如何在块外的 swift 中创建指向自身的弱指针

Question

我想在 swift 中创建一个指向自身的弱指针，就像我们以前在 objective-c 中那样

 __weak Something *weakself = self;

我发现有人在解释如何在块中使用 'weak self'，

    { in [unowned self] ...}

但我不想在我的块内定义 'weakself'，我想在块外定义 weakself

Answer 1

只需用weak关键字定义弱引用即可：

weak var weakSelf = self

来自documentation：

You indicate a weak reference by placing the weak keyword before a property or variable declaration.
...
NOTE: Weak references must be declared as variables, to indicate that their value can change at runtime. A weak reference cannot be declared as a constant.

Answer 2

在我看来你就像在 Objective-C 中那样试图避免使用块的保留循环，你创建了一个弱版本而不是引用自身：

__weak MyType *weakSelf = self;

void (^aBlock)() = ^void()
{
   [weakSelf doStuff];
}

这不是 Swift 处理此问题的方式。

相反，它具有捕获列表的概念，它告诉编译器引用块捕获的内容，以及如何处理它。您应该在 Swift 编程参考书中搜索 "Capture List" 并阅读该主题。引用本书：

“If you assign a closure to a property of a class instance, and the closure captures that instance by referring to the instance or its members, you will create a strong reference cycle between the closure and the instance. Swift uses capture lists to break these strong reference cycles. For more information, see Strong Reference Cycles for Closures.”

摘自：Apple Inc.“Swift 编程语言。”电子书。 https://itun.es/us/jEUH0.l

2016 年 1 月 4 日编辑：

引用 Swift 书中解释如何创建捕获列表的部分：

Defining a Capture List: Each item in a capture list is a pairing of the weak or unowned keyword with a reference to a class instance (such as self) or a variable initialized with some value (such as delegate = self.delegate!). These pairings are written within a pair of square braces, separated by commas.

Place the capture list before a closure’s parameter list and return type if they are provided:

lazy var someClosure: (Int, String) -> String = 
{
    [unowned self, weak delegate = self.delegate!] 
    (index: Int, stringToProcess: String) -> String in
    // closure body goes here
}

摘自：Apple Inc.“Swift 编程语言 (Swift 2)。”电子书。 https://itun.es/us/jEUH0.l

如何在块外的 swift 中创建指向自身的弱指针

how to make a weak pointer to self in swift outside of a block

swift

closures

block

weak

2016 年 1 月 4 日编辑：