GridView doesn't reload their data

I have a GridView and I only can modify their attributes like ItemWidth, ItemHeight, Source, etc. when the page is created. After that, the grid object has the modifications in memory but the screen doesn't show it.

I am using MVVM with XLabs and I try to update the ItemSource with NotifyPropetyChange from ViewModel.

I tried to update the source invoking the UIMainThtread using Xamarin.Forms.Device.BeginInvokeOnMainThread but not works.

Some idea?