebehind). How and where do you connect your GridView to your datasource? Statically in markup or dynamically? Do you make any calls to page.DataBind()? ... These things may influence the behaviour of the GridView.
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.
I have two user controls on a page - UC1,UC2. Each usercontrol have a asp:button. Now if I click the any of the buttons the page post back. Now if I click the button of UC1 then the following happen.
Viewstate load for two user controls.
Page load called for two user controls.
The event handler of UC1 button is fired.
Now if user click on the UC1 button, I do not want to load the view state of UC2 user controls at server because the viewstate of UC2 is large.
The execution of UC1 is not dependent of UC2.
Please suggest how can I achive this.
Thanks!
What it sounds like your asking for is the ability to do partial postbacks. That is postbacks that only affect a portion of the page. There are a number of ways to accomplish this such as using the Microsoft provided AJAX controls (http://www.asp.net/ajax) or rolling your own with JQuery and web methods (this method however is stateless and should be expected as such). Specifically you will want to look at UpdatePanels and PostBack Triggers.
Hope this helps.
Do you know any drawback to add controls to a page on PreRender event?
please don't answer 'depends on your case' I'm talking in general:-)
The PreRender event happens after control events, so the control could not use any events.
If you for example add a Button in Page_PreRender, it's too late to hook up a Click event handler for it. At postack the button would not be recreated until after the click event had already been handled (and ignored).
Yes, see this link for the ASP.NET lifecycle:
http://msdn.microsoft.com/en-us/library/ms178472.aspx
I would recommend adding controls on the Init event as the new control would otherwise be cleared on any postbacks. This is as per https://web.archive.org/web/20210330142645/http://www.4guysfromrolla.com/articles/092904-1.aspx.
'Raised after all controls have been initialized and any skin settings have been applied. Use this event to read or initialize control properties.'
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