Swift解决循环引用问题

循环引用一般是存在于block(闭包)里面，是在block(闭包)大括号里面加上[weak self]即可，访问self时候，会有问号出现，弱引用的代表：

 private lazy var popoverAnimation: PLPopoverAnimation = PLPopoverAnimation {[weak self] (presented) in
    self?.titleBtn.isSelected = presented
}