UIDatePicker input view misaligns

I inherited an iOS project written in Swift 4.2, that uses a UIDatePicker as the input view of a text field:

Code Block swift
let datePicker = UIDatePicker()
datePicker.maximumDate = Date()
datePicker.datePickerMode = .date
datePicker.date = self.someDate
someTextField.inputView = datePicker
datePicker.addTarget(self, action: #selector(handleDatePicker(sender:)), for: .valueChanged)

^ The code snippet above is slightly obfuscated, but shows the basic logic.

The resulting input view is bottom-left aligned to the screen, with the majority of its bottom off-screen. (Sorry I can only describe it because I can't find a image host whose links are allowed on these forums.)

I've tried to manually align the input view by setting auto layout constraints:

Code Block swift
let datePicker = UIDatePicker()
datePicker.maximumDate = Date()
datePicker.datePickerMode = .date
datePicker.date = self.someDate
datePicker.translatesAutoresizingMaskIntoConstraints = false
datePicker.bottomAnchor.constraint(equalTo: self.view.bottomAnchor).isActive = true
datePicker.leadingAnchor.constraint(equalTo: self.view.leadingAnchor).isActive = true
datePicker.widthAnchor.constraint(equalTo: self.view.widthAnchor).isActive = true
someTextField.inputView = datePicker
datePicker.addTarget(self, action: #selector(handleDatePicker(sender:)), for: .valueChanged)

However, this only results in the program crashing.

What should I do to make the input view align properly on the screen?