iphone - Dismissing a Presented View Controller

Question

I have a theoretic question. Now ?'m reading Apple's ViewController guide.

They wrote:

When it comes time to dismiss a presented view controller, the preferred approach is to let the presenting view controller dismiss it. In other words, whenever possible, the same view controller that presented the view controller should also take responsibility for dismissing it. Although there are several techniques for notifying the presenting view controller that its presented view controller should be dismissed, the preferred technique is delegation.

But I can't explain, why I have to create a protocol in presented VC and add delegate varible, create delegate method in presenting VC for dismissing presented VC, instead of a simple call in presented view controller method

[self dismissViewControllerAnimated:NO completion:nil]?

Why is the first choice better? Why does Apple recommend it?

Answer 1

I think Apple are covering their backs a little here for a potentially kludgy piece of API.

  [self dismissViewControllerAnimated:NO completion:nil]

Is actually a bit of a fiddle. Although you can - legitimately - call this on the presented view controller, all it does is forward the message on to the presenting view controller. If you want to do anything over and above just dismissing the VC, you will need to know this, and you need to treat it much the same way as a delegate method - as that's pretty much what it is, a baked-in somewhat inflexible delegate method.

Perhaps they've come across loads of bad code by people not really understanding how this is put together, hence their caution.

But of course, if all you need to do is dismiss the thing, go ahead.

My own approach is a compromise, at least it reminds me what is going on:

  [[self presentingViewController] dismissViewControllerAnimated:NO completion:nil]

[Swift]

  self.presentingViewController?.dismiss(animated: false, completion:nil)