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

Question

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

我正在更改Apple提供的应用程序 。

我想创建一个textView以便用户可以输入文本并将其存储。 当我更改Meal.swift ，出现错误： Error :Use of 'self' in property access 'content' before self.init initializes self在代码末尾Error :Use of 'self' in property access 'content' before self.init initializes self ：

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
  }
}

请帮助我找到那里的问题，最好的问候！

Answer 1

您也必须解码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：在encode / decode方法中guard值会揭示开发人员/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赶上这实际上应该不会发生运行时错误。

Answer 2

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

看起来就像这样：

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!)

}

只是给大家一个参考。 希望你会喜欢。