Well, I found a solution myself (kind of a hack...).
This solution requires use of AJAX to capture the menu item onclick postback event, so it can be picked up client side in javascript before doing the actual postback when you click the menu item.
First, I override these functions that is defined by the Menu control
to ignore the menu popout in the mouseover event:
var activeMenuItem = null;
function Menu_HoverStatic(item) {
// Register the active item to be able to access it from AJAX
// initialize postback event
activeMenuItem = item
// Apply the style formatting on mouseover (colors etc).
// This was also called in the original Menu_HoverStatic function.
Menu_HoverRoot(item);
}
function Menu_Unhover(item) {
activeMenuItem = null; // This is the only difference to the original
var node = (item.tagName.toLowerCase() == "td") ?
item:
item.cells[0];
var nodeTable = WebForm_GetElementByTagName(node, "table");
if (nodeTable.hoverClass) {
WebForm_RemoveClassName(nodeTable, nodeTable.hoverClass);
}
node = nodeTable.rows[0].cells[0].childNodes[0];
if (node.hoverHyperLinkClass) {
WebForm_RemoveClassName(node, node.hoverHyperLinkClass);
}
Menu_Collapse(node);
}
// Then I added a renamed copy of the original `Menu_HoverStatic` function:
function Menu_ClickStatic() {
// Pick up the active menu item that is set in the
// overridden Menu_HoverStatic function.
// In the original, the item was input parameter.
var item = activeMenuItem;
// The rest is identical to the original Menu_HoverStatic.
var node = Menu_HoverRoot(item);
var data = Menu_GetData(item);
if (!data) return;
__disappearAfter = data.disappearAfter;
Menu_Expand(node, data.horizontalOffset, data.verticalOffset);
}
Then I snap up the onclick postback event in AJAX that is triggered by the menu. This must be done to cancel the onclick postback and display the menu popout instead.
// Get the Page Request Manager that provides all the .NET
var prm = Sys.WebForms.PageRequestManager.getInstance();
// Register postback event for asyncronous AJAX postbacks
if (prm) prm.add_initializeRequest(InitializePostback);
function InitializePostback(sender, args) {
var element = args.get_postBackElement();
//Check if the postback element is the menu
if (element.id == 'myMenu') {
// Name of the menu element that triggered is the postback argument
var postbackArguments = document.getElementById('__EVENTARGUMENT');
if (postbackArguments)
// Check on the menu item name to pick up only the menu items that shall
// trigger the popout (not the items that does an actual command).
if (postbackArguments.value == 'MenuTopItem1'
|| postbackArguments.value == 'MenuTopItem2'
|| postbackArguments.value == 'MenuTopItem3') {
// Abort and cancel the postback
prm.abortPostBack();
args.set_cancel(true);
Menu_ClickStatic(); // Call my own copy of the original function
return;
}
}
}
Note:
I found out the details about these functions by using the script viewer in Firebug.