Restore the lost focus of Auto post back controls in asp.net update Panel control

Problem:
We put  autopostback controls like textbox, DropDownList controls inside in update panel to reducing the flickering of the Page.but when user uses tab for entering the details  the focus of the control losts. Web site users who prefer to use keyboard need to use mouse to activate appropriate input box or press TAB multiple times.

Solution:

Step 1:

Save following in js file give any name to it (like MyUpdatePanelFocus.js)

var lastFocusedControlId = "";

function focusHandler(e) {
    document.activeElement = e.originalTarget;
}

function appInit() {
    if (typeof (window.addEventListener) !== "undefined") {
        window.addEventListener("focus", focusHandler, true);
    }
    Sys.WebForms.PageRequestManager.getInstance().add_pageLoading(pageLoadingHandler);
    Sys.WebForms.PageRequestManager.getInstance().add_pageLoaded(pageLoadedHandler);
}

function pageLoadingHandler(sender, args) {
    lastFocusedControlId = typeof (document.activeElement) === "undefined"
        ? "" : document.activeElement.id;
}

function focusControl(targetControl) {
    if (Sys.Browser.agent === Sys.Browser.InternetExplorer) {
        var focusTarget = targetControl;
        if (focusTarget && (typeof (focusTarget.contentEditable) !== "undefined")) {
            oldContentEditableSetting = focusTarget.contentEditable;
            focusTarget.contentEditable = false;
        }
        else {
            focusTarget = null;
        }
        targetControl.focus();
        if (focusTarget) {
            focusTarget.contentEditable = oldContentEditableSetting;
        }
    }
    else {
        targetControl.focus();
    }
}

function pageLoadedHandler(sender, args) {
    if (typeof (lastFocusedControlId) !== "undefined" && lastFocusedControlId != "") {
        var newFocused = $get(lastFocusedControlId);
        if (newFocused) {
            focusControl(newFocused);
        }
    }
}

Sys.Application.add_init(appInit);

Step 2: Do the following setting in aspx page

    <asp:ScriptManager ID="c_scriptManager" runat="server">
        <Scripts>
            <asp:ScriptReference Path="~/MyUpdatePanelFocus.js" />
        </Scripts>
    </asp:ScriptManager>

That's it you have done it!!!!