Perform selector may cause leak because select is unknown?

Question

I am using the below code & i am getting warning as

Perform selector may cause leak because select is unknown

Code

SEL _selector = NSSelectorFromString([[arrEffects objectAtIndex:1] valueForKey:@"method"]);
self.mainImageView.image = [self.mainImage performSelector:_selector];

Please tell me who can i get rid of this warning?

possible duplicate of [performSelector may cause a leak because its selector is unknown](http://stackoverflow.com/questions/7017281/performselector-may-cause-a-leak-because-its-selector-is-unknown) — ppaulojr, Sep 29 '15 at 10:31

score 2 · Answer 1 · answered Sep 29 '15 at 09:37

The warning is there for a reason. You can check if mainImage responds to selector before performing it. The warning will not go away, but it is more safe. Something like this:

 SEL _selector = NSSelectorFromString(@"asdf");
    if([self respondsToSelector:_selector])
        [self performSelector:_selector];

score 1 · Answer 2 · edited May 23 '17 at 11:51

The reason for this warning is that with ARC, the runtime needs to know what to do with the result of the method you're calling. The result could be anything: void, int, char, NSString *, id, etc. ARC normally gets this information from the header of the object type you're working with.3

There are really only 4 things that ARC would consider for the return value:4

Ignore non-object types (void, int, etc)
Retain object value, then release when it is no longer used (standard assumption)
Release new object values when no longer used (methods in the init/ copy family or attributed with ns_returns_retained)
Do nothing & assume returned object value will be valid in local scope (until inner most release pool is drained, attributed with ns_returns_autoreleased)

This thread explains it in length.

score -1 · Answer 3 · answered Sep 29 '15 at 10:28

You fix it by getting rid of this awful code. To whoever thought this code was a good idea: No, it's not. It's an attempt at being clever and failing miserably.

You are storing the name of a method somewhere in an array, which is totally unsafe. I recommend you analyse the code, find which selectors are possibly stored, and instead of this awful code you store a block which takes an image as a parameter and returns an image instead of the selector, then call the block.

Perform selector may cause leak because select is unknown?

3 Answers3