1.对stroke做动画
stroke的意思是描边，对stroke做动画可以让我们对CAShapeLayer描绘的路径做动画效果，可用于进度条绘制等。
以下是一个进度条例子
// 画背景灰色进度条
CGRect progressRect = CGRectMake(100, 200, 200, 10);
CAShapeLayer *backgroundLayer = [CAShapeLayer layer];
backgroundLayer.frame = progressRect;
backgroundLayer.lineWidth = 10;
backgroundLayer.lineCap = kCALineCapRound;
backgroundLayer.strokeColor = [UIColor grayColor].CGColor;
backgroundLayer.fillColor = [UIColor clearColor].CGColor;
UIBezierPath *backPath = [UIBezierPath bezierPath];
[backPath moveToPoint:CGPointMake(0, 5)];
[backPath addLineToPoint:CGPointMake(200, 5)];
backgroundLayer.path = backPath.CGPath;
[self.view.layer addSublayer:backgroundLayer];
// 画前景黄色进度条
CAShapeLayer *foregroundLayer = [CAShapeLayer layer];
foregroundLayer.frame = progressRect;
foregroundLayer.lineWidth = 8;
foregroundLayer.lineCap = kCALineCapRound;
foregroundLayer.strokeColor = [UIColor yellowColor].CGColor;
foregroundLayer.fillColor = [UIColor clearColor].CGColor;
foregroundLayer.strokeEnd = 0.0f;
UIBezierPath *forePath = [UIBezierPath bezierPath];
[forePath moveToPoint:CGPointMake(.5f, 5.f)];
[forePath addLineToPoint:CGPointMake(199.5f, 5.f)];
foregroundLayer.path = forePath.CGPath;
[self.view.layer addSublayer:foregroundLayer];
// 做动画
NSTimer *timer = [NSTimer scheduledTimerWithTimeInterval:1 repeats:YES block:^(NSTimer * _Nonnull timer) {
CGFloat percent = arc4random() % 100 / 100.f;
POPSpringAnimation *spring = [POPSpringAnimation animationWithPropertyNamed:kPOPShapeLayerStrokeEnd];
spring.toValue = @(percent);
spring.springBounciness = 12.f;
[foregroundLayer pop_addAnimation:spring forKey:nil];
}];
2.利用CAGradientLayer做动画
利用CAGradientLayer做动画，一般都是通过设置某个View的layer的mask来实现的。mask的作用是：根据设置的layer某个点的alpha值来决定该layer这个点的alpha值。
CAGradientLayer的startPoint、endPoint、locations和colors都是可以做动画的。
startPoint和endPoint决定图层颜色渐变的方向，默认是从上往下。
colors决定要渐变的颜色，locations则决定渐变的分界点。这两个数组的count必须是相同的。
- (void)fadeAnimation {
UIImageView *imageView = [[UIImageView alloc] initWithImage:[UIImage imageNamed:@"material"]];
[self.view addSubview:imageView];
CAGradientLayer *gradientLayer = [CAGradientLayer layer];
gradientLayer.frame = CGRectMake(0, -imageView.height / 2, imageView.width, imageView.height * 2);
gradientLayer.colors = @[ (__bridge id)[UIColor clearColor].CGColor, (__bridge id)[UIColor whiteColor].CGColor];
gradientLayer.locations = @[ @(0.0), @(0.25)];
[self.view.layer addSublayer:gradientLayer];
imageView.layer.mask = gradientLayer;
NSLog(@"%f", imageView.width);
CABasicAnimation *anim = [[CABasicAnimation alloc] init];
anim.keyPath = @"locations";
anim.duration = 2;
anim.fromValue = @[ @(0.0), @(0.25)];
anim.toValue = @[ @(0.75), @(1.0)];
anim.repeatCount = 10;
[gradientLayer addAnimation:anim forKey:nil];
}
fadeAnim.png
3.正确的移除动画
removeAllAnimation不能随便调用，当你在remove某个动画之后想要添加其他动画，你会发现无论如何都添加不上去，正确的移除方式是根据你添加动画时候的key来移除对应的动画。
[self.goldOreCatcher.layer removeAnimationForKey:kMiningMachineRotationAnimationKey];
CABasicAnimation *anim = [[CABasicAnimation alloc] init];
anim.keyPath = @"bounds";
anim.duration = 5;// TODO 根据速度计算
CGFloat targetLength = sqrtf(pow(lengthX, 2) + pow(lengthY, 2));
anim.toValue = [NSValue valueWithCGRect:CGRectMake(0, 0, self.goldOreCatcher.width, targetLength)];
anim.timingFunction = [CAMediaTimingFunction functionWithName:kCAMediaTimingFunctionLinear];
anim.removedOnCompletion = NO;
anim.fillMode = kCAFillModeForwards;
[self.goldOreCatcher.layer addAnimation:anim forKey:nil];
