How to enable implicit animation in UIView when doing custom drawing?

I perform custom drawing in my UIView subclass using:

- (void)drawRect:(CGRect)rect;

How can I enable implicit animation when the drawing changes?

Since there were no other suggestions I went ahead with the layer delegate method. Perhaps that's the only option anyway.

So in MyView I created a new CALayer property:

-(CALayer*)stylesLayer
{

    if (_stylesLayer == nil) {

        CALayer *aLayer = [CALayer layer];
        aLayer.frame = CGRectMake(0, 0, self.frame.size.width, self.frame.size.height);

        if ([self respondsToSelector:@selector(setContentScaleFactor:)])
        {
            aLayer.contentsScale = self.contentScaleFactor;
        }


        _stylesLayer = aLayer;
        [_stylesLayer retain];
        [self.layer addSublayer:aLayer];
        [aLayer release];
    }

    return _stylesLayer;
}

And in MyViewController I implemented the delegate method that does the drawing:

-(void)drawLayer:(CALayer *)layer inContext:(CGContextRef)context
{

    // custom drawing code here

}

Now when a certain property changes I update the layer from MyViewController, which implicitly does a cross fade animation.

-(void)setStyles:(NSArray *)styles
{

    [styles retain];
    [_styles release];
    _styles = nil;
    _styles = styles;

    [self.myView.stylesLayer setNeedsDisplay];

}