inputview ios swift uibutton

How do I activate an inputView using a UIButton in Swift?

I am attempting to have a UIDatePicker come up as a keyboard when the user hits a UIButton. I was able to get it to work with a textfield, but I don’t like how the cursor is visible and the user could enter in any text if they had an external keyboard. Here is my code:

@IBAction func dateFieldStart(sender: UITextField) {
var datePickerStartView : UIDatePicker = UIDatePicker()
datePickerStartView.datePickerMode = UIDatePickerMode.Time
sender.inputView = datePickerStartView // error when sender is UIButton

I tried changing the sender to UIButton but it gave this error on the line that is marked above:

Cannot assign to 'inputView' in 'sender'

I have tried researching it and no one else seems to have had a problem with it. Anyone know how to trigger a UIDatePicker inputView using a UIButton or anything that might work better that the user cannot type into? Thanks!