title: how to refresh a list of items based on the choice of the user (picker )
body: <p>hello i'm new to xamarin forms and i did some searching but didn't find much.
  i have a list of Items displayed on a page and i would like to refresh that list when the user choose from the picker.
   for example when the user chose monthly from the picker the list must be refreshed and show the items for this month i already have 3 functions functionDaily, functionMonthly, functionYearly that return ObservableCollection  but i don't know how to refresh the list when the user choose from the picker if somebody can help me Thanks </p>