iOS动画有隐式和显示之分。隐式动画指的是，无须创建动画对象，只需改变动画层的属性，让核心动画自己去完成动画效果, 例如(CATransaction)。显示动画指的是，需要自己创建和管理动画对象，并且将它们应用到动画层，才能显示动画效果。
CGRectInset: Returns a rectangle that is smaller or larger than the source rectangle, with the same center point.
创建一个矩形框, 以原先frame的center为中心, 可做绕一个圈转的动画:
CGMutablePathRefcurvedPath =CGPathCreateMutable();
CGRectcircleContainer =CGRectInset(self.frontView.frame,self.frontView.bounds.size.width/2-13,self.frontView.bounds.size.width/2-13);
CGPathAddEllipseInRect(curvedPath,NULL, circleContainer);
CAKeyframeAnimation*pathAnimation = [CAKeyframeAnimationanimationWithKeyPath:@"position"];
pathAnimation.calculationMode=kCAAnimationPaced;
pathAnimation.fillMode=kCAFillModeForwards;
pathAnimation.removedOnCompletion=NO;
pathAnimation.repeatCount=INFINITY;
pathAnimation.timingFunction= [CAMediaTimingFunctionfunctionWithName:kCAMediaTimingFunctionLinear];
pathAnimation.duration=5.0;
pathAnimation.path= curvedPath;
CGPathRelease(curvedPath);
CAKeyframeAnimation关键帧动画也可做一系列形变:
CAKeyframeAnimation*scaleY = [CAKeyframeAnimationanimationWithKeyPath:@"transform.scale.y"];
scaleY.duration=1.5;
scaleY.values=@[@1.0,@1.1,@1.0];
scaleY.keyTimes=@[@0.0,@0.5,@1.0];
scaleY.repeatCount=INFINITY;
scaleY.autoreverses=YES;
scaleX.timingFunction= [CAMediaTimingFunctionfunctionWithName:kCAMediaTimingFunctionEaseInEaseOut];
[self.frontView.layeraddAnimation:scaleYforKey:@"scaleYAnimation"];
同理scaleX
