Is there any window Focus event in XAmarin.Forms?

In my application having classes like A and B. If i am going to A to B then i am closing B and i need to update A page UI once A page is focued. I tried OnAppearing event but it is only calling once when class is loaded very first time. In Appcelerator having window foucs event, it is working fine. Is there any window Focus event in XAmarin.Forms?
Appcelerator Focus Event:

win.addEventListener('focus', function(e)
{
    setTimeout(function()
    {       
        Ti.API.debug('tab changed to ' + tabGroup.activeTab);        
    },100);
});