I'm writing an ASP.Net webform with some DropDownList controls on it. Then user changes selected item in one of dropdowns, ASP.Net doesn't seem to handle SelectedIndexChanged event until form is submitted with a 'Submit' button click.
How do I make my dropdowns handle SelectedIndexChanged instantly?
P.S. It's a classic question I have answered too many times, but it seems no one asked it before on stackoverflow.
Setting the AutoPostback property to true will cause it to postback when the selection is changed. Please note that this requires javascript to be enabled.
You need to set the AutoPostBack property of the list to true.
Also, if you're populating the contents of the drop down list from the code behind (getting the contents of the list from a database, for example) - make sure you're not re-binding the data in every postback.
Sometimes people are caught out by binding the drop-down in the page load event without putting it in an If Not IsPostBack. This will cause the event not to fire.
The same is also true of repeaters and ItemCommand events.
if you are populating the dropdown list during page load then each time the page postback it will reload the list thus negating your postback method.
you need to be sure to load the dropdownlist only if (!ispostback)
Set the AutoPostBack property of DropDownList to true.
Related
I have a dropdownlist control and a text box control in asp.net. dropdownlist is getting data from database. suppose some data are x-ray,USG,MRI and their value are 100,200,300. So if i select x-ray from the dropdown i want it's value 100 binds at the textbox without page refresh. How can i do this??? Please Help.
Using .net, to have something happen on the server side when something is selected from DropDownList, having property AutoPostBack=true is required. This means when you change the SelectedIndex, the page refreshes (postback), then the SelectedIndexChanged event is fired.
Theres a few approaches. In your page_load event, put everything you want to happen on the first page load in If Not IsPostBack Then ... End If block. Then when a PostBack happens, like DropDownList_SelectedIndexChanged, the code in If Not IsPostBack Then won't happen, because it IS a postback.
The above approach still has a page reload, but you can choose what happens when its this type of PostBack page reload. You may have javascript thats re-firing, though...
The second approach would be to have no postback event happen from the dropdownlist, and handle the Binding of the selected item in DropDownList to the TextBox with javascript.
How can I make a dropdownlist with no postback - I have a dropdownlist which has code in selectedindexchanged
Basically for every indexchanged the code will connect to sql and get values then populate textboxes with values.
Here is my code
<asp:DropDownList ID="ddlSalesOrg" runat="server" Style="width: 200px;"
AutoPostBack="true" />
I want that the selectedindexchange should get hit, but it should NOT cause a full postback. If I set the AutoPostBack to false, then it won't hit selectedindexchange at all
You must choose - do you want postback or not. You can't set AutoPostBack="true" and after that stop the post backs.
If you just don't need full postback - use UpdatePanel for partial page update.
I dont get you question, do you want avoid the postback and also have the funcionality of vb/C# on every indexchanged?
Then your solution were AJAX all this time.
At this time I supose you have more knowledge about this.
But only for the register.
When you write something in the codebehing of ASP in response to an event, there you MUST be a postback (or partial postback) to achieve that code.
If you stop the postback abiously (as you said) these code is not achieved.
If you want to avoid the postback and also get some databind functionality (or any server side functionality) then you can disable the postback, handle the event in javascript, and call some AJAX function to make the databind.
key words for your next google search: ajax, dropdownlist,asp
Good luck to the next guy who has this problem.
You need to set the AutoPostBack property of the list to true.
Also, if you're populating the contents of the drop down list from the code behind (getting the contents of the list from a database, for example) - make sure you're not re-binding the data in every postback.
Sometimes people are caught out by binding the drop-down in the page load event without putting it in an If Not IsPostBack. This will cause the event not to fire.
The same is also true of repeaters and ItemCommand events.
Respected sirs
I am using a DropDownList control and binding it to a LinqDataSource.
According to the selection of the mentioned DropDownList, I need to bind another DropDownList control.
I have handled the SelectedIndexChanged event for first DropDownList. When this SelectedIndexChanged occurs, page is getting refreshed. To prevent page from beend refreshed, I am using an UpdatePanel control. But, still the second DropDownList not loading.
Please give me a solution.
Thanks
Saravanaa
Place the second DropDownList inside the UpdatePanel.
You may want to consider using CascadeDropDown too.
I forgot to mention this asp.net 2.0.
The user control has a unique id and it is loaded in the PageLoad event.
The user control is loaded into a panel and the panel is inside of a webpart.
The dropdown has autopostback set to true.
EnableViewState = true on the dropdown.
The ListItems are created in the dropdowns pre-render event method.
This is why I don't understand why it is not firing, the dropdown is the only thing that causes postback on this user control.
The event methods for the dropdown should occur since the user control is loaded in the page load method on postback again right?
Make sure there is no OnLoad or PageLoad event that is rebinding the datasource of the dropdown list. Rebinding the data with a new set of data may cause the clickhandler to not ever get executed.
make sure you have if (!Page.IsPostBack) around dropdownlist.datasource = and dropdownlist.databind()
I am not sure if this is your problem, but it is the most common.
Try with EnableViewState set to
true for the DropDownList
If the ViewState is set to false, on post back the selected Index gets back to default which is normally the first Item. First item, if selected, does not cause SelectedIndexChange event to fire
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).