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ASP.Net/C# - How to get value of a regular HTML Select List Box in code behind?

Posted on 2008-06-25
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3,858 Views
Last Modified: 2012-08-14
Hello all I could really use some help here.  I have a ASPX page that has a regular select list on it where the user can add and remove items via javascript.  I need to in my code behind on a save loop through each value that was entered into that select list to create a semi-colon seperated string.  Then the same coming back into the page I need to parse through the values and add to the list box.  I know how to handle the for loop for the coming back with a string split.  I just need to know how to add the item to the select list HTML.  Any help would be much appreciated.  Attached is the code from the page.
<script type="text/javascript" language="javascript">
	function remove()
	{
		var list = window.document.getElementById('myList');
		var keepLooking = true;
		while ( keepLooking ) {
			list.remove( list.options.selectedIndex );
			if ( list.options.selectedIndex < 0 ) {
				keepLooking = false;
			}
		}
	}
	
	function add()
	{
		var list = window.document.getElementById('myList');
		var tbox = document.getElementById('myText');
		var tval = tbox.value;
        var newOpt = document.createElement('option');
        var txt = document.createTextNode(tval);
        newOpt.appendChild(txt);
        newOpt.setAttribute('value', tval);
        //newOpt.text = tval;
        //newOpt.value = tval;
        list.appendChild(newOpt);
	}
</script>
 
<select id="myList" name="myList" size="10" style="width:200px;"></select>
<a href="javascript:remove();">Remove</a><br />
<input type="text" id="myText" value="" style="width:200px;"/>
<a href="javascript:add();">Add</a>

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Question by:sbornstein2
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8 Comments
 
LVL 21

Accepted Solution

by:
naspinski earned 250 total points
ID: 21864804
Instead, why don't you make this an asp:dropdownlist and change the javascript to accommodate the newly generated IDs (view source).  Ass the asp controls just make an html drop list anyways, jsut takes care of a lot of the footwork of getting it to the backend.
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Author Comment

by:sbornstein2
ID: 21864937
ya that is what I was thinking but im not sure how to do that.  Do I use just the name of the listbox? and also the other problem is I just need to make sure it does not post back.
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LVL 21

Expert Comment

by:naspinski
ID: 21864975
If it does not postback, there is no way to get the codebehind (c#) the value, as that is server side.

So you need a postback... you could use an ajax asp:updatepanel for an asynch postback.

Also, to get the asp-made ids, just run your page, go into your browser and view source.  Then find the dropdowns and you can see the ID that asp made for them... use those.
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Author Comment

by:sbornstein2
ID: 21865002
ok so ya this would work and then I can use:

StringBuilder sb = new StringBuilder();
            foreach (ListItem item in lstBulletPoints.Items)
            {
                try
                {
                    sb.Append(item.Text.ToString() + ";");
                }
                catch (Exception)
                {
                    // ignore
                }
            }
that will create my list.

Can that ID ever change though and is there a better way to use like a client id or something
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LVL 21

Expert Comment

by:naspinski
ID: 21865033
The ID will never change.  It is a bit of a pain, but in order to allow both server and client-side scripts to work on the same objects, you have to coax them into working sometimes.
0
 
LVL 39

Assisted Solution

by:Pratima Pharande
Pratima Pharande earned 250 total points
ID: 21865043
<select id="myList" name="myList" size="10" style="width:200px;" runat="server"></select>

To add values thorugh asp.net

  myList.Items.Add("3");
                    myList.Items.Add("4");
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LVL 21

Expert Comment

by:naspinski
ID: 21865074
wow... i feel like an idiot since I didn't even think of making it a server control :P  good call pratima

Just have to make sure it is inside of a form tag that is also runat="server"
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Author Closing Comment

by:sbornstein2
ID: 31470523
both were helpful thanks guys.  I might use AJAX and a server control instead but nevertheless thanks for the help and awesome info
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