On Jan 21, 2013, at 2:20 PM, Rick Aurbach <r...@aurbach.com> wrote:
> I am attempting to use the RTPTimer wrapper that Gordon Apple contributed to
> this list. (Thanks, Gordon!)
>
> It appears to work great, but I find that the class's executeSelector: method
> generates a warning message.
>
>> - (void) executeSelector:(NSTimer*)timer {
>> if(self.target != nil) {
>> if([self.target respondsToSelector:self.sel])
>> [self.target performSelector:self.sel withObject:self];
>> }
>> else
>> [self invalidate];
>> }
>
> where sel is defined as @property(nonatomic) SEL sel;
>
> The line containing the performSelector:withObject: method generates
> "PerformSelector may cause a leak because its selector is unknown".
>
> Ok, I agree that the selector is unknown, but we know from the previous line
> that the target responds to it. So I'd like to prevent this particular
> warning. I'm sure I ought to know how do do this, but how do I go about
> removing this warning message? Ideally, I'd like to do this on a file (or
> occurrence) basis, so that I can make sure that other similar usages are
> similarly safe.
The reason it gives that warning is because you're using ARC. Because ARC uses
selector naming conventions to determine certain behaviors, such as whether an
object returned from a method should be retained or not, if ARC doesn't know
what selector is actually being used here, it doesn't know how it should manage
memory for any object returned from this method, conceivably resulting in
crashes or leaks.
I'd suggest you have a look at dispatch_after instead of NSTimer — it uses a
more modern blocks-based interface instead of the old target/selector stuff,
which is often easier to use than target/selector as well as being more
flexible and compatible with both ARC and Xcode's Refactor feature (it's very
annoying to refactor a method only to get unexpected runtime exceptions later
because something was calling the method via @selector, and the refactor
process didn't pick it up).
Charles
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