Sometimes we have to capture page close event or navigation event to alert users. For example, Alerting user for navigating away from input page without saving it. Check this java script code..

window.onbeforeunload= function(){
if((window.event.clientX<0) || (window.event.clientY<0))
    {
      event.returnValue = "Are you sure you want to navigate away from this page? You haven't saved this form.";
    }
};

This code works only in Ie6/7. And also keep in mind, we can never catch the browser close event for 100%. For example, what if the user kills the browser process or shut down OS.

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)

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

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.

Here is sample code for TextBox Validation to allow Numbers only.

In Code behind add this function to "onkeyup" event for TextBox

Some times we need to auto-refresh page after few seconds. you can do it with Meta Refresh tags

Where content '180' is the number of seconds.

Another approach is by addding HTTP header..

Here is sample code for adding tooltip to DropDownList. The key here is adding "title" attribute to the list items in DataBound event.

<asp:DropDownList ID="DropDownList1" runat="server" ondatabound="DropDownList1_DataBound">
</asp:DropDownList>

protected void DropDownList1_DataBound(object sender, EventArgs e)
{
    DropDownList ddl = sender as DropDownList;
    if (ddl != null)
    {
        foreach (ListItem li in ddl.Items)
        {
           li.Attributes["title"] = li.Text; // setting text value of item as tooltip

        }
    }

}

For a Textbox with Read-only property set to true, text is not be posted back to the server side.

From MSDN..

The Text value of a TextBox control with the ReadOnly property set to true is sent to the server when a postback occurs, but the server does no processing for a read-only text box. This prevents a malicious user from changing a Text value that is read-only.

To set a Textbox read-only and keep the text on post back, use the following code..

We can get it from the Request object as shown below…

  TextBox1.Text = Request[TextBox1.UniqueID]; //Another approach… 

  TextBox1.Text = Request.Form[TextBox1.ClientID.Replace("_", "$")];