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Accessing asp:DropDownList.SelectedItem.Text from Client Side

Posted on 2004-10-11
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Last Modified: 2006-11-17
I am using ASP.NET to create a page with a dropdownlist box that is used to capture the name of a table (or view) from the user.

Given this info, I want to go to a particular web page to display records for this table.

When I try to retrieve the text that indicates the appropriate table/view entered into a asp:DropDownList control I get an "Object required" error.

I realize that I am trying to access a server control from the client and there are problems associated with to do this. This site has suggested that:

tablename= document.forms(0).getElementById('lstDropDown').SelectedItem.Text

might work from the client-side. But, this approach comes back and says "Error: Syntax".

Is there anyway to do this? I have a server-side menu control that has triggered client-side code. I know what I want to do, but don't know the table to do it to.
Any thoughts?

 

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Question by:gbmcneil
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LVL 15

Expert Comment

by:praneetha
ID: 12278506
var selNum=document.getElementById("lstDropDown").selectedIndex;
var selCategory=document.getElementById("lstDropDown").options[selNum].text;//value..

try that
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Author Comment

by:gbmcneil
ID: 12279243
Praneetha -

Your codes works fine. Thanks very much for your help. Here is the equivalent embellished VBScript to get the job done:

selNum=document.getElementById("lstDropDown").SelectedIndex
      tablename=document.getElementById("lstDropDown").Options(selNum).text
If Trim(tablename) = "Select a tablename..." Then
            MsgBox "You cannot add a new record until you have first selected a tablename.", 16, "Error Message"
      End If
      If Trim(tablename) = "Customers" Then
            window.location.href = "http://bflat77/DemoApp/AddNewCustomers.aspx"
      End If

But, can you tell me why I just can't say the following (shown below)? It seems it would be more straight forward.

tablename = document.lstDropDown.SelectedItem.Text    

It comes back and gives the error message "Error: Object doesn't support this property or method: 'document.lstDropDown' when this seemingly more obvious syntax is used.








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LVL 15

Expert Comment

by:praneetha
ID: 12279271
i guess since dropdownlist does not have this properties in javascript..

.SelectedItem.Text    
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LVL 6

Accepted Solution

by:
ryerras earned 125 total points
ID: 12279701
You can not write directly document.lstDropDown.SelectedItem because, the drop down is a server control. So, you can not specify it that way, because your web form contains the drop downlist. So, its a hierarchy, document contains Form1, then Form1 contains dropdown control. But if you use getElementByID(), it will search the entire hierarchy to find the element. So, the correct syntax to access the drop down list is

 document.Form1.lstDropDown, assuming Form1 is the id of your form, the alternative is document.forms[0].lstDropDown, here you do not have to specify the form id.

To access any item inside the drop down, you need to specify the index, since the items inside the drop down are more like array elements, so to access any type of element, you should use document.forms[0].lstDropDown.options[0].text.

By the way, if your drop down list is a server control, its always better to use getElementbyId(), sometimes the asp.net changes the id of the control after it renders it as an html control. Remember all the server controls are eventually have to be mapped to a corresponding html control to actually be used in web pages. The html control for asp.net dropdown list is "Select". If you look at the source, you can easily see that
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LVL 6

Expert Comment

by:ryerras
ID: 12279753
I need to edit one sentence in my previous post

>>You can not write directly document.lstDropDown.SelectedItem because, the drop down is a server control.So, you can not specify it that way, because your web form contains the drop downlist. So, its a hierarchy, document contains Form1, then Form1 contains dropdown control.

its the same case for type of control, html, or server controls , it doesnt matter. Controls are placed on forms. A document contains a Form. So its like

document->form->control



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Author Comment

by:gbmcneil
ID: 12280670
Hello ryerras -

Gee, I'm impressed. Thanks for taking the time to explain that to me. Appreciate it.
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LVL 6

Expert Comment

by:ryerras
ID: 12281009
Where are my points then :d, Just kidding. Glad to be a help
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Author Comment

by:gbmcneil
ID: 12283572
Am I supposed to be the one that awards the points?

Both you (ryerras) and praneetha were great! Maybe I should split the trophy in half.

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LVL 6

Expert Comment

by:ryerras
ID: 12285875
Yeah, if you think you want to award the points to both, you should pick one as Accepted answer and other as Assisted answer. You should see them somewhere on the tabs besides the comments.
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