viewWillAppear，viewDidAppear未使用pushViewController调用

Question

NewViewController_iPhone *newViewController = [[NewViewController_iPhone alloc] initWithNibName:@"NewViewController_iPhone" bundle:nil];


[self.navigationController pushViewController:newViewController animated:YES];

{p> viewWillAppear:和viewDidAppear:未在NewViewController_iPhone中调用。为什么不呢？