APP进入后台后才会释放内存

Question

我正在开发一个带侧边菜单的应用程序，在ContainController中使用两个ViewController。当关闭侧面菜单ViewController（调用deinit方法）后，内存就不会被释放（大概是23 MiB），直到应用程序进入后台。在Xcode 9中构建的“Leaks”工具表示根本没有内存泄漏......任何人都可以告诉我什么是错的？非常感谢提前！

import UIKit
import CoreData

enum MenuState {
    case Collapsed 
    case Expanding  
    case Expanded 
}

class ContainerViewController: UIViewController {

    weak var managedObjectContext: NSManagedObjectContext!

    weak var mainViewController: MasterViewController!

    weak var menuViewController: MenuViewController?

    var currentState = MenuState.Collapsed {
        didSet {
            let shouldShowShadow = currentState != .Collapsed
            showShadowForMainViewController(shouldShowShadow: shouldShowShadow)
    }
}

override func viewDidLoad() {
    super.viewDidLoad()

    mainViewController = UIStoryboard(name: "Main", bundle: nil).instantiateViewController(withIdentifier: "mainView") as! MasterViewController
    view.addSubview(mainViewController.view)

    DispatchQueue.global(qos: .userInteractive).async {
        self.mainViewController.managedObjectContext = self.managedObjectContext
        self.addChildViewController(self.mainViewController)
        self.mainViewController.didMove(toParentViewController: self)
    }

    let panGestureRecognizer = UIPanGestureRecognizer(target: self, action:#selector(self.handlePanGesture(_:)))
    self.mainViewController.view.addGestureRecognizer(panGestureRecognizer)

    let tapGestureRecognizer = UITapGestureRecognizer(target: self, action:#selector(self.handleTapGesture))
    self.mainViewController.view.addGestureRecognizer(tapGestureRecognizer)
}


@objc func handlePanGesture(_ recognizer: UIPanGestureRecognizer) {

    switch(recognizer.state) {

    case .began:

        let dragFromLeftToRight = (recognizer.velocity(in: view).x > 0)
        if (currentState == .Collapsed && dragFromLeftToRight) {
            currentState = .Expanding
            addMenuViewController()
        }

    case .changed:

        let positionX = recognizer.view!.frame.origin.x + recognizer.translation(in: view).x
        recognizer.view!.frame.origin.x = positionX < 0 ? 0 : positionX

        let boundX = mainViewController.view.frame.width - menuViewExpandedOffset
        if positionX > 0 {
            recognizer.view!.frame.origin.x = positionX > boundX ? boundX : positionX
        }
        recognizer.setTranslation(.zero, in: view)

    case .ended:

        let boundX = mainViewController.view.frame.width - menuViewExpandedOffset
        let hasMovedhanHalfway = (recognizer.view!.frame.origin.x > boundX * 0.3)
        animateMainView(shouldExpand: hasMovedhanHalfway)

    default:
        break
    }
}

@objc func handleTapGesture() {
    if currentState == .Expanded {

        animateMainView(shouldExpand: false)
    }
}

//ADD MENUVC
func addMenuViewController() {
    if (menuViewController == nil) {
        menuViewController = UIStoryboard(name: "Main", bundle: nil)
            .instantiateViewController(withIdentifier: "menuView")
            as? MenuViewController

        view.insertSubview(menuViewController!.view, at: 0)

        addChildViewController(menuViewController!)
        menuViewController!.didMove(toParentViewController: self)
    }
}

let menuViewExpandedOffset: CGFloat = 480


func animateMainView(shouldExpand: Bool) {

    if (shouldExpand) {

        currentState = .Expanded
        animateMainViewXPosition(targetPosition: mainViewController.view.frame.width -
            menuViewExpandedOffset)
    }

    else {
        animateMainViewXPosition(targetPosition: 0) { finished in

            self.currentState = .Collapsed

            self.menuViewController?.view.removeFromSuperview()
            self.menuViewController?.removeFromParentViewController()
            self.menuViewController = nil
        }
    }
}



func animateMainViewXPosition(targetPosition: CGFloat,
                              completion: ((Bool) -> Void)! = nil) {

    UIView.animate(withDuration: 0.5, delay: 0, usingSpringWithDamping: 1.0,
                   initialSpringVelocity: 0, options: .curveEaseOut, animations: {
                    self.mainViewController.view.frame.origin.x = targetPosition
    }, completion: completion)
}

func showShadowForMainViewController(shouldShowShadow: Bool) {
    if (shouldShowShadow) {
        mainViewController.cameraBGimage.layer.shadowOpacity = 0.6
        mainViewController.cameraBGimage.layer.shadowOffset = CGSize(width: 0, height: 1)
    } else {
        mainViewController.cameraBGimage.layer.shadowOpacity = 0.0
    }
}


}