When activities are deserialized from an external items source such as the Infragistics.Scheduler.DataSource.ScheduleListDataSource.AppointmentItemsSource, the value of some other instance's RecurrenceId property is checked against the value of this property to determine whether that instance is a member of this activity's recurrence.
When no value is explicitly assigned, a GUID is generated and the string representation thereof is used as the activity's identifier.
Target Platforms: Android 4.4+, iOS 8+
Development Environments: Visual Studio 2015+, Visual Studio for Mac Preview, Xamarin for Visual Studio 4.2+