錯誤：在self.init初始化self之前，在屬性訪問“ content”中使用“ self”

Question

我已經看到關鍵字Use of 'self' in property所有問題，但仍然無法解決。 我剛剛開始學習Swift 3.01，而我的Xcode版本是8.2。 請幫我！

我正在更改Apple提供的應用程序 。

我想創建一個textView以便用戶可以輸入文本並將其存儲。 當我更改Meal.swift ，出現錯誤： Error :Use of 'self' in property access 'content' before self.init initializes self在代碼末尾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
  }
}

請幫助我找到那里的問題，最好的問候！

Answer 1

您也必須解碼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)
}

順便說一句：在encode / decode方法中guard值會揭示開發人員/設計錯誤。 除了應用程序之外，沒有其他人可以創建這些對象，並且您應該知道該值確實存在。 你不能guard趕上這實際上應該不會發生運行時錯誤。

Answer 2

我已經解決了我的問題，在MealViewController的func prepare添加let content = content.text

看起來就像這樣：

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!)

}

只是給大家一個參考。 希望你會喜歡。