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.
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 a custom asp.net user control which has an update panel in it. In this update panel i have all the controls and content that are shown to the user. Amongst these controls there are two textboxes, which have AutoPostback = true. This is because when their value is changed, the structure of the page changes accordingly. This works as required, but when I modify the two textboxes in quick succession, the first autopostback works while the second one doesn't fire. It seems that while it is doing the first postback, any other attempted postbacks will be ignored. How can I work around this?
This behavior is by design. The usual approach is to use UpdateProgress control that disables the user input on the page while the postback is in process.
Alternatively you could add your own onchange event handlers that call __doPostBack() more intelligently (by using timers etc.) to avoid this problem for your specific scenario. You could also try aborting any postback is process before submitting a new one.
A resource that might be useful: http://www.dotnetcurry.com/ShowArticle.aspx?ID=176
I am using entity framework 4.0 to bind a database object to a DetailsView on an ascx control. Within the DetailsView, I have a number of asp:panels that I'd like to show/hide depending on what's happening in that person's visit.
So, the first time through the page I'm setting panelA.Visible=false in the FormView_OnLoad event, and all is well - that panel is not output in the HTML. It listens to what I'm asking here.
Once I click submit and postback, I am again checking what's going on and setting panelA.Visibe=false in both FormView_OnLoad and EntityData_OnUpdating. But this time, when the page comes up panelA is showing.
I find that I can only hide that panel after postback by setting visible=false in DetailsView_PreRender, or by binding visibility to a public variable.
I'm thinking perhaps in the life cycle the DetailsView is binding again way toward the end, and throws away my visibility settings, even though they're not bound. So to show/hide panels within the DetailsView on postback, will I always have to set visibility on DetailsView_PreRender or after?
Am I on the right track here, or is something else resetting me at the last second?
Why can I set visibility the first time through the page but not postback?
You should always make final modification of your page structure after postback processing - that is the reason why PreRender event exists. Other possible event in your scenario can be handling DataBound event but better and more clear way is PreRender.
I've a page that has a series of web controls. One of these is a textbox with AutoPostBack turned off.
The way the page operates is that a button is clicked to save the form data. This button sits outside of the updatepanel.
So when I hit the save button the partial postback happens for the dropdownlist and after this postback has completed a full postback fires for the save button. However when the full postback fires the form data is returned to the state before the save button was clicked - i.e. my changes are removed.
I believe this could be to do with the viewstate being returned from the partial update and that viewstate not updating in the page before the full postback fires - or it getting corrupted.
Does anyone have any ideas?
Thanks.
Don't mean to sound negative but these scenarios are what made me give up "by the book" ASP.net AJAX. Learning jQuery /w simplistic ASP.net forms /w NO postbacks has lead me to build more useful and cooler UI experiences than what I had to battle to get working with update panels etc.
If you set UpdateMode="Conditional" and ChildrenAsTriggers="true" on your UpdatePanel, that will ensure the partial postback only executes when the DropDownList's postback event fires, not when the Button is clicked.
Thanks for the quick response! However I need the save buttons click event to fire too. The order in which the events fire is perfect:
dropdownlist changed event (partial)
save button click event (full)
The problem is the loss of form data after the partial postback.
Many thanks.
I've already posted a solution to this on another post. This simple code will ensure that your viewstate works with both the postback and partial postback.
Ideas for how to deal with viewstate when using ASP.NET AJAX and update panels
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.