错误：在 self.init 初始化 self 之前，在属性访问“内容”中使用“自我”

Question

我已经看到了关键字Use of 'self' in property 的所有问题 但仍然无法解决。我刚开始学习 swift 3.01，我的 Xcode 版本是 8.2。请帮帮我！

我正在更改the app Apple provided。

我想创建一个textView，以便用户可以键入文本并存储它。 当我更改Meal.swift 时，出现错误： Error :Use of 'self' in property access 'content' before self.init initializes self 就在代码的最后：

import UIKit
import os.log

class Meal: NSObject, NSCoding {

  //MARK: Properties
  var name: String
  var photo: UIImage?
  var content: String    

  //MARK: Archiving Paths
  static let DocumentsDirectory = FileManager().urls(for: .documentDirectory, in: .userDomainMask).first!
  static let ArchiveURL = DocumentsDirectory.appendingPathComponent("meals")

  //MARK: Types
  struct PropertyKey {
    static let name = "name"
    static let photo = "photo"
    static let content = "content"
  }

  //MARK: Initialization
  init?(name: String, photo: UIImage?, content: String) {
    // The name must not be empty
    guard !name.isEmpty else {
      return nil
    }

    // The content must not be empty
    guard !content.isEmpty else {
      return nil
    }

    // Initialize stored properties.
    self.name = name
    self.photo = photo
    self.content = content
  }

  //MARK: NSCoding
  func encode(with aCoder: NSCoder) {
    aCoder.encode(name, forKey: PropertyKey.name)
    aCoder.encode(photo, forKey: PropertyKey.photo)
    aCoder.encode(content, forKey: PropertyKey.content) 
  }

  required convenience init?(coder aDecoder: NSCoder) {
    // The name is required. If we cannot decode a name string, the initializer should fail.
    guard let name = aDecoder.decodeObject(forKey: PropertyKey.name) as? String else {
      os_log("Unable to decode the name for a Meal object.", log: OSLog.default, type: .debug)
      return nil
    }

    // Because photo is an optional property of Meal, just use conditional cast.
    let photo = aDecoder.decodeObject(forKey: PropertyKey.photo) as? UIImage

    // Must call designated initializer.
    self.init(name: name, photo: photo, content: content)// Error happened to here by this : Error :Use of 'self' in property access 'content' before self.init initializes self
  }
}

请帮我找出问题所在，最好的祝福！

Answer 1

你也必须解码content

required convenience init?(coder aDecoder: NSCoder) {

    // The name is required. If we cannot decode a name string, the initializer should fail.
    let name = aDecoder.decodeObject(forKey: PropertyKey.name) as! String

    // Because photo is an optional property of Meal, just use conditional cast.
    let photo = aDecoder.decodeObject(forKey: PropertyKey.photo) as? UIImage

    let content = aDecoder.decodeObject(forKey: PropertyKey.content) as! String
    // Must call designated initializer.        
    self.init(name: name, photo: photo, content: content)
}

顺便说一句：encode/decode 方法中的guarding 值揭示了开发人员/设计错误。除了应用程序之外没有其他人可以创建这些对象，并且您应该知道该值确实存在。你不能guard 来捕捉实际上永远不会发生的运行时错误。

Answer 2

我已经解决了我的问题，在MealViewController 的func prepare 中添加let content = content.text

完全是这样的：

override func prepare(for segue: UIStoryboardSegue, sender: Any?) {

    super.prepare(for: segue, sender: sender)

    // Configure the destination view controller only when the save button is pressed.
    guard let button = sender as? UIBarButtonItem, button === saveButton else {
        os_log("The save button was not pressed, cancelling", log: OSLog.default, type: .debug)
        return
    }

    let name = nameTextField.text ?? ""
    let photo = photoImageView.image
    let content = content.text // Add this new code.

    // Set the meal to be passed to MealTableViewController after the unwind segue.
    meal = Meal(name: name, photo: photo, content: content!)

}

只是给大家做个参考。希望你会喜欢。