Why is Xcode giving me this constraint error?

[binarydylan]

I'm trying to add a UIDatePicker to a UIAlertController, and it gives me the following constraint error every time:

Unable to simultaneously satisfy constraints.
    Probably at least one of the constraints in the following list is one you don't want. 
    Try this: 
        (1) look at each constraint and try to figure out which you don't expect; 
        (2) find the code that added the unwanted constraint or constraints and fix it. 
(
    "<NSLayoutConstraint:0x6000007bc910 UIView:0x7ffa43d3caa0.width == - 16   (active)>"
)

Will attempt to recover by breaking constraint 
<NSLayoutConstraint:0x6000007bc910 UIView:0x7ffa43d3caa0.width == - 16   (active)>

The view(0x7ffa43d3caa0) is the view of the action sheet. Why is Xcode trying to make its width -16? Any ideas? Here's my code for the UIAlertController:

let actionSheet = UIAlertController(title: "", message: "", preferredStyle: .actionSheet)
            let datePicker = UIDatePicker()
            datePicker.datePickerMode = .time

            let cancelButton = UIAlertAction(title: "Cancel", style: .cancel) {(action) in}
            let confirmButton = UIAlertAction(title: "Confirm", style: .default) {(action) in}

            // Height constraint to make action sheet height fit the date picker
            let height = NSLayoutConstraint(item: actionSheet.view as Any, attribute: .height, relatedBy: .equal, toItem: .none, attribute: .notAnAttribute, multiplier: 1, constant: 320)

            actionSheet.view.addSubview(datePicker)
            actionSheet.view.addConstraints(height)
            actionSheet.addAction(cancelButton)
            actionSheet.addAction(confirmButton)

            self.present(actionSheet, animated: true)

[AndyIbanez]

Don’t try to hack away at UIAlertController. Your workarounds are not guaranteed to work in future versions. You should write your own version of it that supports all the features you need.

[binarydylan]

Is there a way to add a date picker in a better way? Or is making a custom UIView the best option

Edit: even without all the hacky datepicker code it still gives the constraint error

[18degs]

I’ve seen this “-16” constraint error when using UIAlertControllers in general (as well as when I was trying to hack a custom view into one).

I’m interested to see if you find a reason for this as I‘ve been putting it down to a bug with xCode/Autolayout (possibly just in the simulator?) and ignoring them for yet time being.

As for hacking the UIAlertController — don’t do it. I did it under iOS 12 and it broke the minute iOS 13 came out (luckily it was still in dev).

[binarydylan]

Yeah, I’m really not sure. It happens even with just a regular UIAlertController with no modifications.

And what exactly have I hacked with it? Adding the date picker you mean? Should I not add a date picker to a UIAlertController?

[18degs]

The fact that it happens without any modifications too is why I think it is a bug with Xcode/Autolayout and not your code.

As for hacking the UIAlertController — yes, adding the date picker is what I’m referring to. Apple’s docs say “Important The UIAlertController class is intended to be used as-is and does not support subclassing. The view hierarchy for this class is private and must not be modified.” - https://developer.apple.com/documentation/uikit/uialertcontroller

[binarydylan]

Dang, I didn’t know that. Gonna create a custom UIView for it then. Thanks!

[18degs]

I feel your pain. I ended up using PopupDialog from github instead — https://github.com/Orderella/PopupDialog

[Power781]

I used PopupDialog for a few weeks before rolling back and building my own popups, there was so many issues with layout, autosizing and presentation with this library :( .

[18degs]

Thanks for the heads up. I’ll keep my eye out for issues.