【Swift】PresentedViewControllerからRootViewControllerを変更するとメモリリークする件

2019年9月21日

モーダルのようにPresentしたViewControllerからRootViewControllerを変更した際に、メモリリークしていたのでリークしない方法を調べました。

1. 問題の再現

1-1. 構成

構成図は以下のようになっています。

PresentingViewController（最初のRootViewController）
PresentedViewController（モーダルのようにPresentされるViewController）
TopViewController（変更先のRootViewController）

1-2. 流れ

流れは以下です。

それぞれのコードは以下です。

import Foundation
import UIKit

class PresentingViewController: UIViewController {
    
    override func viewDidLoad() {
        super.viewDidLoad()
    }
    
    
    @IBAction func presentViewController(_ sender: Any) {
        let storyboard = UIStoryboard(name: "Main", bundle: nil)
        let presentedVC = storyboard.instantiateViewController(withIdentifier: "PresentedViewController") as! PresentedViewController
        self.present(presentedVC, animated: true, completion: nil)
    }
    
}

import Foundation

import UIKit

class PresentingViewController: UIViewController {

override func viewDidLoad() {

super.viewDidLoad()

}

@IBAction func presentViewController(_ sender: Any) {

let storyboard = UIStoryboard(name: "Main", bundle: nil)

let presentedVC = storyboard.instantiateViewController(withIdentifier: "PresentedViewController") as! PresentedViewController

self.present(presentedVC, animated: true, completion: nil)

}

import Foundation
import UIKit

class PresentedViewController: UIViewController {
    
    override func viewDidLoad() {
        super.viewDidLoad()
    }
    
    @IBAction func changeRootViewController(_ sender: Any) {
        appDelegate.changeRootViewController()
        self.dismiss(animated: true, completion: nil)
    }
    
}

import Foundation

import UIKit

class PresentedViewController: UIViewController {

override func viewDidLoad() {

super.viewDidLoad()

}

@IBAction func changeRootViewController(_ sender: Any) {

appDelegate.changeRootViewController()

self.dismiss(animated: true, completion: nil)

}

import Foundation
import UIKit

class TopViewController: UIViewController {
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        
    }
    
}

import Foundation

import UIKit

class TopViewController: UIViewController {

override func viewDidLoad() {

super.viewDidLoad()

}

import UIKit

let appDelegate:AppDelegate = UIApplication.shared.delegate as! AppDelegate

@UIApplicationMain
class AppDelegate: UIResponder, UIApplicationDelegate {

    var window: UIWindow?

    func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?) -> Bool {
        // Override point for customization after application launch.
        return true
    }

    func applicationWillResignActive(_ application: UIApplication) {
        // Sent when the application is about to move from active to inactive state. This can occur for certain types of temporary interruptions (such as an incoming phone call or SMS message) or when the user quits the application and it begins the transition to the background state.
        // Use this method to pause ongoing tasks, disable timers, and invalidate graphics rendering callbacks. Games should use this method to pause the game.
    }

    func applicationDidEnterBackground(_ application: UIApplication) {
        // Use this method to release shared resources, save user data, invalidate timers, and store enough application state information to restore your application to its current state in case it is terminated later.
        // If your application supports background execution, this method is called instead of applicationWillTerminate: when the user quits.
    }

    func applicationWillEnterForeground(_ application: UIApplication) {
        // Called as part of the transition from the background to the active state; here you can undo many of the changes made on entering the background.
    }

    func applicationDidBecomeActive(_ application: UIApplication) {
        // Restart any tasks that were paused (or not yet started) while the application was inactive. If the application was previously in the background, optionally refresh the user interface.
    }

    func applicationWillTerminate(_ application: UIApplication) {
        // Called when the application is about to terminate. Save data if appropriate. See also applicationDidEnterBackground:.
    }


}

extension AppDelegate {

    func changeRootViewController(){
        if let window = window {
            let storyboard = UIStoryboard(name: "Main", bundle: nil)
            let topVC = storyboard.instantiateViewController(withIdentifier: "TopViewController") as! TopViewController

            UIView.transition(with: window,
                              duration: 0.3,
                              options: .transitionCrossDissolve,
                              animations: {
                                window.rootViewController = topVC
            }, completion: nil)

        }
    }
}

import UIKit

let appDelegate:AppDelegate = UIApplication.shared.delegate as! AppDelegate

@UIApplicationMain

class AppDelegate: UIResponder, UIApplicationDelegate {

var window: UIWindow?

func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?) -> Bool {

// Override point for customization after application launch.

return true

}

func applicationWillResignActive(_ application: UIApplication) {

// Sent when the application is about to move from active to inactive state. This can occur for certain types of temporary interruptions (such as an incoming phone call or SMS message) or when the user quits the application and it begins the transition to the background state.

// Use this method to pause ongoing tasks, disable timers, and invalidate graphics rendering callbacks. Games should use this method to pause the game.

}

func applicationDidEnterBackground(_ application: UIApplication) {

// Use this method to release shared resources, save user data, invalidate timers, and store enough application state information to restore your application to its current state in case it is terminated later.

// If your application supports background execution, this method is called instead of applicationWillTerminate: when the user quits.

}

func applicationWillEnterForeground(_ application: UIApplication) {

// Called as part of the transition from the background to the active state; here you can undo many of the changes made on entering the background.

}

func applicationDidBecomeActive(_ application: UIApplication) {

// Restart any tasks that were paused (or not yet started) while the application was inactive. If the application was previously in the background, optionally refresh the user interface.

}

func applicationWillTerminate(_ application: UIApplication) {

// Called when the application is about to terminate. Save data if appropriate. See also applicationDidEnterBackground:.

}

extension AppDelegate {

func changeRootViewController(){

if let window = window {

let storyboard = UIStoryboard(name: "Main", bundle: nil)

let topVC = storyboard.instantiateViewController(withIdentifier: "TopViewController") as! TopViewController

UIView.transition(with: window,

duration: 0.3,

options: .transitionCrossDissolve,

animations: {

window.rootViewController = topVC

}, completion: nil)

}

アプリがクラッシュする訳ではないので、一見問題ないように見えますが、Debug View Hierarchyを見てみましょう。

RootViewControllerをTopViewControllerに変更してもなお裏にUITransitionViewが残っており、中にはPresentedViewControllerが入っています。

このUITransitionViewは明示的に取り除かない限り、ずっと残り続けるので常にメモリリークしている状態になります。

原因となる部分は調べても見つかりませんでした；；

RootViewControllerを変更する際に内部でUIWindowを強参照してるんでしょうか？

2. UIWindowを変更する

RootViewControllerのみを変更するとメモリリークしてしまうので、UIWindowごと取り替えてしまいます。

UIWindowのsubviewを全て取り除く方法もありますが、あまり良くないらしいので上記の方法にしました。

AppDelegateのchangeRootViewController()を以下のように変更します。

func changeRootViewController(){
    if let window = window {
        let storyboard = UIStoryboard(name: "Main", bundle: nil)
        let topVC = storyboard.instantiateViewController(withIdentifier: "TopViewController") as! TopViewController

        let newWindow = UIWindow(frame: UIScreen.main.bounds)
        newWindow.rootViewController = topVC

        UIView.transition(with: window,
                          duration: 0.3,
                          options: .transitionCrossDissolve,
                          animations: {
                            self.window = nil
                            self.window = newWindow
                            self.window?.makeKeyAndVisible()
        }, completion:nil)
    }
}