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Vijay Kodali
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Add, Delete Items in DropDownList, ListBox using Javascript

I have seen lots of questions in Asp.Net forums for adding/deleting items in drop down list or list box using JavaScript. Here is the code...

<asp:DropDownList ID="DropDownList1" runat="server" Width="182px"> 
<asp:ListItem value="1" Text ="Approve"></asp:ListItem> 
<asp:ListItem value="2" Text ="Accept"></asp:ListItem> 
<asp:ListItem value="3" Text ="Test1"></asp:ListItem> 
<asp:ListItem value="4" Text ="Test2"></asp:ListItem> 
</asp:DropDownList> 

<input type="button" value="Remove selected item" onclick="JavaScript: DeleteItem();" /> 
<input type="text" id="ddlText" name="ddlText" /> 
<input type="text" id="ddlValue" name="ddlValue" /> 
<input type="button" value="Add item" onclick="JavaScript: AddItem();" /> 
<input type="hidden" id="ddlElements" name="ddlElements" runat="server" /> 
<asp:Button ID="Button1" runat="server" Text="Button" />
    <script type="text/javascript"> 
    function DeleteItem() 
    { 

        var dropDownListRef = document.getElementById('<%= DropDownList1.ClientID %>'); 
        var optionsList = ''; 

        if ( dropDownListRef.value.length > 0 ) 
        { 
            var itemIndex = dropDownListRef.selectedIndex;
       if ( itemIndex >= 0 ) 
            dropDownListRef.remove(itemIndex); 
        } 
        else 
        { 
            alert('Please select an item'); 
            dropDownListRef.focus(); 
            dropDownListRef.select(); 
        } 
          

        for (var i=0; i<dropDownListRef.options.length; i++) 
        { 
        var optionText = dropDownListRef.options[i].text;
        var optionValue = dropDownListRef.options[i].value; 
     
        if ( optionsList.length > 0 )
            optionsList += ';'; 
            optionsList += optionText; 
            optionsList += ';'; 
            optionsList += optionValue; 
        } 
        document.getElementById('<%= ddlElements.ClientID %>').value = optionsList; 
    } 


    function AddItem() 
    { 

        var dropDownListRef = document.getElementById('<%= DropDownList1.ClientID %>'); 
        var ddlTextRef = document.getElementById('ddlText'); 
        var ddlValueRef = document.getElementById('ddlValue'); 
        var optionsList = ''; 

        if ( ddlTextRef.value !="" && ddlValueRef.value!="" ) 
        { 
            var option1 = document.createElement("option"); 
            option1.text= ddlValueRef.value; 
            option1.value= ddlTextRef.value ; 
            dropDownListRef.options.add(option1); 
        } 
        else 
            alert('Please enter values'); 
          
        for (var i=0; i<dropDownListRef.options.length; i++) 
        { 

        var optionText = dropDownListRef.options[i].text;
        var optionValue = dropDownListRef.options[i].value; 
          
        if ( optionsList.length > 0 )
        
            optionsList += ';'; 
            optionsList += optionText; 
            optionsList += ';'; 
            optionsList += optionValue; 
        } 
            document.getElementById('<%= ddlElements.ClientID %>').value = optionsList; 
       
    } 

</script>

In Code behind Page_Load, add following code..

if (IsPostBack)
{
    DropDownList1.Items.Clear();
    string[] DropDownListArray = ddlElements.Value.Trim().Split(';'); 
    
    for (int i = 0; i < DropDownListArray.Length; i = i + 2)
    {
        string itemText = DropDownListArray[i];
        string itemValue = DropDownListArray[i + 1]; 
        DropDownList1.Items.Add(new ListItem(itemText, itemValue));
    }

}

string optionsList = string.Empty; 
for (int i = 0; i < DropDownList1.Items.Count; i++)
{
   string optionText = DropDownList1.Items[i].Text;
   string optionValue = DropDownList1.Items[i].Value;
          
    if (optionsList.Length > 0) 
      
    optionsList += ";";
    optionsList += optionText;
    optionsList += ';';
    optionsList += optionValue;
}

ddlElements.Value = optionsList; 

Update:  Client-side changes to a DropDownList/ListBox are not persisted server-side, so any changes made will be lost if a PostBack occurs. Added server-side persistence to code. (Thanks to tip form NC01)

 


Tags:
Posted by vijay on Friday, December 14, 2007 9:40 PM
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Session timeout error in Asp.Net

1.) We were facing timeout issue on one of our servers. Web.config settings had no effect on the time out.

2.) I have set the session to last 24 hours with this statement in my web.config:

		
	
		<sessionState mode="InProc" timeout="720"/>	
	

     But the session still ends after 20 min of inactivity. What am I missing here?

I saw similar type of questions frequently in Asp.Net forums. Here is a post to help those

What is Session State?

ASP.NET session state enables you to store and retrieve values for a user as the user navigates ASP.NET pages in a Web application. In order to preserve server memory, ASP.NET implements a rolling timeout mechanism which discards the session information for a user if no request is seen within the timeout period (default 20 minutes which is reset with each request).

You would also have to setup session timeout in IIS in addition to webconfig settings.

In IIS6 change the session timeout setting by going to:
'Configuration' Button -> 'Options' Tab -> Tick Enable Session state, increase value from default 20 mins to desired value

In IIS7 change the session timeout setting by going to:

Features View pane –> Application Development – >Sessions state

IIS 7-1 

IIS 7-2

Don’t see Session state icon in IIS 7? Check this blog post

http://blogs.msdn.com/webdevtools/archive/2006/09/18/761206.aspx

Here are some other reasons for Session loss..

1.) IIS worker process restart or Application Pool recycle.(Check the System logs)

2.) Application Domain restart due to Antivirus scans or changes in Config files.

 

Please leave a comment.


Posted by vijay on Sunday, December 02, 2007 8:37 PM
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