Viewの周りに余白(margin)を付けて枠線を付ける

gistfile1.m

    CGFloat margin = 3.0;
    CGFloat w = aView.bounds.size.width;
    CGFloat h = aView.bounds.size.height;
    
    CALayer *borderLayer = [CALayer layer];
    borderLayer.borderColor = [UIColor lightGrayColor].CGColor;
    borderLayer.borderWidth = 1;
    borderLayer.frame = CGRectMake(-margin, -margin, w + margin * 2, h + margin * 2);
    
    [aView.layer addSublayer:borderLayer];