The document for -[NSInvocation retainArguments] tells me:
"If the receiver hasn’t already done so, retains the target and all
object arguments of the receiver and copies all of its C-string
arguments. ... Newly created NSInvocations don’t retain or copy their
arguments, nor do they retain their targets or copy C strings. You
should instruct an NSInvocation to retain its arguments if you intend
to cache it, since the arguments may otherwise be released before the
NSInvocation is invoked."
So I decided to -retainArguments, and presumed that this meant I was
supposed to release the target and arguments when I was done with
them. But I thought it was odd that the documentation did not say so
explicitly, so I did a little experiment, and learned that -
retainArguments also adds them to the autorelease pool! Presumably (I
hope) this happens when and in the thread where the invocation is
invoked.
The code and results are below. Whether -retainArguments is commented
out or not, the target (Target) and the argument (StringWrapper) both
get deallocced just the same. If -retainArguments is commented out,
the final NSLog() does cause a crash, but that is expected since in
this case the target and argument have not been placed in the
autorelease pool by the action of -retainArguments.
If anyone sees anything wrong with my explanation, please reply. I'm
using NSInvocation alot.
------ CONSOLE OUTPUT ------
2009-07-31 23:08:56.848 Test[48825:10b] retainCounts: target=1
stringWrapper=1
2009-07-31 23:08:56.854 Test[48825:10b] retainCounts: target=2
stringWrapper=2
2009-07-31 23:08:56.860 Test[48825:10b] Hello
2009-07-31 23:08:56.861 Test[48825:10b] retainCounts: target=2
stringWrapper=2
2009-07-31 23:08:56.862 Test[48825:10b] retainCounts: target=1
stringWrapper=1
2009-07-31 23:08:56.864 Test[48825:10b] dealloccing Target
2009-07-31 23:08:56.871 Test[48825:10b] dealloccing MyString
------ CODE ------
#import <Cocoa/Cocoa.h>
@interface StringWrapper :NSObject{
NSString* string ;
}
@property (retain) NSString* string ;
- (id) initWithString:(NSString*)string ;
@end
@implementation StringWrapper
@synthesize string ;
- (id) initWithString:(NSString*)string_ {
self = [super init];
if (self != nil) {
[self setString:string_] ;
}
return self;
}
- (void)dealloc {
NSLog(@"dealloccing MyString") ;
[string release] ;
[super dealloc] ;
}
@end
@interface Target : NSObject {
}
- (void)logThis:(StringWrapper*)what ;
@end
@implementation Target
- (void)logThis:(StringWrapper*)what {
NSLog([what string]) ;
}
- (void)dealloc {
NSLog(@"dealloccing Target") ;
[super dealloc] ;
}
@end
int main (int argc, const char * argv[]) {
NSAutoreleasePool* pool = [[NSAutoreleasePool alloc] init] ;
Target* target = [[Target alloc] init] ;
SEL selector = @selector(logThis:) ;
NSMethodSignature* methSig = [target
methodSignatureForSelector:selector] ;
NSInvocation* invoc = [NSInvocation
invocationWithMethodSignature:methSig] ;
[invoc setTarget:target] ;
[invoc setSelector:selector] ;
StringWrapper* stringWrapper = [[StringWrapper alloc]
initWithString:@"Hello"] ;
[invoc setArgument:&stringWrapper
atIndex:2] ;
NSLog(@"retainCounts: target=%d stringWrapper=%d",
[target retainCount],
[stringWrapper retainCount]) ;
// Here's the retainArguments which may be commented out:
[invoc retainArguments] ;
NSLog(@"retainCounts: target=%d stringWrapper=%d",
[target retainCount],
[stringWrapper retainCount]) ;
[invoc invoke] ;
NSLog(@"retainCounts: target=%d stringWrapper=%d",
[target retainCount],
[stringWrapper retainCount]) ;
[target release] ;
[stringWrapper release] ;
NSLog(@"retainCounts: target=%d stringWrapper=%d",
[target retainCount],
[stringWrapper retainCount]) ;
[pool release] ;
}
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