The data source for the picker view.
The data source must adopt the
UIPickerViewDataSource protocol and implement the required methods to return the number of components and the number of rows in each component.
Providing the Picker Data
UIPickerViewDataSource protocol must be adopted by an object that mediates between a
UIPickerView object and your application’s data model for that picker view. The data source provides the picker view with the number of components, and the number of rows in each component, for displaying the picker view data. Both methods in this protocol are required.