Swift 闭包中循环引用解决方式

示例说明：开启一个定时器，然后每隔一秒钟加1秒，直到60秒

变量声明

//声明一个定时器变量
var timer: Timer?
var currentSeconds: Int = 0

weak 方式

    func testTimer(){

        weak var weakSelf :  CurrentController? = self
        timer = Timer.scheduledTimer(withTimeInterval: 1.0, repeats: true, block: { _ in

            weakSelf?.currentSeconds += 1

            if weakSelf?.currentSeconds == 60{

                weakSelf?.timer?.invalidate()
                weakSelf?.timer = nil
            }
        })
    }

[weak self] 方式

    func testTimer(){
        timer = Timer.scheduledTimer(withTimeInterval: 1.0, repeats: true, block: {[weak self] (_) in

            self?.currentSeconds += 1

            if self?.currentSeconds == 60{

                self?.timer?.invalidate()
                self?.timer = nil
            }
        })
    }

[unowned self] 方式

    func testTimer(){

        timer = Timer.scheduledTimer(withTimeInterval: 1.0, repeats: true, block: {[unowned self] (_) in

            self.currentSeconds += 1

            if self.currentSeconds == 60{
                self.timer?.invalidate()
                self.timer = nil
            }
        })
    }