Swift 循环引用

unowned
unowned要求被捕获的变量不能为nil，所以在closure中使用[unowned self] 必须保证self不能为空，所以当self被释放后再执行closure会导致程序崩溃。

let tapBackground = UITapGestureRecognizer()
tapBackground.rx.event.subscribe(onNext: {[unowned self] _ in
self.view.endEditing(true)
}).disposed(by: disposeBag)
view.addGestureRecognizer(tapBackground)

weak
weak允许被捕获的值为可选型，即可以被捕获的值为nil，当使用[weak self]时需要进行对self进行解包。或者使用
guard let strongSelf = self else { return }

let tapBackground = UITapGestureRecognizer()
tapBackground.rx.event.subscribe(onNext: {[weak self] _ in
self?.view.endEditing(true)
}).disposed(by: disposeBag)
view.addGestureRecognizer(tapBackground)

更多理解可查阅
https://blog.csdn.net/weixin_34191734/article/details/89050930?spm=1001.2101.3001.6661.1&utm_medium=distribute.pc_relevant_t0.none-task-blog-2%7Edefault%7ELandingCtr%7Edefault-1.queryctr&depth_1-utm_source=distribute.pc_relevant_t0.none-task-blog-2%7Edefault%7ELandingCtr%7Edefault-1.queryctr&utm_relevant_index=1