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

Question

I've seen all the problems with keyword Use of 'self' in property but still couldn't solve it. I just started learning swift 3.01 and my Xcode version is 8.2. Please help me!

I was changing the app Apple provided .

I want to create a textView so users can type text and store it. While I was changing the Meal.swift , I got the error: Error :Use of 'self' in property access 'content' before self.init initializes self just at the end of the code:

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
  }
}

Please help me to find up the what's wrong in there, Best regard!

Answer 1

You have to decode content , too

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)
}

By the way: guard ing values in encode / decode methods reveals developer / design errors. Nobody else but the application can create those objects and you are supposed to know that the value does exist. You must not guard to catch runtime errors which should actually never occur.

Answer 2

I've solved my problem add let content = content.text in MealViewController 's func prepare

It's totally looks like that :

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!)

}

Just give everyone to be a referance. Hope you will enjoy.