ExtGridView

<script type="text/javascript" src="js/CollapseExpand.js"></script>

// Adds the expand all / collapse all button
function AddExpandCollapseAllButton(strMainTableID,strHiddenFieldID)
{
    var objMainTable = document.getElementById(strMainTableID);
    var objHiddenField = document.getElementById(strHiddenFieldID);
    
    var strButtonLink = '<a href="#" onclick="ExpandCollapseAllButtonClick(\'' + strMainTableID + '\',\'' + strHiddenFieldID + '\');">';
    
    if (objHiddenField.value == 'True')
    {
        strButtonLink += '<img src="images/expand.gif" alt="+" border="0" />';
    }
    else
    {
        strButtonLink += '<img src="images/collapse.gif" alt="-" border="0" />';
    }

    strButtonLink += '</a>';
    objMainTable.rows[0].cells[0].innerHTML = strButtonLink;
}

// Expands or collapses the tables
function ExpandCollapseAllButtonClick(strMainTableID,strHiddenFieldID)
{
    var objMainTable = document.getElementById(strMainTableID);
    var objHiddenField = document.getElementById(strHiddenFieldID);
    
    var strButtonLink = '<a href="#" onclick="ExpandCollapseAllButtonClick(\'' + strMainTableID + '\',\'' + strHiddenFieldID + '\');">';
    
    if (objHiddenField.value == 'True')
    {
        strButtonLink += '<img src="images/collapse.gif" alt="-" border="0" />';
        objHiddenField.value = 'False';
    }
    else
    {
        strButtonLink += '<img src="images/expand.gif" alt="+" border="0" />';
        objHiddenField.value = 'True';
    }

    strButtonLink += '</a>';
    objMainTable.rows[0].cells[0].innerHTML = strButtonLink;
    
    ExpandCollapseAll(objMainTable,objHiddenField,false);
}

// The expand all / collapse all function
function ExpandCollapseAll(objMainTable,objHiddenField,blnNoHeader)
{
    if (objMainTable != null)
    {
        try
        {
            var expandClass = objMainTable.attributes.getNamedItem('expandClass').value;
            var collapseClass = objMainTable.attributes.getNamedItem('collapseClass').value;
            var expandText = objMainTable.attributes.getNamedItem('expandText').value;
            var collapseText = objMainTable.attributes.getNamedItem('collapseText').value;
            
            var i = 0;
            if (blnNoHeader == false)
            {
                i = 1;
            }
            
            for (i; i < objMainTable.rows.length; i+=2)
            {
                var row = objMainTable.rows[i];
                var row1 = objMainTable.rows[i+1];
                var ihExp = row.cells[0].getElementsByTagName('input').item(0);
                var ctl = row.cells[0].getElementsByTagName('a').item(0);

                if (!ihExp || !ctl)
                {
                    continue;
                }

                //if (row1.style.display == 'none')
                if (objHiddenField.value == 'False')
                {
                    row1.style.display = '';
                    ctl.innerHTML = collapseText;
                    ctl.className = collapseClass;
                    ihExp.value = '1';
                }
                else
                {
                    row1.style.display = 'none';
                    ctl.innerHTML = expandText;
                    ctl.className = expandClass;
                    ihExp.value = '';
                }
            }
        }
        
        catch(err)
        {
        }
        
        var objTables = objMainTable.getElementsByTagName('TABLE');
        
        for (var i = 0; i < objTables.length; i++)
        {
            ExpandCollapseAll(objMainTable.getElementsByTagName('TABLE')[i],objHiddenField,false);        
        }
    }
}

<asp:HiddenField ID="hidCollapsed" runat="server" Value="True" />

'adds a expand all / collapse all feature
Dim strScript As New StringBuilder
strScript.AppendLine("<script type=""text/javascript"">")
strScript.AppendLine("AddExpandCollapseAllButton('usercontrolname_maingridviewname','usercontrolname_hidCollapsed');")
strScript.AppendLine("</script>")

Page.ClientScript.RegisterStartupScript(Me.GetType(), "AddClientSideExpandCollapseAllButton", strScript.ToString