Question

I am looking for a class that has an “event list” similar to how UIButton works where you can add multiple targets and selectors.

It’s easy enough to write one, but if Apple has already provided a solution I would rather use this than have more code to maintain.

Note:

This is for a non-visual class, so I don’t really want to use any of the UI specific stuff.

Edit:

I ended up rolling my own rudimentary event dispatcher type class using stacked NSDictionary instances.

@implementation ControllerBase
@synthesize eventHandlers;


- (id) init
{
    self = [super init];

    if (self!=NULL)
    {
        NSMutableDictionary* dict = [[NSMutableDictionary alloc] init];
        [self setEventHandlers: dict];

        [dict release];
    }

    return self;
}


-(void) addTarget: (id) target  action:(SEL) selector  forEvent:(NSString*) eventName
{
    NSString* selectorString =  NSStringFromSelector(selector);   
    NSMutableDictionary* eventDictionary = [eventHandlers objectForKey:eventName];

    if (eventDictionary==NULL)
    {
        eventDictionary = [[NSMutableDictionary alloc] init];
        [eventHandlers setValue:eventDictionary forKey:eventName];
    }

    NSArray* array = [NSArray arrayWithObjects:selectorString,target, nil];
    [eventDictionary setValue:array forKey: [target description]];
}

-(void) removeTarget: (id) target  action:(SEL) selector  forEvent:(NSString*) eventName;
{
    NSMutableDictionary* eventDictionary = [eventHandlers objectForKey:eventName];

    //must have already been removed
    if (eventDictionary!=NULL)
    {
        //remove event
        [eventDictionary removeObjectForKey:target];

        //remove sub dictionary
        if ([eventDictionary count]==0)
        {
            [eventHandlers removeObjectForKey:eventName];
            [eventDictionary release];
        }
    }


}

-(void) fireEvent:(NSString *)eventName
{
     NSMutableDictionary* eventDictionary = (NSMutableDictionary*) [eventHandlers objectForKey:eventName];

    if (eventDictionary!=NULL)
    {
        for(id key in eventDictionary)
        {
            NSArray* eventPair= [eventDictionary valueForKey:key];

            if (eventPair!=NULL)
            {

                NSString* selectorString = (NSString*)[eventPair objectAtIndex:0];

                //remove colon at end
                SEL selector = NSSelectorFromString ( [selectorString substringWithRange: NSMakeRange(0, [selectorString length]-1)] ) ;
                id target = [eventPair objectAtIndex:1];

                [target performSelector:selector];
            }

        }
    }

}

-(void) dealloc
{
    for(id key in eventHandlers) 
    {
        NSMutableDictionary* eventDictionary = (NSMutableDictionary*) [eventHandlers objectForKey:key];

        for(id key in eventDictionary)
        {
            [eventDictionary removeObjectForKey:key];
        }

        [eventDictionary release];

    }

    [eventHandlers release];
    [super dealloc];
}



@end

Answer 1

UIButton is a subclass of UIControl. UIControl manages the target/action list for each control event. It has a predefined set of control events, like UIControlEventTouchUpInside and UIControlEventValueChanged. Each control event is represented by a bit in a mask. The bitmask has four bits reserved for app-defined events (UIControlEventApplicationReserved = 0x0F000000).

If UIControl doesn’t do what you want, you’ll need to roll your own event management.