iosobjective-cuibuttonrespondstoselector

respondsToSelector returns YES for "setTitle:" on UIButton but there is no such selector

I'm using respondsToSelector: and most of the time it works fine. But there is one case in which I get wrong result:

UIButton* button = [[UIButton alloc] init];
if([button respondsToSelector:NSSelectorFromString(@"setTitle:")]) // returns YES
{
    // try to call "setTitle:"
}

respondsToSelector: returns YES but there is no setTitle: selector in UIButton class. There is setTitle:forState: selector but this is definitely not the same.

So why does respondsToSelector: return YES?

Solution

  • Responds to selector doesn't just check the public interface, it'll take any method it can find. I don't recall if the early API for UIButton ever exposed the title directly, but internally it's likely called as the state changes.

    Try to only use respondsToSelector: for API that you actually need to verify exists, and note that there is often private API which is later made public and that this can also cause interesting situations...