DidSet not working in init function swift 3

Question

I have already seen

Is it possible to allow didSet to be called during initialization in Swift?

for me it is not working..

I am working in project where I have created class below

protocol FileManagerHelper {

    var fileName:String {get}
    var fileCategory:FileCategory {get set}
    var isFileExitsAtPath:Bool {get}
    var filePath:String {get}
    var fileType:FileTypes {get set}

}

class FileManager:FileManagerHelper {
    // Other property 

    //STORED PROPERY INIT WHEN OBJECT WILL CREATED WITH FileCategory OBJECT 
     var fileCategory:FileCategory  {
    didSet {
        switch fileCategory {
        case .XYZ:
            print("Test")


        ... other cases 
         }
     }

    required init(fileCategory:FileCategory,fileType:FileTypes = .Image) {

        self.fileCategory = fileCategory
        self.path = self.folderPath + self.fileName

   }

 }

did set method is not calling of fileCategory

NOTE: I don't want to give default value , I want to pass it runtime from init method

Tries

1) defer

use of self in method called $defer before all stored property are initialised

2) Create custom method that will assign that value and call it from init

 private func setCategory(with category:FileCategory) {
    self.fileCategory = category
}

Use of method call setCategory before stored property ...

I know that all stored property should be initialised before instance created. Till that instance will not been created so i won't call methods (using self) may be that why above solution not working

Please help me if any one have idea

according to apple documents -: The willSet and didSet observers of superclass properties are called when a property is set in a subclass initializer, after the superclass initializer has been called. They are not called while a class is setting its own properties, before the superclass initializer has been called. — Tushar Sharma, Nov 02 '17 at 10:31
@TusharSharma Agree !! Thanks for your efforts but please check link i have added where the property is calling didSet with defer keyword so it looks like possible to initialise in property (with didSet) in self within in the init method — Prashant Tukadiya, Nov 02 '17 at 10:35

score 5 · Accepted Answer · answered Nov 02 '17 at 10:48

5

For me, using the defer is better readable.

import Foundation

class A {
    var b: String {
        didSet {
            print("didSet called with value: \(b)")
        }
    }

    init(x: String) {
        self.b = x
        defer { self.b = x }
    }
}

let a = A(x: "It's Working!") // didSet called with value: It's Working!
print(a.b) // It's Working

answered Nov 02 '17 at 10:48

Štefan Ľupták

126
1
6

Why Two times self.b = x ? – Prashant Tukadiya Nov 02 '17 at 11:58
2

First time to satisfy the compiler, second time to call the `didSet`. – Štefan Ľupták Nov 02 '17 at 12:50

score 0 · Answer 2 · answered Nov 02 '17 at 10:38

One way to solve this is to extract the didSet logic into a separate method and call this method from both didSet and init:

class FileManager: FileManagerHelper {

  var fileCategory:FileCategory  {
    didSet {
      didSetFileCategory()
    }
  }

  required init(fileCategory:FileCategory,fileType:FileTypes = .Image) {
    self.fileCategory = fileCategory
    self.path = self.folderPath + self.fileName
    didSetFileCategory()
  }

  private func didSetFileCategory() {
    switch fileCategory {
    case .XYZ:
      print("Test")
    //... other cases 
    }
  }
}

DidSet not working in init function swift 3

2 Answers2

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