UINavigationController *na
na.rootVC = vcA;
vcA push vcB;
vcB present vcC;
vcC present vcD;
这时
na.topViewController = vcB;
na.visibleViewController = vcC;
vcD.presentedViewController = nil;
vcD.presentingViewController = vcC;
UINavigationController *na
na.rootVC = vcA;
vcA push vcB;
vcB present vcC;
vcC present vcD;
这时
na.topViewController = vcB;
na.visibleViewController = vcC;
vcD.presentedViewController = nil;
vcD.presentingViewController = vcC;