How to convert AnyClass to a specific Class and init it dynamically in Swift?

Question

In Object-C I store Class objects in an array and init them dynamically like this:

self.controllers=@[[OneViewController class],[TwoViewController class]];
Class clz = self.controllers[index];
UIViewController *detailViewController = [[clz alloc] init];

In Swift i try this way but it raises an error:

var controllers:AnyClass[] = [OneViewController.self,TwoViewController.self]
var clz : AnyClass = controllers[index]
var instance = clz() // Error:'AnyObject' is not constructible with ()

I wonder Whether there is a way to convert AnyClass to a specific Class? Or any other good ideas?

score 56 · Accepted Answer · edited Sep 21 '17 at 19:03

56

You can specify the array to be of the common superclass' type, then type deduction does the right thing (Beta-3 syntax):

let classArray: [UIViewController.Type] = [
    OneViewController.self, TwoViewController.self
]
let controllerClass = classArray[index]
let controller = controllerClass.init()

edited Sep 21 '17 at 19:03

iwasrobbed

46,496
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answered Jul 12 '14 at 21:34

DarkDust

90,870
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5

"Initializing from a metatype value must reference 'init' explicitly", so `controllerClass.init()` it is now. – ctietze Dec 19 '15 at 10:50

Xianng · Answer 2 · 2014-07-09T02:46:56.057

12

i have found a way to solve this problem:

var controllers:AnyClass[] = [OneViewController.self,TwoViewController.self]
var clz: NSObject.Type = controllers[0] as NSObject.Type
var con = clz()

remember to add @objc in the class of ViewController

edited Jul 09 '14 at 02:46

answered Jul 04 '14 at 07:26

Xianng

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14

I needed the `as NSObject.Type` – abc123 Nov 27 '20 at 19:35

Maic López Sáenz · Answer 3 · 2015-11-25T19:54:16.207

An AnyClass variable must first be casted into a specific type in order to initialize an instance:

// Code checked to run on xCode 7.1.1
import UIKit

var aClass: AnyClass = UIButton.self

// Error: 'init' is a member of the type...
// let doesNotWork = aClass.init()

// aClass must be casted first
var buttonClass = aClass as! UIButton.Type
var oneButton = buttonClass!.init()
var otherButton = buttonClass!.init(frame: CGRectZero)

Sentry.co · Answer 4 · 2022-06-24T19:37:39.037

8

Here is a pure swift implementation of dynamic class types. It does require the classes to extend the same protocol.

protocol ILayout { init(_ a:S tring) }   
class A: ILayout { required init(_ a: String) }  
class B: ILayout { required init(_ a:String) }   
var instance: ILayout   
var classType: ILayout.Type

classType = A.self   
instance = classType.init("abc")

classType = B.self   
instance = classType.init("abc")

edited Jun 24 '22 at 19:37

answered Nov 12 '15 at 05:56

Sentry.co

5,355
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@bazyl87 Thanks for the edit. I totally agree that your edit is more readable in code. But this isn't production code , it's just meant as a quick way to glean a methodology, where compactness is preferred. IMO – Sentry.co Oct 04 '18 at 10:18

score 0 · Answer 5 · answered Jun 10 '14 at 05:08

If the classes are all Objective-C NSObject subclasses, you can do something like this (yes, the backticks are intentional):

var constructors: (Void -> NSObject!)[] = [ NSMutableString.`new`, NSMutableArray.`new`, NSMutableDictionary.`new` ]

let string = constructors[0]()
(string as NSMutableString).appendString("Hello")

let array = constructors[1]()
(array as NSMutableArray).addObject("Swift")

let dictionary = constructors[2]()
(dictionary as NSMutableDictionary).setObject("Objective-C", forKey: "Goodbye")

NSLog("dynamically created a string: \(string), an array: \(array), and a dictionary: \(dictionary)")

It should output:

dynamically created a string: Hello, an array: (
    Swift
), and a dictionary: {
    Goodbye = "Objective-C";
}

It does seem to me that there should be a more elegant way to do this.

How to convert AnyClass to a specific Class and init it dynamically in Swift?

5 Answers5

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