CAMediaTimingFunction ：https://github.com/YouXianMing/Tween-o-Matic-CN?spm=5176.100239.blogcont29568.8.hA2dRk 設置動畫的速度變化

- (void)viewDidLoad {

[super viewDidLoad];

// 初始化layer

CALayer *layer? ? ? ? = [CALayer layer];

layer.frame? ? ? ? ? = CGRectMake(50, 50, 200, 2);

layer.backgroundColor = [UIColor blackColor].CGColor;

// 終點位置

CGPoint endPosition = CGPointMake(layer.position.x, layer.position.y + 200);

// 動畫

CABasicAnimation *animation = [CABasicAnimation animationWithKeyPath:@"position"];

animation.fromValue? ? ? ? = [NSValue valueWithCGPoint:layer.position];

animation.toValue? ? ? ? ? = [NSValue valueWithCGPoint:endPosition];

animation.timingFunction? ? = [CAMediaTimingFunction functionWithControlPoints:0.20 :0.03 :0.13 :1.00];

layer.position? ? ? ? ? ? ? = endPosition;

animation.duration? ? ? ? ? = 1.f;

// 添加動畫

[layer addAnimation:animation forKey:nil];

// 添加layer

[self.view.layer addSublayer:layer];

}