fatal error: unexpectedly found nil while unwrapping an Optional value - delegate

Question

I am already new in Swift. I run app in simulator. I have list of books, when I click one of them, app shows details about selected book. When I click "Edit Book", change some details and click "Save Book" it paused on line 73

Where is mistake? Why delegate is "nil"? Thanks.

I create protocol and declare "delegate field as follows:

In DetailViewController, I set controller delegate as follows:

This is only the declaration of the delegate variable, nothing gets assigned to the delegate here...where do you you have `delegate = something`? — Ladislav, Oct 21 '17 at 10:48
@Ladislav I have no idea where delegate has been declared. In Main.storyboard delegate shown as Outlet which connected to Master — Samil Mehdiyev, Oct 21 '17 at 11:26

Ahmad F · Accepted Answer · 2017-10-21T09:55:23.780

2

First, make sure you implement object.delegate = self in the class that you want to conform to the delegate.

Also, I would suggest to implement the method calling by the delegate as:

delegate?.editBook(self, editBook: book)

it this case, nothing would happen if the delegate for some reason is nil instead of crashing.

Furthermore, you might want to check this answer to make sure that you are setup the delegate as it should (probably, you missed the third step from the mentioned answer).

edited Oct 21 '17 at 09:55

answered Oct 21 '17 at 09:50

Ahmad F

30,560
17
97
143

Thanks for reply. I do as You suggested and it works. But it is difficult to understand what and why? – Samil Mehdiyev Oct 21 '17 at 11:34
Glad to help. Have you checked the answer I mentioned? – Ahmad F Oct 21 '17 at 11:44

fatal error: unexpectedly found nil while unwrapping an Optional value - delegate

1 Answers1