最近在實現iPhone X的適配過程中偶遇了一個問題，push的過程中tabbar的位置會往上移動

QQ20171018-112736-HD.gif

解決方法：
創建一BaseNavigationController繼承于UINavigationController，重寫pushViewController代理方法：

- (void)pushViewController:(UIViewController *)viewController animated:(BOOL)animated {
    [super pushViewController:viewController animated:animated];
//改tabBar的frame
    CGRect frame = self.tabBarController.tabBar.frame;
    frame.origin.y = [UIScreen mainScreen].bounds.size.height - frame.size.height;
    self.tabBarController.tabBar.frame = frame;
}