I have already researched this topic to death and found people posting the exact same question on a number of websites including right here in stackoverflow.
I have
It is very easy. Defines delegate TextField (UITextFieldDelegate) in the .h in the viewDidLoad .m
myTextField.setDelegate = self;
In the same viewDidLoad associates the datePicker to myTextField.
myTextField.inputView = myDatePicker;
You can also do anime, but this is the easiest way.