CoreAnimation加载动画

CoreAnimation加载动画功能，如我们平时上网页在加载时出现的三个圆在加载的动画效果。该功能用到的主要方法有：NSTimer定时器、对视图进行设置平移和缩放、创建UIBezierPath基于矢量的路径添加画弧方法、关键帧动画CAKeyframeAnimation设置相关属性。
三个圆形加载画面，主要由三个view组成，分别为左中右视图，设置的核心代码为：

//1.初始化centerCir视图
    _centerCir = [[UIView alloc] initWithFrame:CGRectMake(0, 0, Radius, Radius)];
    _centerCir.center = self.view.center;
    _centerCir.layer.cornerRadius = Radius * 0.5;
    _centerCir.layer.masksToBounds = YES;
    _centerCir.backgroundColor = [UIColor orangeColor];
    [self.view addSubview:_centerCir];

    //2.初始化leftCir视图
    _leftCir = [[UIView alloc] initWithFrame:CGRectMake(0, 0, Radius, Radius)];
    _leftCir.center = CGPointMake(_centerCir.center.x - Radius, _centerCir.center.y);
    _leftCir.layer.cornerRadius = Radius * 0.5;
    _leftCir.layer.masksToBounds = YES;
    _leftCir.backgroundColor = [UIColor orangeColor];
    [self.view addSubview:_leftCir];

    //3.初始化rightCir视图
    _rightCir = [[UIView alloc] initWithFrame:CGRectMake(0, 0, Radius, Radius)];
    _rightCir.center = CGPointMake(_centerCir.center.x + Radius, _centerCir.center.y);
    _rightCir.layer.cornerRadius = Radius * 0.5;
    _rightCir.layer.masksToBounds = YES;
    _rightCir.backgroundColor = [UIColor orangeColor];
    [self.view addSubview:_rightCir];

定时器设置核心代码：

    //1.初始化定时器
    _timer = [NSTimer scheduledTimerWithTimeInterval:3
                                              target:self
                                            selector:@selector(timerAction:)
                                            userInfo:nil
                                             repeats:YES];
    [_timer fire];

定时器响应时间核心代码：

//设置动画
    [UIView animateWithDuration:1
                     animations:^{

                         //view以最初位置的中心点进行平移
                         _leftCir.transform = CGAffineTransformMakeTranslation(-Radius, 0);
                         //view以闯入的状态进行缩放0.75倍
                         _leftCir.transform = CGAffineTransformScale(_leftCir.transform, 0.75, 0.75);

                         _rightCir.transform = CGAffineTransformMakeTranslation(Radius, 0);
                         _rightCir.transform = CGAffineTransformScale(_rightCir.transform, 0.75, 0.75);

                         _centerCir.transform = CGAffineTransformScale(_centerCir.transform, 0.75, 0.75);
                     }
                     completion:^(BOOL finished) {

                         [UIView animateWithDuration:1
                                          animations:^{
                                              //设置view的状态为最初状态
                                              _leftCir.transform = CGAffineTransformIdentity;
                                              _centerCir.transform = CGAffineTransformIdentity;
                                              _rightCir.transform = CGAffineTransformIdentity;
                                              [self againAnimation];
                                          }];

                     }];

againAnimation核心代码:

//创建基于矢量的路径，bezierPath可实现任意类型
    UIBezierPath *leftCirPath = [UIBezierPath bezierPath];
    //画弧方法
    [leftCirPath addArcWithCenter:self.view.center      //弧线中心点坐标
                           radius:Radius                //弧线坐在圆的半径
                       startAngle:M_PI                  //弧线开始的角度值， M_PI=180°
                         endAngle:2 * M_PI + 2 * M_PI   //弧线结束的角度值
                        clockwise:NO];                  //是否顺时针

    //定义关键帧动画
    CAKeyframeAnimation *leftCirAnimation = [CAKeyframeAnimation animationWithKeyPath:@"position"];
    //动画路径
    leftCirAnimation.path = leftCirPath.CGPath;
    //速度控制函数，控制动画运行节奏
    /**
        kCAMediaTimingFunctionLinear: 线性，均速
        kCAMediaTimingFunctionEaseIn: 渐进，动画缓慢进入，加速离开
        kCAMediaTimingFunctionEaseOut: 渐出，动画全速进入，减速到达目的地
        kCAMediaTimingFunctionEaseInEaseOut: 渐进渐出，缓慢进入，中间加速，减速到达目的地，默认
     */
    leftCirAnimation.timingFunction = [CAMediaTimingFunction functionWithName:kCAMediaTimingFunctionLinear];
    //动画结束，保持动画最后的状态
    leftCirAnimation.fillMode = kCAFillModeForwards;
    //保持显示动画执行后的状态
    leftCirAnimation.removedOnCompletion = YES;
    //动画重复次数
    leftCirAnimation.repeatCount = 2;
    //动画持续时间
    leftCirAnimation.duration = 1;

    [_leftCir.layer addAnimation:leftCirAnimation forKey:@"cc"];


    UIBezierPath * rightCirPath = [UIBezierPath bezierPath];
    [rightCirPath addArcWithCenter:self.view.center
                            radius:Radius
                        startAngle:0
                          endAngle:M_PI + 2 * M_PI
                         clockwise:NO];

    CAKeyframeAnimation *rightCirAnimation = [CAKeyframeAnimation animationWithKeyPath:@"position"];
    rightCirAnimation.path = rightCirPath.CGPath;
    rightCirAnimation.timingFunction = [CAMediaTimingFunction functionWithName:kCAMediaTimingFunctionLinear];
    rightCirAnimation.fillMode = kCAFillModeForwards;
    rightCirAnimation.removedOnCompletion = YES;
    rightCirAnimation.repeatCount = 2;
    rightCirAnimation.duration = 1;

    [_rightCir.layer addAnimation:rightCirAnimation forKey:@"hh"];