动画组

CABasicAnimation和CAKeyframeAnimation仅仅作用于单独的属性，而CAAnimationGroup可以把这些动画组合在一起。CAAnimationGroup是另一个继承于CAAnimation的子类，它添加了一个animations数组的属性，用来组合别的动画。我们把清单8.6那种关键帧动画和调整图层背景色的基础动画组合起来（清单8.10），结果如图8.3所示。

清单8.10 组合关键帧动画和基础动画

- (void)viewDidLoad
{
    [super viewDidLoad];
    //create a path
    UIBezierPath *bezierPath = [[UIBezierPath alloc] init];
    [bezierPath moveToPoint:CGPointMake(0, 150)];
    [bezierPath addCurveToPoint:CGPointMake(300, 150) controlPoint1:CGPointMake(75, 0) controlPoint2:CGPointMake(225, 300)];
    //draw the path using a CAShapeLayer
    CAShapeLayer *pathLayer = [CAShapeLayer layer];
    pathLayer.path = bezierPath.CGPath;
    pathLayer.fillColor = [UIColor clearColor].CGColor;
    pathLayer.strokeColor = [UIColor redColor].CGColor;
    pathLayer.lineWidth = 3.0f;
    [self.containerView.layer addSublayer:pathLayer];
    //add a colored layer
    CALayer *colorLayer = [CALayer layer];
    colorLayer.frame = CGRectMake(0, 0, 64, 64);
    colorLayer.position = CGPointMake(0, 150);
    colorLayer.backgroundColor = [UIColor greenColor].CGColor;
    [self.containerView.layer addSublayer:colorLayer];
    //create the position animation
    CAKeyframeAnimation *animation1 = [CAKeyframeAnimation animation];
    animation1.keyPath = @"position";
    animation1.path = bezierPath.CGPath;
    animation1.rotationMode = kCAAnimationRotateAuto;
    //create the color animation
    CABasicAnimation *animation2 = [CABasicAnimation animation];
    animation2.keyPath = @"backgroundColor";
    animation2.toValue = (__bridge id)[UIColor redColor].CGColor;
    //create group animation
    CAAnimationGroup *groupAnimation = [CAAnimationGroup animation];
    groupAnimation.animations = @[animation1, animation2]; 
    groupAnimation.duration = 4.0;
    //add the animation to the color layer
    [colorLayer addAnimation:groupAnimation forKey:nil];
}