将数据传递回上一个视图控制器（实例成员不能在类型错误时使用）

问：

我有 2 个值，用于跟踪用户可以在应用内购买的权益类型的当前值。我想在purchaseViewController中更新它们，并在关闭purchaseViewController后在上一个视图控制器中使用它们。我尝试使用协议/委托和回调来执行此操作。但是，我得到的错误基本上相同，两者都说“实例成员'委托/回调'不能用于类型'purchasesViewController'”。这是我第一次尝试传回数据，我主要只是按照教程进行操作，并且可能在此过程中错过了一步，但我认为这两种方法都会出现相同类型的错误，这很奇怪。

父视图控制器上的代码：

func sendBack(staticIncreases: Int, percentIncreases: Int) { //Protocol function
    self.avalibleIncreases = staticIncreases
    self.currentPercentIncreases = percentIncreases
}

override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
    if segue.identifier ==  "improveFromOpen"{
        let next = segue.destination as! purchasesViewController
        next.currentPercentIncreases = currentPercentIncreases
        next.username = username
        next.avalibleIncreases = avalibleIncreases
        purchasesViewController.delegate = self //Error "Instance member 'delegate' cannot be used on type 'purchasesViewController'"
        purchasesViewController.callback = { result in //Error "Instance member 'delegate' cannot be used on type 'purchasesViewController'"
            self.avalibleIncreases = result[0]
            self.currentPercentIncreases = result[1]
        }
    }

purchaseViewController 上的代码：

protocol updateBoosts {
    func sendBack(staticIncreases: Int, percentIncreases: Int)
}

class purchasesViewController: UIViewController {

    var delegate: updateBoosts? = nil
    var callback : (([Int])->())?

    var username: String!
    var currentPercentIncreases: Int!
    var avalibleIncreases: Int!

func sendBackVals(){
    if self.delegate != nil {
        self.delegate?.sendBack(staticIncreases: avalibleIncreases, percentIncreases: currentPercentIncreases)
    }

    let out = [avalibleIncreases!, currentPercentIncreases] as [Int]
    callback?(out)
}

override func viewWillDisappear(_ animated: Bool) {
    sendBackVals()
}

知道我的错误在哪里吗？