How to refer to navigation controller in Swift?

Question

I have created a UINavigationController object and set it as the window's rootViewController property. The rootViewController of the UINavigationController object is a class called UINavigationMenuViewController. If I want to navigate from UINavigationMenuViewController to UIUserProfileViewController for example, I can use:

navigationController!.pushViewController(userProfileVC, animated: true)

as well as

navigationController?.pushViewController(userProfileVC, animated: true)

The effect seems to be the same. I am wondering what's the difference. I would guess the second way is more secure, and in case I forget to embed the UINavigationMenuViewController object inside the UINavigationController, the app would not crash, comparing to the first case. I guess it's also called optionals chaining, I am just not quite sure as I am still learning Swift.

Please give me some advice.

Answer 1

In case of doubt, it's always safer favoring optional chaining rather than forced unwrapping, for the reason you mentioned: if the variable is nil, it will cause the app to crash.

There are some cases where a crash is a good debugging tool though. If having your navigation controller set to nil, you might want to consider that as a development mistake, so making the app crash would make the mistake more explicit.

Besides that, my recommendation is to always use optional chaining and/or optional binding, and limit usage of forced unwrapping to cases where:

• you are sure an optional is not nil
• you have just checked for not nil
• (as mentioned above) you do want the app to crash if the optional is nil