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).
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 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 a gridview inside a User Control which is being filled with data from a data source dynamically. One of the things I need to support is switching a non-data-bounded column from checkbox column to radiobutton column dybamically.
everything's cool when I create the columns for display, but when I try to add an event to the CheckChanged (or Click) of the columns, the events doesn't fire - Not at AsyncPostBack and not at full postback. Moreover, the AutoPostBack is set to true and the checkboxes and radiobuttons do fire the postback, but not their events.
I don't think it's relevant, but the loaded usercontrol is in a ModalPopUpExtender from AjaxToolkit and it is being showed at server side (using a dummy button, and a clickable button ith a server side event on click). Also, all the ModalPopUpExtender controls are inside of an UpdatePanel, and only the clickable button is not.
thanks in advance.
I'm not sure if it'll work using Ajax and ModalPopUpExtender but I think you need to handle it in the OnRowCommand event of grid.
So, the column of the checkboxes should have been added in a static sort of way (declare the column and the checkboxes/radiobuttons in html) - the page would register to the events, or needed to be registered in PreRender of the GridView, after acknowledging that they were added during an Ajax postback... the latter is the best way... but for those who have no time to debug, first way is better. see also:
http://www.codeproject.com/KB/custom-controls/asp-ajax-custom-controls.aspx
I have a datalist and want to dynamically add buttons to it. I am using the OnItemCommand datalist event and setting the CommandName/ CommandArgument attributes of the button.
However I am having trouble with handling the button click - does not seem to fire.
It works when I declared a button on the aspx page, but not for buttons that are dynamically created.
I hope this makes sense, and any help would be great.
Thanks
You can only create dynamic controls on PreInit or Init if you want to handle associated events. Otherwise, on postback, they won't exist at the moment of event handling and because of that, your handler method won't be called.
Internet is full of resources about how to handle dynamic controls. Let me know if you need any reference.
Assume I have an asp:GridView with some customer information. On that page I also have a button which allows me to add a new user to the GridView. When I add the click the user, I databind the gridview again in the button click. Correct me if I am wrong, but if the asp.net lifecycle or at least part of it is in the following order:
page_load
Hookup event handlers such as my button click
page_preRender
Does this mean that if I put the databinding for the gridview in preRender, that is the only place I need to worry about calling it. I can remove it from the button click. This is what I think, but I am not sure if my thinking is correct, so I would like some more insight as to the benefit of putting code in PreRender as opposed to PageLoad
By PreRender, you assume that most logic in the page that would affect the binding result has been completed (usually in Page_Load, but anywhere earlier really).
Controls in the .Net framework by default do their binding in the PreRender event (makes sense, bind to the datasource at the last possible moment...could be that you changed the data 400 times earlier in the lifecycle). Here's the full layout of the 2.0 lifecycle for reference.
PreRender - Before this event occurs:
The Page object calls EnsureChildControls for each control and for the page.
Each data bound control whose DataSourceID property is set calls its DataBind method. For more information, see Data Binding Events for Data-Bound Controls later in this topic.
The PreRender event occurs for each control on the page. Use the event to make final changes to the contents of the page or its controls.