Objective-C extension syntax

Question

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The above SO answer is from here.

My question is :

The suggested code seems to be working as expected. But the problem is Xcode issues a warning against the statement pointed to by the red arrow. The warning is :

Instance method '-scrollViewDidScroll' not found (return type defaults to 'id')

Another issue is '-scrollViewDidScroll' returns "void" and not as 'id' which the compiler assumes.

Wish to get rid of the warning and let the compiler know that the return type is "void".

Hope that somebody could help ...

Thanks for the comment. But do you mean that the syntax was different 3 years ago ? — Stanley, May 21 '13 at 14:53
Note that that is a category, not an extension... As well, that method should be prefixed with something to prevent collisions. — bbum, May 21 '13 at 15:56
Thanks for the comment. Frankly, I thought that category and extension were the same thing. Thanks for pointing that out... — Stanley, May 21 '13 at 22:33

score 5 · Accepted Answer · answered May 21 '13 at 14:52

5

self.delegate should be declared as a id<UIScrollViewDelegate> instance.

answered May 21 '13 at 14:52

PatrickNLT

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Thanks for your kind assistance... The declaration is : @interface Web_View_Delegate : UIViewController :) – Stanley May 21 '13 at 15:28

score 2 · Answer 2 · answered May 21 '13 at 14:53

2

Make sure that the type of the delegate has the public method -scrollViewDidScroll.

answered May 21 '13 at 14:53

Cthutu

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score 1 · Answer 3 · answered May 21 '13 at 14:52

1

Explicit casting probably can solve this problem for you.

answered May 21 '13 at 14:52

Vytautas

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score -3 · Answer 4 · answered May 21 '13 at 17:52

I ran into a similar situation where I was calling a selector on a callback that is set programmatically. It generated a warning since the compiler (correctly) assumed it could not tell if the selector was valid for that object at compile time. I used the following code pattern to suppress the warning, which should also work in your case.

//Suppress compiler warnings
#pragma clang diagnostic push
#pragma clang diagnostic ignored "-Warc-performSelector-leaks"

//Perform method that generates warning
[self.delegate scrollViewDidScroll: scrollView];

//Stop suppressing compiler warnings
#pragma clang diagnostic pop

Objective-C extension syntax

4 Answers4