UITextField inputView with UIDatePicker. Opens a datepicker view with a done button

datepickerexample.swift

// Make a view with date picker and done button
func makeDatePickerWithDoneButton() {
    let inputView = UIView(frame: CGRectMake(0,0, self.view.frame.width, 240))
    
    var datePicker = UIDatePicker(frame: CGRect(x: 0, y: 40, width: 0, height: 0))
    datePicker.datePickerMode = .Date
    inputView.addSubview(datePicker)
    datePicker.addTarget(self, action: Selector("handleDatePicker:"), forControlEvents: .ValueChanged)
    
    let doneButton = UIButton(frame: CGRect(x: (self.view.frame.size.width/2) - (100/2), y: 0, width: 100, height: 50))
    doneButton.setTitle("Done", forState: .Normal)
    inputView.addSubview(doneButton)
    doneButton.addTarget(self, action: Selector("handleDoneButton:"), forControlEvents: .TouchUpInside)
    
    handleDatePicker(datePicker)
    
    textField.inputView = inputView
}

func handleDatePicker(sender: UIDatePicker) {
    let formatter = NSDateFormatter()
    formatter.dateFormat = "yyyy-MM-dd"
    textField.text = formatter.stringFromDate(sender.date)
}

func handleDoneButton(sender: UIButton) {
    textField.resignFirstResponder()
}


func datePickerValueChanged(sender: UIDatePicker) {
    let formatter = NSDateFormatter()
    formatter.dateStyle = NSDateFormatterStyle.MediumStyle
    textField.text = formatter.stringFromDate(sender.date)
}

Update to swift5:

// Make a view with date picker and done button
    func makeDatePickerWithDoneButton() {
        let inputView = UIView(frame: CGRectMake(0,0, self.view.frame.width, 240))
        
        var datePicker = UIDatePicker(frame: CGRect(x: 0, y: 40, width: 0, height: 0))
        datePicker.datePickerMode = .date
        inputView.addSubview(datePicker)
        datePicker.addTarget(self, action: #selector(handleDatePicker(sender:)), for: .valueChanged)
        
        let doneButton = UIButton(frame: CGRect(x: (self.view.frame.size.width/2) - (100/2), y: 0, width: 100, height: 50))
        doneButton.setTitle("Hecho", forState: .Normal)
        inputView.addSubview(doneButton)
        doneButton.addTarget(self, action: #selector(handleDoneButton(sender:)), forControlEvents: .touchUpInside)
        
        handleDatePicker(sender: datePicker)
        
        textField.inputView = inputView
    }

    @objc func handleDatePicker(sender: UIDatePicker) {
        let formatter = DateFormatter()
        formatter.dateFormat = "yyyy-MM-dd"
        textField.text = formatter.stringFromDate(sender.date)
    }

    @objc func handleDoneButton(sender: UIButton) {
        textField.resignFirstResponder()
    }


    func datePickerValueChanged(sender: UIDatePicker) {
        let formatter = DateFormatter()
        formatter.dateStyle = .medium
        textField.text = formatter.stringFromDate(sender.date)
    }