UIViewController

//       177行
@property(nullable,nonatomic,weak,readonly) UIViewController *parentViewController;

//当前控制器present出的子控制器    183行
@property(nullable, nonatomic,readonly) UIViewController *presentedViewController;

//(present出的)当前控制器的父控制器    185行
@property(nullable, nonatomic,readonly) UIViewController *presentingViewController;