performSelector with more than 2 objects

Question

Is there a way to call [anObject performSelector]; with more than 2 objects? I know you can use an array to pass multiple arguments, but I was wondering if there was a lower level way to call a function I already have defined with more that 2 arguments without using a helper function with an nsarray of arguments.

Phage

Answer 1

Either (1) Use an NSInvocation or (2) directly use objc_msgSend.

objc_msgSend(target, @selector(action:::), arg1, arg2, arg3);

(Note: make sure all arguments are id's, otherwise the arguments might not be sent correctly.)

Asthenic

When using objc_msgSend, you'll need to #import <objc/message.h> as per: #4897010 – Ostraw

that last note you made about making sure all args are of type id's.. can you explain further? or provide some resource please? i cant find any. – Equites

Answer 2

You can extend the NSObject class like this:

- (id) performSelector: (SEL) selector withObject: (id) p1
       withObject: (id) p2 withObject: (id) p3
{
    NSMethodSignature *sig = [self methodSignatureForSelector:selector];
    if (!sig)
        return nil;

    NSInvocation* invo = [NSInvocation invocationWithMethodSignature:sig];
    [invo setTarget:self];
    [invo setSelector:selector];
    [invo setArgument:&p1 atIndex:2];
    [invo setArgument:&p2 atIndex:3];
    [invo setArgument:&p3 atIndex:4];
    [invo invoke];
    if (sig.methodReturnLength) {
        id anObject;
        [invo getReturnValue:&anObject];
        return anObject;
    }
    return nil;
}

(See NSObjectAdditions from the Three20 project.) Then you could even extend the above method to use varargs and nil-terminated array of arguments, but that’s overkill.

Dark

Answer 3

An additional option, when you require to send multiple objects with performSelector is (if it's easy enough to do) to amend the method you wish to call to take an NSDictionary object instead of multiple parameters, as you'll be able to send as many as you like within the dictionary.

For example

I had a method similar to this which had 3 arguments and I needed to call it from performSelector -

-(void)getAllDetailsForObjectId:(NSString*)objId segment:(Segment*)segment inContext:(NSManagedObjectContext*)context{

I changed this method to make use of a dictionary to store the arguments

-(void)getAllDetailsForObject:(NSDictionary*)details{

therefore I was able to call the method easily

[self performSelector:@selector(getAllDetailsForObject:) withObject:@{Your info stored within a dictionary}];

Thought I'd be as well sharing this as an alternative option as it works for me.

Cheers

Ancestry