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.NET Forum / Languages / C# / March 2008asp:DropDownList and Javascript
First - my MSDN Posting Alias isn't defined yet because the MSDN site is having problems, it came back with " We were unable to communicate with the Managed Newsgroups registration system". I have an ASP.NET website using C#. One page has two asp:DropDownList controls, one that controls the other. Think a car website (first select make, then model). I am using Javascript to populate the second list as the first one changes. The problem is that when I query these controls after the Submit button is pressed, it always returns back the first value of the original list contents of the second control. It seems to be ignoring what the Javascript did during runtime. So if the original list had "1", "2" and "3" in the list, and then the user changes list 1 to another option, which updates list 2 to have "4", "5" and "6" in the list. If the user clicks submit and the code queries the value of list 2, it will return "1". Hi Britain, From your description, you use javascritp to add some items into an ASP.NET dropdownlist, however, you found those added items disappear after the page be postback, correct? I think this is the expected behavior due to ASP.NET webserver control's control model. The control will construct its inner structure(and set properites) at server-side, all those status will be persited in Viewstate and render to client html. yes, you can modify the client-side html elements, however, after you postback the page, the page will recreate the control structure from viewstate, and your change at client-side will be lost. For your scenario, I think you can consider the following means: 1. You can consider add a hidden html field in page and add those items (you add into dropdownlist via script) into that field, and after postback, always checks this field and syncrhonize those items in the field to your dropdownlist's server-side item collection 2. You can consider use the ASP.NET ajax control (such as updatepanel) to provide postback processing without refreshing the page: #UpdatePanel Control Overview http://asp.net/ajax/documentation/live/overview/UpdatePanelOverview.aspx Best regards, Steven Cheng Microsoft MSDN Online Support Lead Delighting our customers is our #1 priority. We welcome your comments and suggestions about how we can improve the support we provide to you. Please feel free to let my manager know what you think of the level of service provided. You can send feedback directly to my manager at: msdnmg@microsoft.com. This posting is provided "AS IS" with no warranties, and confers no rights. -------------------- >From: "Britain Crooker" <britainc@community.nospam> >Subject: asp:DropDownList and Javascript >Date: Wed, 19 Mar 2008 21:53:09 -0400 >First - my MSDN Posting Alias isn't defined yet because the MSDN site is >having problems, it came back with " We were unable to communicate with the [quoted text clipped - 10 lines] >updates list 2 to have "4", "5" and "6" in the list. If the user clicks >submit and the code queries the value of list 2, it will return "1". Would it also be acceptable to update the first dropdown AutoPostBack=TRUE, then put in the SelectedIndexChanged event the code to update the dropdown items for the second control? > Hi Britain, > [quoted text clipped - 64 lines] >>updates list 2 to have "4", "5" and "6" in the list. If the user clicks >>submit and the code queries the value of list 2, it will return "1". Ok, what I described below MOSTLY seems to work, with one issue. If I disable JavaScript in my browser, then (obviously) the SelectedIndexChanged event will not fire until the user actually clicks the Submit button, rather than firing immediately after a new selection is made. Is there any way to determine which control initiated the PostBack? Basically, I would want the SelectedIndexChange event to not fire (or exit immediately) if the Submit button was pressed. I have found some sample code for determining the PostBox control, but they are all dependent on JavaScript. > Would it also be acceptable to update the first dropdown > AutoPostBack=TRUE, then put in the SelectedIndexChanged event the code to [quoted text clipped - 72 lines] >>>updates list 2 to have "4", "5" and "6" in the list. If the user clicks >>>submit and the code queries the value of list 2, it will return "1". Thanks for your reply Britain, Sure, you can use the "SelectedIndexChanged" event of the first dropdownlist to change the second(child) one's items. I didn't mention this means in previous message because I assume that you may want a non-postback approach(that will not refresh page). As for the new question you mentioned, I'm afraid Javascript is necessary here for you to provide additional information (whch control/elemente trigger the submit postback....). A plain html form submit will not contain any information about the source control who raise the postback/submit. Is there any particular requirement on client-side that can not use javascript? Best regards, Steven Cheng Microsoft MSDN Online Support Lead Delighting our customers is our #1 priority. We welcome your comments and suggestions about how we can improve the support we provide to you. Please feel free to let my manager know what you think of the level of service provided. You can send feedback directly to my manager at: msdnmg@microsoft.com. This posting is provided "AS IS" with no warranties, and confers no rights. -------------------- >Subject: Re: asp:DropDownList and Javascript >Date: Thu, 20 Mar 2008 11:15:33 -0400 >Ok, what I described below MOSTLY seems to work, with one issue. If I >disable JavaScript in my browser, then (obviously) the SelectedIndexChanged [quoted text clipped - 84 lines] >>>>updates list 2 to have "4", "5" and "6" in the list. If the user clicks >>>>submit and the code queries the value of list 2, it will return "1". Hi Britain, Have you got any progress on this issue? I'm still monitoring this thread and welcome to post here if there is anything else we can help.\ Sincerely, Steven Cheng Microsoft MSDN Online Support Lead Delighting our customers is our #1 priority. We welcome your comments and suggestions about how we can improve the support we provide to you. Please feel free to let my manager know what you think of the level of service provided. You can send feedback directly to my manager at: msdnmg@microsoft.com. This posting is provided "AS IS" with no warranties, and confers no rights. -------------------- >From: stcheng@online.microsoft.com ("Steven Cheng") >Organization: Microsoft >Date: Fri, 21 Mar 2008 01:31:05 GMT >Subject: Re: asp:DropDownList and Javascript >Thanks for your reply Britain, > [quoted text clipped - 78 lines] >>>> >>>> #UpdatePanel Control Overview http://asp.net/ajax/documentation/live/overview/UpdatePanelOverview.aspx >>>> Best regards, >>>> [quoted text clipped - 39 lines] >>>>>updates list 2 to have "4", "5" and "6" in the list. If the user clicks >>>>>submit and the code queries the value of list 2, it will return "1".
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