title: Swift 4 UIDatePicker position to the bottom
body: <p>I have using <code>UIDatePicker</code>, I am wondering whats the best way to get in the same position as <code>UIPickerView</code> (the <code>UIPickerView</code> is always at the bottom) my <code>UIDatePicker</code> position if full width, but not at the bottom, if I remove the frame setting, it goes to the top left, not full width:</p>
  
  <pre><code>let datePicker: UIDatePicker = UIDatePicker()
  datePicker.datePickerMode = .date
  datePicker.frame = CGRect(x: 0, y: 50, width: self.view.frame.width, height: 200)
  datePicker.timeZone = NSTimeZone.local
  datePicker.backgroundColor = UIColor.white
  datePicker.addTarget(self, action: #selector(GradingController.datePickerValueChanged(_:)), for: .valueChanged)
  self.view.addSubview(datePicker)
  </code></pre>