对象层次结构导致Swift中的内存泄漏

问题描述

我已经能够提炼我在我编写的应用程序中看到的问题，并在一个简单的例子中复制了它。

鉴于这些类：

  class Thing {
 var name：String =
 var price：Double = 0.0 
 var更改：Double = 0.0 
 var percentChanged：Double = 0.0 
} 
 
 class TestUIViewController：UIViewController {
 
} 
 
 class ViewController：TestUIViewController {
 
 var thing：Thing？ 
 
 @IBAction func clicked（_ sender：AnyObject）{
 self.thing = Thing（）
} 
 
} 
  

我用按钮创建了一个UIView，当按下时，会实例化一个东西。使用Instruments分析器，我可以看到发生内存泄漏。

但是，如果ViewController类从UIViewController扩展，则没有问题。

这一切都是从一个快速测试应用程序转载而来的，因此我无法想到其他外部力量。

这里是示例代码 -

这是预期的结果。有9个瞬态东西，只有一个持久的东西 - 目前分配给该属性的东西。如果有多个持久性Thing就会出现泄漏，而且没有。

此外，这就是Xcode中内存规格的样子：

我们有点上升（一种台面 ）当我反复点击按钮时，我们再次回到基准水平。

Ive been able to distill a problem seen in an app I've written, and have reproduced it in a simple example.

Given these classes:

class Thing {
    var name:String = ""
    var price:Double = 0.0
    var changed:Double = 0.0
    var percentChanged:Double = 0.0
}

class TestUIViewController: UIViewController {

}

class ViewController: TestUIViewController {

    var thing:Thing?

    @IBAction func clicked(_ sender: AnyObject) {
        self.thing = Thing()
    }

}

I created a UIView with a button, that when pressed, a thing is instantiated. With the Instruments profiler up, I can see memory leaks occurring.

However, if the ViewController class extends from UIViewController, there are no issues.

This was all reproduced from a quick test app, so there are no other external forces at play here that i can think of.

Here is the example code - https://www.dropbox.com/s/ooqh77lhpzbvpv1/ArcTest.zip?dl=0

解决方案

You may have found a bug in the leak detector, and it could be quite an interesting bug, so you should report it to Apple. But there is in fact no leak. I downloaded and ran your project under Instruments and clicked the button 10 times. This is what I saw in Instruments allocations template:

That is the expected result. There are 9 transient Things, and only one persistent Thing — the one currently assigned to the property. A leak would be if there were more than one persistent Thing, and there isn't.

Also, this is what the memory gauge looks like in Xcode:

We get a little rise (a kind of "mesa") when I repeatedly tap the button, but then we settle back down to the base level again.

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