iOS 连续多次present 之后，想回到最初的viewController

// The view controller that was presented by this view controller or its nearest ancestor.

此视图控制器的视图控制器或其最近的祖先。

@property(nullable, nonatomic,readonly) UIViewController *presentedViewController  NS_AVAILABLE_IOS(5_0);

// The view controller that presented this view controller (or its farthest ancestor.)

提出了这个视图控制器的视图控制器(或其最远的祖先)。

@property(nullable, nonatomic,readonly) UIViewController *presentingViewController NS_AVAILABLE_IOS(5_0);

  [self.presentingViewController.presentingViewController dismissViewControllerAnimated:YES completion:nil];

这句话的意思是找到最远的祖先，dismiss掉。

    iOS控制器堆栈是，最叠层的。最初始的画面dismiss掉，子画面也dismiss。