UIView animated backgroundColor with drawRect: - ios

Question

I have a view that is able to draw a rect on itself.
It is actually a subclass of UICollectionView but I'm just struggling with UIView specific stuff; the backgroundColor.
I simply added a UIPanGestureRecognizer, saved the start point at UIGestureRecognizerStateBegan and the end point at UIGestureRecognizerStateChanged. I then use the -drawRect: method to draw the actual path:
- (void)awakeFromNib {
UIPanGestureRecognizer *pan = [[UIPanGestureRecognizer alloc] initWithTarget:self action:#selector(panGesture:)];
[self addGestureRecognizer:pan];
}
- (void)panGesture:(UIPanGestureRecognizer *)panRecon {
if([panRecon state] == UIGestureRecognizerBegan) {
startPoint = [panRecon locationInView:self];
}
else if([panRecon state] == UIGestureRecognizerChanged) {
endPoint = [panRecon locationInView:self];
[self setNeedsDisplay];
}
else if([panRecon state] == UIGestureRecognizerEnded /* || failed || cancelled */) {
startPoint = CGPointZero;
endPoint = CGPointZero;
[self setNeedsDisplay];
}
}
- (void)drawRect:(CGRect)rect {
if(!CGPointEqualToPoint(startPoint, CGPointZero) && !CGPointEqualToPoint(endPoint, CGPointZero)) {
CGRect selectionRect = CGRectMake(startPoint.x, startPoint.y, endPoint.x - startPoint.x, endPoint.y - startPoint.y);
[[UIColor colorWithWhite:1.0 alpha:0.3] setFill];
[[UIColor colorWithWhite:1.0 alpha:1.0] setStroke];
CGContextFillRect(UIGraphicsGetCurrentContext(), selectionRect);
CGContextStrokeRect(UIGraphicsGetCurrentContext(), selectionRect);
}
}
I now want to start the selection mode (which the rect should actually be) with the view flashing. I created a UIView animation for that:
- (void)startSelection {
[UIView animateWithDuration:0.2 delay:0.0 options:UIViewAnimationOptionCurveEaseIn animations:^{
[self setBackgroundColor:[UIColor whiteColor]];
} completion:^(BOOL finished){
if(finished) {
[UIView animateWithDuration:0.9 delay:0.0 options:UIViewAnimationOptionCurveEaseOut animations:^{
[self setBackgroundColor:[UIColor blackColor]];
} completion:nil];
}
}
}
The problem is: once I implement the -drawRect: method, UIView does not animate the backgroundColor change anymore. I already tried UIViewAnimationOptionAllowAnimatedContent and almost everything I could find on google, but I wasn't able to solve my problem.
Does anybody know how I can animate backgroundColor of an UIView and have -drawRect: implemented?