UIDatePicker expand & collapse

Thanks, guywithmazda, your suggestion turns out to be the right general direction.

To back track a bit, the Apple recommended method to make this happen is to put everything in a tableView. So in one cell you have a label showing a picked date and then the cell just below the datePicker that gets hidden by hiding/unhiding the cell as needed. I was halfway into trying that when someone on stackoverflow suggested an alternate way is to put a height constraint on the datePicker, get an IBOutlet of that constraint into viewController and dynamically set the constraint to zero (hide) or X (open) as needed. It actually works and here is the code.

First, I have a relatively generic form in my viewController continaing: a "label" for the date to be picked (see details below), followed by the datePicker, followed by a number of other text fields below. I set both a height constraint for the datePicker and a top/bottom constraint between the date label & the datePicker. Then ctrl-drag each of these constraints into the viewController.swift file like so:

@IBOutlet weak var datePickerHeight: NSLayoutConstraint!
@IBOutlet weak var datePickerMarginTop: NSLayoutConstraint!

I have a state variable defined within the viewController class & some constants specifying the dimensions I want:

var datePickerOpened: Bool = false    // state variable
let datePickerHeightOpened: CGFloat = 214
let datePickerHeightClosed: CGFloat = 0
let datePickerMarginTopOpened: CGFloat = 0  // 18 (see below)
let datePickerMarginTopClosed: CGFloat = 0
let animateTimeStd: NSTimeInterval = 0.5
let animateTimeZero: NSTimeInterval = 0.0

Then I have this function defined to handle opening & hiding the datePicker:

func showDatePicker(show: Bool, animateTime: NSTimeInterval) {
        // set state variable
        datePickerOpened = show

        // this makes the datePicker disappear from the screen BUT leaves the space still occupied
        // this is not strictly necessary but it will make the appearance more tidy
        self.datePicker.hidden = !show

        // animate the datePicker open/hide - this is the where the constraints are modified
        UIView.animateWithDuration(animateTime, animations: {
      
            // toggle open/close the datePicker
            self.datePickerHeight.constant = (show ? self.datePickerHeightOpened : self.datePickerHeightClosed)
      
            // toggle open/close the datePicker top margin
            // as it turns out for me, it looked better in my set up to have top margin zero all the time but I'm leaving the code here in case I need it later
            self.datePickerMarginTop.constant = (show ? self.datePickerMarginTopOpened : self.datePickerMarginTopClosed)
      
            // this I understand tells the view to update
            self.view.layoutIfNeeded()
       })
}

Then in viewDidLoad(), ie in initial view load, I tell the datePicker to hide & do it without animation (otherwise there is an annoying flicker):

showDatePicker(false, animateTime: animateTimeZero)

For me, the "label" showing the date picked is actually a button. At the outset I just thought that would be the easiest way to make a datePicker open/hide. I could just as well have used an actual UILabel or a UITextField. Just the mechanism to invoke the datePicker would be somewhat different I guess. So my IBAction for that button is simply the following which uses the datePickerOpened state variable to toggle and specifies the open/hide to be animated:

@IBAction func dueDateAction(sender: AnyObject) {
    showDatePicker(!datePickerOpened, animateTime: animateTimeStd)
}

And, voila! I can make a datePicker disappear without resorting to tableView!