From Xojo Documentation

Property (As Date )
aiOSDatePicker.DefaultDate = newDateValue
DateValue = aiOSDatePicker.DefaultDate

Supported on Mobile (iOS).

The default date to display when DatePickerMode = Date or DateAndTime. Contains the selected date. By default, the current date and/or time is displayed (for date and time display modes).

Sample Code

Gets the selected date from the date picker:

Var selectedDate As Xojo.Core.Date
selectedDate = StartDatePicker.DefaultDate