将数据传回以前的视图控制器（实例成员不能用于类型错误）

Question

我有 2 个值来跟踪我的用户可以在应用程序中购买的各种福利的当前值。我想在 purchaseViewController 中更新它们，并在 purchaseViewController 被关闭后在以前的视图控制器中使用它们。我尝试用 protocol/delegate 和回调来做到这一点。但是，我得到的错误基本相同，都说 "Instance member 'delegate/callback' cannot be used on type '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，可能错过了其中的一步，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？

Answer 1

您的代码存在一些设计问题。

您应该同时使用 delegate 或 closure，因为两者的用途相同。否则，同样的事情会被执行两次。

如果您使用委托，则必须按如下所述对您的协议进行更改。此外，您还必须确认协议。

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
        next.delegate = self 
    }
}

确认协议

假设您要获取回调的当前视图控制器是 HomeViewController

// Confirming the protocol
extension HomeViewController: UpdateBoostsDelegate {
   func sendBack(staticIncreases: Int, percentIncreases: Int) {
    // write code here for handling the callback
   }
}

如果您想使用闭包，请移除委托。

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
        next.callback = { result in
                self.avalibleIncreases = result[0]
                self.currentPercentIncreases = result[1]
       }
    }

// Would be good if you add the semantic to protocol name
protocol UpdateBoostsDelegate: class {
    func sendBack(staticIncreases: Int, percentIncreases: Int)
}

PurchaseViewController

中的一些更正

class purchasesViewController: UIViewController {
// Make it weak so that no retain cycle is formed
   weak var delegate: UpdateBoostsDelegate?
// rest code will follow ....

建议

对于类、struct、enum、protocol，每个单词的第一个字符应该总是大写。
协议应该有语义，即如果创建它是为了通知事件，则添加 Delegate 后缀，或者如果创建它是为了满足数据需求，则添加 数据源协议名称中的后缀。

More about closure

Delegation design pattern

将数据传回以前的视图控制器（实例成员不能用于类型错误）

Passing data back to previous view controller (Instance member cannot be used on type error)

delegates

callback

uiviewcontroller

ios

swift

确认协议