present出二個modelView之後要dismiss回去rootViewController (iOS5.0之後適用)

if let presentingVC = self?.presentingViewController {

    self?.dismissViewControllerAnimated(false, completion: {

        presentingVC.dismissViewControllerAnimated(false, completion: nil)

    })

}

//這裡的重點是presentingVC是把當下VC給present出來的VC，你也可以看作parentViewController。

而你當前VC所present出來的VC，會叫presentedVC，也可以看作是childrenViewController.

presentingVC ---(present)---> yourViewController ---(present)---> presentedVC