ios之BlocksKit源码学习1－UIControl

- (void)bk_addEventHandler:(void (^)(id sender))handler forControlEvents:(UIControlEvents)controlEvents
{
    NSParameterAssert(handler);
    
    NSMutableDictionary *events = objc_getAssociatedObject(self, BKControlHandlersKey);
    if (!events) {
        events = [NSMutableDictionary dictionary];
        objc_setAssociatedObject(self, BKControlHandlersKey, events, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
    }

    NSNumber *key = @(controlEvents);
    NSMutableSet *handlers = events[key];
    if (!handlers) {
        handlers = [NSMutableSet set];
        events[key] = handlers;
    }
    
    BKControlWrapper *target = [[BKControlWrapper alloc] initWithHandler:handler forControlEvents:controlEvents];
    [handlers addObject:target];
    [self addTarget:target action:@selector(invoke:) forControlEvents:controlEvents];
}