OC风格:

ViewControllerA* vc = [ViewControllerA new];
[self presentViewController:vc animated:YES completion:^{
    
}];

[self dismissViewControllerAnimated:YES completion:^{
    
}];

swift:

var vc = ViewControllerA();
self.present(vc, animated: true) {
    
}

self.dismiss(animated: true) {
    
}