swift - Swift 中数据模型的动态属性(getters/setters)

Question

我正在尝试使用 Swift(我是新手)为我的数据模型创建一个干净的界面。这些模型由 Firebase 支持(尽管这最终与实际问题无关)。我想避免的是一遍又一遍地编写大量的 setter/accessor 样板代码。

例如:

class MyData {
  let connection: Firebase!

  private var _name: String? // internal storage, like an iVar in ObjC

  init(connection: Firebase!) {
    self.connection = connection
    self.connection.observeEventType(.Value, withBlock: { snapshot in
      _name = snapshot["name"]
    }
  }

  var name: {
    get {
      return _name
    }
    set(name) {
      // When the client sets the name, write it to Firebase
      _name = name
      self.connection.childByAppendingPath("name").setValue(name)
    }
  }
}

我确信我在那里犯了很多错误。这个想法是在实例化时首先从服务器加载数据。随后，我们可以调用 my_data_instance.name 来获取该名称，或者 my_data_instance.name = "foo" 并且该名称将自动写入服务器。

单个属性需要大约 10 行代码(其中会有很多)。疯了!一定有更好的方法!

---

编辑:明确地说，我想避免编写尽可能多的样板代码。考虑像 Mantle 这样的库，其中仅定义一个 @property 就足以做你想做的一切。在我看来，如果不止一行代码说 I have an attribute called "name", handle it via Firebase 就过于冗长了。

Answer 1

您可以使用 Key-Value Observing监控您的属性的变化。更多信息在 Adopting Cocoa Design Patterns in Swift .

import Foundation

private var KVOContext = 0

// Your class must inherit from NSObject
class MyData : NSObject {
    private let propertiesToObserve = ["name", "location"]

    dynamic var name: String
    dynamic var location: String

    init(name: String, location: String) {
        self.name = name
        self.location = location
        super.init()

        // Add the properties that you want to observe
        for property in self.propertiesToObserve {
            self.addObserver(self, forKeyPath: property, options: [.New, .Old], context: &KVOContext)
        }
    }

    // This method is called whenever an observed property is changed
    override func observeValueForKeyPath(keyPath: String?, ofObject object: AnyObject?, change: [String : AnyObject]?, context: UnsafeMutablePointer<Void>) {
        if let property = keyPath,
            newValue = change![NSKeyValueChangeNewKey],
            oldValue = change![NSKeyValueChangeOldKey] {
                print("\(property) changed from \(oldValue) to \(newValue)")
                // If oldValue != newValue, write back to Firebase
        }
    }

    // Remove self as observer of self
    deinit {
        for property in self.propertiesToObserve {
            self.removeObserver(self, forKeyPath: property)
        }
    }
}

let data = MyData(name: "John", location: "Chicago")
data.name = "David"         // print: name changed from John to David
data.location = "New York"  // print: location changed from Chicago to New York