（一二一）核心动画基础

核心动画基于QuartzCore框架，仅仅能用于CALayer，能够实现3D效果。它在子线程中运行动画，不会堵塞主线程。

要实现核心动画，主要使用CABasicAnimation实现单步动画、使用CAKeyframeAnimation实现帧动画。

动画的主要属性有duration、keyPath、value、repeatCount等。

动画运行完成后默认会复位，要取消复位，须要下面两行代码：

anim.removedOnCompletion = NO;
anim.fillMode = kCAFillModeForwards;

利用keyPath指定操作的属性，使用toValue指定变化到的值。

CABasicAnimation *anim = [CABasicAnimation animation];
anim.duration = 0.5f;
anim.keyPath = @"transform";
anim.toValue = [NSValue valueWithCATransform3D:CATransform3DMakeRotation(M_PI, 0, 1, 0)];
anim.repeatCount = 100;
// 动画默认会复位。要取消复位，首先禁止动画移除。然后设置保持新位置。
anim.removedOnCompletion = NO;
anim.fillMode = kCAFillModeForwards;
[_blueView.layer addAnimation:anim forKey:nil];

多个value：

CAKeyframeAnimation *anim2 = [CAKeyframeAnimation animation];
anim2.duration = 0.5f;
anim2.keyPath = @"position";
anim2.repeatCount = 100;
NSValue *p1 = [NSValue valueWithCATransform3D:CATransform3DMakeTranslation(50, 0, 0)];
NSValue *p2 = [NSValue valueWithCATransform3D:CATransform3DMakeTranslation(0, 0, 0)];
NSValue *p3 = [NSValue valueWithCATransform3D:CATransform3DMakeTranslation(-50, 0, 0)];
NSValue *p4 = [NSValue valueWithCATransform3D:CATransform3DMakeTranslation(0, 0, 0)];
anim2.values = @[p1,p2,p3,p4];
anim2.removedOnCompletion = NO;
anim2.fillMode = kCAFillModeForwards;

CAKeyframeAnimation *anim2 = [CAKeyframeAnimation animation];
anim2.duration = 0.5f;
anim2.keyPath = @"position";
anim2.repeatCount = 100;
anim2.removedOnCompletion = NO;
UIBezierPath *path = [UIBezierPath bezierPathWithOvalInRect:CGRectMake(100,100,200,200)];
anim2.path = path.CGPath;
anim2.fillMode = kCAFillModeForwards;