UIView动画backgroundColor与drawRect：

Question

我有一个能够在自己上画一个矩形的视图。 它实际上是UICollectionView的子类，但我只是在努力解决UIView特定的问题; backgroundColor。

我只是添加了UIPanGestureRecognizer，将起点保存在UIGestureRecognizerStateBegan，结束点保存在UIGestureRecognizerStateChanged。然后我使用-drawRect:方法绘制实际路径：

- (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);
    }
}

我现在想要在视图闪烁的情况下启动选择模式（rect应该是实际的）。我为此创建了一个UIView动画：

- (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];
        }
    }
}

问题是：一旦我实现了-drawRect:方法，UIView就不再为backgroundColor更改设置动画了。我已经尝试了UIViewAnimationOptionAllowAnimatedContent几乎我在谷歌上找到的所有内容，但我无法解决我的问题。

是否有人知道如何设置UIView的backgroundColor动画并实现-drawRect:？