CALayer的隐式动画

何为隐式动画

隐式动画就是直接改变layer的一些属性时，并没有作动画处理，layer会附带有动画效果，而不是直接瞬间变化，这个动画时间默认是0.25秒。

layer的哪些属性有隐式动画

区分属性是不是具有隐式动画，要看属性定义有没有“Animatable”字样。比如

/* The background color of the layer. Default value is nil. Colors * created from tiled patterns are supported. Animatable. */@property(nullable) CGColorRef backgroundColor;

backgroundColor属性的定义最后标明了Animatable，说明修改它的值会有默认动画效果。

怎样修改隐式动画

一、通过CATransaction
在页面上放了一个layer，通过点击button修改它的颜色

@property (nonatomic,strong) UIView     *backView;@property (nonatomic,strong) CALayer    *colorLayer;@property (nonatomic,strong) UIButton   *changeButton;- (void)viewDidLoad {    [super viewDidLoad];    CGFloat kScreenWidth = [UIScreen mainScreen].bounds.size.width;    _backView = [[UIView alloc] initWithFrame:CGRectMake(kScreenWidth/2-100, 50, 200, 200)];    _backView.backgroundColor = [UIColor whiteColor];    [self.view addSubview:_backView];    _colorLayer = [CALayer layer];    _colorLayer.frame = CGRectMake(50, 50, 100, 100);    _colorLayer.backgroundColor = [UIColor redColor].CGColor;    _colorLayer.borderWidth = 0.5;    _colorLayer.borderColor = [UIColor blackColor].CGColor;    _colorLayer.delegate = self;    [_backView.layer addSublayer:_colorLayer];    _changeButton = [UIButton buttonWithType:UIButtonTypeCustom];    [_changeButton addTarget:self action:@selector(changeColor) forControlEvents:UIControlEventTouchUpInside];    _changeButton.frame = CGRectMake(50, 160, 100, 20);    [_changeButton setTitle:@"Change Color" forState:UIControlStateNormal];    [_changeButton setTitleColor:[UIColor blackColor] forState:UIControlStateNormal];    _changeButton.titleLabel.font = [UIFont systemFontOfSize:10];    _changeButton.titleLabel.textColor = [UIColor blackColor];    _changeButton.layer.cornerRadius = 5;    _changeButton.layer.borderWidth = 0.5;    _changeButton.layer.borderColor = [UIColor blackColor].CGColor;    _changeButton.backgroundColor = [UIColor whiteColor];    [_backView addSubview:_changeButton];}- (void)changeColor{    _colorLayer.backgroundColor = [UIColor blueColor].CGColor;］}

为了修改隐式动画，我们对changeColor作修改

- (void)changeColor{    [CATransaction begin];    [CATransaction setAnimationDuration:2];    _colorLayer.backgroundColor = [UIColor blueColor].CGColor;    [CATransaction commit];}

这样点击改变颜色的隐式动画的时间就被修改为2秒。
CATransaction还提供了禁用隐式动画和设置完成动作等方法。
二、通过layer的actions属性

CATransition *transition = [CATransition animation];    transition.type = @"push";    transition.subtype = @"fromLeft";    _colorLayer.actions = @{@"backgroundColor":transition};

这样在改变颜色的过程中就会附带推进的动画效果。
三、通过手动实现-actionForLayer:(CALayer )layer forKey:(NSString )event方法

_colorLayer.delegate = self;- (nullable id<CAAction>)actionForLayer:(CALayer *)layer forKey:(NSString *)event{    CABasicAnimation *animation = [CABasicAnimation animation];    animation.keyPath = @"backgroundColor";    animation.toValue = (__bridge id)[UIColor blueColor].CGColor;    return animation;}

UIView中的layer是没有隐式动画的

UIView关联的layer的隐式动画是被禁用的，所以如果想要通过改变view.layer的属性来实现动画是行不通的，只能通过UIView动画方法或者显式的添加动画来实现。