Question

So I am doing this to initialize my selector:

//In .h

SEL selectors[3];

//In .m

selectors[0] = @selector(rotate);
selectors[1] = @selector(discharge);

And here is the problem:

When I call this in my init method in Cocos2d like this:

[self performSelector:selectors[0]];

it works fine, but when I call this line of code in a method called moveThings which is invoked through the schedule ([self schedule:@selector(moveThings:)]) at the end of my init method in Cocos2d it gives EXC_BAD_ACCESS. What is the problem with scheduling things?

UPDATE:

I have found there is a problem with the rotate function (the function being stored in selector[0]). Here it is:

-(void)rotate:(ccTime)delta {
    if (((CCSprite *)[creature objectAtIndex:0]).rotation < 360) {
        ((CCSprite *)[creature objectAtIndex:0]).rotation++;
    }
    else {
        ((CCSprite *)[creature objectAtIndex:0]).rotation++;
    }
}

If I comment the contents of the method out it works fine when called through moveThings and init.

If I change the methods contents with:

((CCSprite *)[creature objectAtIndex:0]).rotation++;

It fails… But, again, I would like to state that all of these things do work if I call it in my init method, even call it twice in a row, but it will not work (except when I take out the contents of the rotate method) if I call it through the moveThings: method which is being invoke through the schedule method it fails.

Further update:

If I call:

((CCSprite *)[creature objectAtIndex:0]).rotation++;

In moveThings (which is being, as I’ve said before, invoked by the schedule:(SEL) method) it fails. Where as long as it is not invoked through a method that is the called by schedule it works.

Answer 1

The problem is that when you call performSelector there are only two options:

1. have your selector take no arguments and leave the “:” off the @selector(foo) definition.
2. have your selector take either one or two arguments which both must be an NSObject or subclass

it is the latter that is messing you up here I suspect.

Here are the three forms of performSelector:

- (id)performSelector:(SEL)aSelector;
- (id)performSelector:(SEL)aSelector withObject:(id)object;
- (id)performSelector:(SEL)aSelector withObject:(id)object1 withObject:(id)object2;

You’ll note that the withObject arguments are all of type id which is an Objective C object.

The selector you’re trying to use takes a ccTime which is a float and not an Objective C object as it’s param and that is why things are crashing:

-(void)rotate:(ccTime)delta;

One option is to make a wrapper method that takes a wrapped ccTime and unwraps it and calls the rotate:(ccTime) method:

- (void) wrappedRotate: (NSNumber*) inDelta
{
    [self rotate: [inDelta floatValue]];
}

then use

selectors[0] = @selector(wrappedRotate:);

and then call via:

[self schedule: @selector(moveThings:)]);  // cocos2d schedule

... 

- (void) moveThings: (ccTime) dt
{
   [self performSelector: selectors[0] withObject: [NSNumber numberWithFloat: dt]];
  ...
}

One reason you are getting confused is because Cocos2d is using @selector in somewhat more complicated ways (see CCScheduler.m in the CCTimer::initWithTarget:selector:interval: and CCTimer::update: method in particular).

disclaimer: code typed into SO so not checked with a compiler, but the essence of what you need should be here.