The canvas listening to many specific objects.

C4WorkSpace.m

//
//  C4WorkSpace.m
//  Notification Tutorial
//
//  Created by Travis Kirton.
//

#import "C4WorkSpace.h"

@implementation C4WorkSpace

-(void)setup {
    C4Shape *s1 = [C4Shape ellipse:CGRectMake(0, 0, 192, 192)];
    C4Shape *s2 = [C4Shape ellipse:s1.frame];
    C4Shape *s3 = [C4Shape ellipse:s1.frame];

    s1.center = CGPointMake(self.canvas.center.x, self.canvas.height * 0.25f);
    s2.center = self.canvas.center;
    s3.center = CGPointMake(self.canvas.center.x, self.canvas.height * 0.75f);
    
    [self.canvas addObjects:@[s1,s2,s3]];

    [self listenFor:@"touchesBegan" fromObjects:@[s1,s2,s3] andRunMethod:@"react"];
}

-(void)react {
    self.canvas.backgroundColor = [UIColor colorWithWhite:[C4Math randomInt:100]/100.0f alpha:1.0f];
}

@end