ARC之解决闭包引起的循环强引用

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copy自：swift2.0官方教程中文版---极客学院版

1.产生闭包之间的循环强引用

直接代码和上图：

class HTMLElement {
	let name: String
	let text: String?
	lazy var asHTML: Void -> String = {
		if let text = self.text {
			return "<\(self.name)>\(text)</\(self.name)>"
		} else {
			return "<\(self.name) />"
		}
	}
	init(name: String, text: String? = nil) {
		self.name = name
		self.text = text
	}
	deinit {
		print("\(name) is being deinitialized")
	}
}

var paragraph: HTMLElement? = HTMLElement(name: "p", text: "hello, world")
print(paragraph!.asHTML())
// prints"hello, world"

注意: 上面的 paragraph 变量定义为 可选HTMLElement ，因此我们可以赋值 nil 给它来演示循环强引用。

class HTMLElement {
	let name: String
	let text: String?
	lazy var asHTML: Void -> String = {
		[unowned self] in // 这里加上占有列表
		if let text = self.text {
			return "<\(self.name)>\(text)</\(self.name)>"
		} else {
			return "<\(self.name) />"
		}
	}
	init(name: String, text: String? = nil) {
		self.name = name
		self.text = text
	}
	deinit {
		print("\(name) is being deinitialized")
	}
}

如果闭包有参数列表和返回类型，把捕获列表放在它们前面：
lazy var someClosure: (Int, String) -> String = {
[unowned self, weak delegate = self.delegate!] (index: Int, stringToProcess: String) -> String in
// closure body goes here
}
如果闭包没有指明参数列表或者返回类型，即它们会通过上下文推断，那么可以把捕获列表和关键字 in 放在闭包最开始的地方：
lazy var someClosure: Void -> String = {
[unowned self, weak delegate = self.delegate!] in
// closure body goes here
}

ARC之解决闭包引起的循环强引用

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原文地址：http://blog.csdn.net/fevershen/article/details/47973547