Re: How can I get rid of this warning message?
Re: How can I get rid of this warning message?
- Subject: Re: How can I get rid of this warning message?
- From: Charles Srstka <email@hidden>
- Date: Mon, 21 Jan 2013 14:44:02 -0600
On Jan 21, 2013, at 2:20 PM, Rick Aurbach <email@hidden> 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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