質問したいこと

datepickerで設定した日付と今日の日付の差を計算して、labelに
”あと○日”というのを表示させたいです。

コード

import UIKit

class testsViewController: UIViewController, UITextFieldDelegate {

    @IBOutlet weak var testdateField: UITextField!
@IBOutlet weak var testdatelabel: UILabel!

    func getToday(format:String = "dd") -> String {
        let now = Date()
        let formatter = DateFormatter()
        formatter.dateFormat = format
        return formatter.string(from: now as Date)
    }

    var saveData: UserDefaults = UserDefaults.standard
    var testdatePicker: UIDatePicker = UIDatePicker()
    var testdatePicker2: UIDatePicker = UIDatePicker()

    @objc func done_timer() {
        testdateField.endEditing(true)

        let formtter = DateFormatter()

        formtter.dateFormat = "yyyy年MM月dd日"

        testdateField.text = "\(formtter.string(from: testdatePicker.date))"
    }

    override func viewDidLoad() {
        super.viewDidLoad()

        testdatePicker.datePickerMode = UIDatePicker.Mode.date
        testdatePicker.timeZone = NSTimeZone.local
        testdatePicker.locale = Locale.current
        testdateField.inputView = testdatePicker

        testdatePicker2.datePickerMode = UIDatePicker.Mode.date
        testdatePicker2.timeZone = NSTimeZone.local
        testdatePicker2.locale = Locale.current


        testdateField.text = saveData.object(forKey: "testdate") as? String
// 決定バーの生成
        let toolbar_date = UIToolbar(frame: CGRect(x: 0, y: 0, width: view.frame.size.width, height: 35))
        let spacelItem = UIBarButtonItem(barButtonSystemItem: .flexibleSpace, target: self, action: nil)
        let doneItem = UIBarButtonItem(barButtonSystemItem: .done, target: self, action: #selector(done))
        toolbar_date.setItems([spacelItem, doneItem], animated: true)



        testdateField.inputView = testdatePicker
        testdateField.inputAccessoryView = toolbar_date



        testdateField.delegate = self
}
@objc func done() {
        testdateField.endEditing(true)

        let formatter = DateFormatter()

        formatter.dateFormat = "yyyy年MM月dd日"

        testdateField.text = "\(formatter.string(from: testdatePicker.date))"
    }
}

やってみたこと

とりあえず、今日の日付を取得するために

func getToday(format:String = "dd") -> String {
        let now = Date()
        let formatter = DateFormatter()
        formatter.dateFormat = format
        return formatter.string(from: now as Date)
    }

としてみましたが、その先どうすれば良いのか分からず…
よろしくお願いします。