示例代碼:

import UIKit

class ViewController: UIViewController {

    // 定義閉包
    var callback:(()->())?

    override func viewDidLoad() {
        super.viewDidLoad()
        // 閉包實(shí)現(xiàn)
        callback = {
            print(weakSelf?.view)
        }
    }

    override func touchesBegan(touches: Set<UITouch>, withEvent event: UIEvent?) {
        // 執(zhí)行閉包
        callback?()
    }

    deinit{
        print("ViewController再見(jiàn)")
    }

}

分析:

當(dāng)前控制器 強(qiáng)引用了閉包
閉包強(qiáng)引用self
A -> B  B -> A

解決循環(huán)引用:

• 方法01(仿照OC的寫(xiě)法) (等同于OC中 __weak)

        weak var weakSelf = self
        
        callback = {
            print(weakSelf?.view)
        }

• 方法02 (等同于OC中 __weak) (iOS時(shí)間- 5.0) 推薦方式

        callback = {[weak self] in
            print(self?.view)
        }

• 方法03 (等同于OC中 __unsafe_unretained)(iOS時(shí)間- 4.0)
  缺點(diǎn):self不是可選項(xiàng),如果self已經(jīng)被釋放,則出現(xiàn)野指針訪(fǎng)問(wèn)

        callback = {[unowned self] in
            print(self.view)
        }