NSInvocation cleans code

Update: (2008-08-07)

There's been a small (but potent) bug in the given implementation. I somehow move the release of the invocation:


[myInvocation release]; myInvocation = nil;

into the dealloc method of the _UFLatePerformer class. This is bollocks, because the invocation contains _UFLatePerformer as target itself. Therefore I have to release the invocation as soon as it has been invoked. Otherwise there is a retain-cycle and the dealloc-method of _UFLatePerformer is never called.
The code below has been updated accordingly.

During the development of Nifty Box I've grown to use NSInvocations more and more. One thing I am using this class especially for is a wrapper for NSObject's performSelector:withObject:afterDelay:. This method invokes the selector with one argument after a specified delay. My problem was that I can only pass one argument for the selector, but it often happens that I want to invoke a method with more than one argument. So I had to pack all the arguments into a NSDictionary, write a proxy method, inside this proxy function unpack the arguments from the dictionary and invoke the original method. This is messy.

For this I have written a small category add-on for NSObject:

@interface _UFLatePerformer : NSObject {
NSInvocation *myInvocation;
id target;
}
-(id)initWithTarget:(id)theTarget;
-(void)performLate;
@end

@interface NSObject (NSObject_laterInvocation)
-(id)performAfterDelay:(NSTimeInterval)delay;
@end

@implementation _UFLatePerformer

- (id) initWithTarget:(id)theTarget {
[super init];
if (self != nil) {
   target = theTarget;
   [target retain];
}
return self;
}

- (void) dealloc {
[target release]; target = nil;

[super dealloc];
}


-(void)forwardInvocation:(NSInvocation *)invocation;
{
myInvocation = invocation;
[myInvocation retain];
[myInvocation retainArguments];
}

-(BOOL)respondsToSelector:(SEL)aSelector;
{
BOOL result = [super respondsToSelector:aSelector];
if (result == NO)
   result = [target respondsToSelector:aSelector];
return result;
}

-(NSMethodSignature*)methodSignatureForSelector:(SEL)aSelector;
{
NSMethodSignature *result = [super methodSignatureForSelector:aSelector];
if (!result)
   result = [target methodSignatureForSelector:aSelector];
return result;
}


-(void)performLate;
{
[myInvocation invokeWithTarget:target];
[myInvocation release]; myInvocation = nil;
}

@end


@implementation NSObject (NSObject_laterInvocation)

-(id)performAfterDelay:(NSTimeInterval)delay;
{
_UFLatePerformer *latePerformer = [[_UFLatePerformer alloc]
       initWithTarget:self];
[latePerformer performSelector:@selector(performLate)
       withObject:nil afterDelay:delay];
[latePerformer release];
return latePerformer;
}

@end

This basically works like the NSUndoManager's [[undoManager prepareWithInvocationTarget:self] myMethod:someArgument anotherArgument:secondArgument]

You use this new method like that:

[[myObject performAfterDelay:0.0] someMehodWithArgument1:argument1 argument2:argument2]


This is an implementation of the Trampoline Object.

Feel free to use this snippet as you wish. No warranty however.