[WinPhone] DatePicker bug/best practice

Not sure if this is a proper bug, or should merely be a note of caution/best practice.

I've confirmed this in WinPhone under XForms 1.4.4.6392, but NOT Android. I suspect this is because Android uses a pop-up, while WinPhone displays an interstitial page (modal?) and the OS treats modals like proper pages.

To replicate this, add a page with a DatePicker. Set the date of the DatePicker in an overridden OnAppearing method. You cannot change the date as the OnAppearing method will be called every time you select a new date.

This is what you OnAppearing should look like:

protected override void OnAppearing()
{
    base.OnAppearing();

    MyDatePicker.Date = DateTime.Today;
}

Every time you change the date, it will reset to today.

The issue is, we should be setting data after the controls have loaded. The lack of a Loaded method means OnAppearing is the closest analogue. This bug means OnAppearing is an unreliable tool for avoiding potential race conditions of loading as you can easily create other problems.