基于CAKeyframeAnimation环绕闪烁效果(过山车效

先看看效果

需求

这个需求是在为了吸引用户注意到某一个按钮, 或一个View里面的内容提出的. 例如: 滑动解锁按钮, 抽奖按钮等, 恩, 是的, 当你打开一个新的界面的时候, 里面的内容展示比较多的时候, 这样的效果确实能突出重点. 然后我接到需求的时候找了一下相关的知识, 发现没什么思路, 本来知乎上有个人提出的问题跟我的需求很像, 可是没有比较清晰的思路答案, 知乎的问题 iOS 一条线条绕贝塞尔曲线做动画?
直到我看到了这一篇iOS动画进阶 - CAKeyframeAnimation实现过山车动画然后找到了思路

实现

画出两个闪烁点得运动轨迹, 并给两个点设定运动轨迹

-(void)pathWithClockwise:(BOOL)clockwise {
    CGFloat width = self.frame.size.width;
    CGFloat height = self.frame.size.height;
    CGPoint startPointOne = CGPointMake(height * 0.5, 0);//第一个闪烁开始的点
    CGPoint startPointTwo = CGPointMake(width - height * 0.5, height);//第二个闪烁开始的点
    
    //第一个闪烁的运动轨迹
      UIBezierPath *pathOne = [UIBezierPath bezierPath];
    //第二个闪烁的运动轨迹
    UIBezierPath *pathTwo = [UIBezierPath bezierPath];
    if (clockwise) {//顺时针
      
        [pathOne moveToPoint:startPointOne];
        [pathOne addLineToPoint:CGPointMake(width - height * 0.5, 0)];
        [pathOne addArcWithCenter:CGPointMake(self.frame.size.width - height * 0.5, height * 0.5) radius:height * 0.5 startAngle:-M_PI_2 endAngle:M_PI_2 clockwise:clockwise];
        [pathOne addLineToPoint:CGPointMake(height * 0.5, height)];
        [pathOne addArcWithCenter:CGPointMake(height * 0.5, height * 0.5) radius:height * 0.5 startAngle:M_PI_2 endAngle: -M_PI_2 clockwise:clockwise];
        
       
        [pathTwo moveToPoint:startPointTwo];
        [pathTwo addLineToPoint:CGPointMake(height * 0.5, height)];
        [pathTwo addArcWithCenter:CGPointMake(height * 0.5, height * 0.5) radius:height * 0.5 startAngle:M_PI_2 endAngle: -M_PI_2 clockwise:clockwise];
        [pathTwo addLineToPoint:CGPointMake(width - height * 0.5, 0)];
        [pathTwo addArcWithCenter:CGPointMake(self.frame.size.width - height * 0.5, height * 0.5) radius:height * 0.5 startAngle:-M_PI_2 endAngle:M_PI_2 clockwise:clockwise];
    }else {//逆时针
        [pathOne moveToPoint:startPointOne];
        [pathOne addArcWithCenter:CGPointMake(height * 0.5, height * 0.5) radius:height * 0.5 startAngle:-M_PI_2 endAngle:M_PI_2 clockwise:clockwise];
        [pathOne addLineToPoint:startPointTwo];
        [pathOne addArcWithCenter:CGPointMake(self.frame.size.width - height * 0.5, height * 0.5) radius:height * 0.5 startAngle:M_PI_2 endAngle: -M_PI_2 clockwise:clockwise];
        [pathOne addLineToPoint:startPointOne];
        
        
        [pathTwo moveToPoint:startPointTwo];
        [pathTwo addArcWithCenter:CGPointMake(self.frame.size.width - height * 0.5, height * 0.5) radius:height * 0.5 startAngle:M_PI_2 endAngle: -M_PI_2 clockwise:clockwise];
        [pathTwo addLineToPoint:startPointOne];
        [pathTwo addArcWithCenter:CGPointMake(height * 0.5, height * 0.5) radius:height * 0.5 startAngle:-M_PI_2 endAngle:M_PI_2 clockwise:clockwise];
        [pathTwo addLineToPoint:startPointTwo];
    
    }
   
    
    
    //显示的轨迹
    CAShapeLayer *pathLayer = [CAShapeLayer layer];
    pathLayer.path = pathOne.CGPath;
    pathLayer.lineCap = kCALineCapRound;
    pathLayer.strokeColor = [UIColor orangeColor].CGColor;
    pathLayer.lineWidth = 2;
    pathLayer.fillColor = [UIColor clearColor].CGColor;
    [self.layer addSublayer:pathLayer];

    //开始两个闪烁动画
    [self startAnimationWith:pathOne startPostion:startPointOne];
    [self startAnimationWith:pathTwo startPostion:startPointTwo];

}

创建闪烁的点, 根据透明度拼成一条渐变的线段

-(void)startAnimationWith:(UIBezierPath *)path startPostion:(CGPoint)point {
    for (int i = 0; i < 20; i++) {
        //创建粒子
        CALayer *dotLayer = [CALayer layer];
        dotLayer.frame = CGRectMake(point.x, point.y, 4, 4);
        dotLayer.backgroundColor = [UIColor colorWithRed:1.0 green:1.0 blue:1.0 alpha:(1-0.05*i)].CGColor;
        [self.layer addSublayer:dotLayer];
        CAKeyframeAnimation *anim = [self animationWithPath:path withIndex:i];
        [dotLayer addAnimation:anim forKey:nil];
    }

}

然后给线段的每个点执行动画

-(CAKeyframeAnimation *)animationWithPath:(UIBezierPath *)path  withIndex:(int)index{
    //添加帧动画
    CAKeyframeAnimation *anim = [CAKeyframeAnimation animation];
    anim.keyPath = @"position";
    anim.path = path.CGPath;
    anim.repeatCount = MAXFLOAT;
    anim.calculationMode = kCAAnimationPaced;
    //动画速度为匀速
    anim.calculationMode = kCAAnimationCubicPaced;
    //动画角度是否调整
    anim.rotationMode = kCAAnimationRotateAuto;
    anim.fillMode = kCAFillModeForwards;
    anim.removedOnCompletion = NO;
    anim.duration = 1.5;
    anim.beginTime = CACurrentMediaTime() + 0.01 * index;
    anim.timingFunction = [CAMediaTimingFunction functionWithName:kCAMediaTimingFunctionLinear];
    return anim;
}

另外一种思路

本来是想用CAShapeLayer作为运动的线段的, 而不是一个个点拼成的线段. CAShapeLayer上做 " strokeStart" 和 "strokeEnd"结合的. 但是细节看起来很丑, 可能是我处理的不够, 如果你有更好的思路欢迎告诉我.

最后附上 DEMO