什么时候UIViewControllers解除分配？

Question

我很难弄清楚UIViewControllers何时应该解除分配。我创建了最简单的测试，其中我在故事板上有3个UIViewControllers，每个都有一个按钮，执行下一个segue，所以1-> 2-> 3-＆gt; 1-＆gt; ..等等向前。然后我记录了出现/消失加载和init / deinit方法，但是从未调用deinit。

日志如下所示：

<StoryBoardTest.TestViewController: VC1> init
<StoryBoardTest.TestViewController: VC1> View did load
<StoryBoardTest.TestViewController: VC1> View did appear
<StoryBoardTest.TestViewController: VC2> init
<StoryBoardTest.TestViewController: VC2> View did load
<StoryBoardTest.TestViewController: VC2> View did appear
<StoryBoardTest.TestViewController: VC1> View did disappear
<StoryBoardTest.TestViewController: VC3> init
<StoryBoardTest.TestViewController: VC3> View did load
<StoryBoardTest.TestViewController: VC3> View did appear
<StoryBoardTest.TestViewController: VC2> View did disappear
<StoryBoardTest.TestViewController: VC4> init
<StoryBoardTest.TestViewController: VC4> View did load
<StoryBoardTest.TestViewController: VC4> View did appear
<StoryBoardTest.TestViewController: VC3> View did disappear
<StoryBoardTest.TestViewController: VC5> init
<StoryBoardTest.TestViewController: VC5> View did load
<StoryBoardTest.TestViewController: VC5> View did appear
<StoryBoardTest.TestViewController: VC4> View did disappear
<StoryBoardTest.TestViewController: VC6> init
<StoryBoardTest.TestViewController: VC6> View did load
<StoryBoardTest.TestViewController: VC6> View did appear
<StoryBoardTest.TestViewController: VC5> View did disappear
<StoryBoardTest.TestViewController: VC7> init
<StoryBoardTest.TestViewController: VC7> View did load
<StoryBoardTest.TestViewController: VC7> View did appear
<StoryBoardTest.TestViewController: VC6> View did disappear

如果我将这些嵌入到NavigationController中，这看起来就像我期望的那样，但我不这样做。有人可以阐明为什么这不会消失吗？作为奖励，如果它在NavigationController中会有什么不同。

VC类：

import UIKit

class TestViewController: UIViewController {

    required init?(coder aDecoder: NSCoder) {
        super.init(coder: aDecoder)
        print("\(self.description) init")
    }

    deinit {
        print("\(self.description) deinit")
    }

    override func viewDidLoad() {
        super.viewDidLoad()
        print("\(self.description) View did load")
    }

    override func viewDidAppear(_ animated: Bool) {
        super.viewDidAppear(animated)
        print("\(self.description) View did appear")
    }

    override func viewDidDisappear(_ animated: Bool) {
        super.viewDidDisappear(animated)
        print("\(self.description) View did disappear")

    }

}

故事板看起来像这样：