在这个demo中，核心为选用画布CAShapeLayer，因为一般都是用它来处理形状之类的动画，结合了贝塞尔曲线来控制路径，然后使用CABasicAnimation核心动画来产生所有效果。
首先封装一个自定义的动画。
///动画自定义封装
-(void)animationWithView:(UIView *)view{
//1.创建layer
CAShapeLayer *layer = [[CAShapeLayer alloc]init];
//2.创建贝塞尔路径(参数为圆的外接矩形)
//间距
CGFloat margin = 20;
//半径
CGFloat radius = 25;
//屏幕尺寸
CGFloat viewWidth = [UIScreen mainScreen].bounds.size.width;
//屏幕高度
CGFloat viewHeight = [UIScreen mainScreen].bounds.size.height;
//屏幕对角线
CGFloat endRadius =sqrt(viewHeight*viewHeight +viewWidth*viewWidth);
//起始路径
CGRect startRect = CGRectMake(viewWidth-2*radius-margin, margin, radius*2, radius*2);
UIBezierPath *startPath = [UIBezierPath bezierPathWithOvalInRect:startRect];
//终止路径
UIBezierPath *endPath = [UIBezierPath bezierPathWithOvalInRect:CGRectInset(startRect, -endRadius, -endRadius) ];
//3.设置贝塞尔属性
//填充颜色
layer.fillColor = [UIColor redColor].CGColor;
//4.将贝塞尔作为layer的路径
layer.path = startPath.CGPath;
//将layer作为父视图的遮罩图层.
view.layer.mask = layer;
//5.将path添加到视图中
//[self.view.layer addSublayer:layer];
//使用核心动画实现
CABasicAnimation *animation = [CABasicAnimation animationWithKeyPath:@"path"];
//这个属性是判断是动画之前还是动画之后的。
if (self.isPresent) {
animation.fromValue = (__bridge id _Nullable)(startPath.CGPath);
animation.toValue = (__bridge id _Nullable)(endPath.CGPath);
}else{
animation.fromValue = (__bridge id _Nullable)(endPath.CGPath);
animation.toValue = (__bridge id _Nullable)(startPath.CGPath);
}
animation.delegate = self;
//设置动画属性
animation.fillMode = kCAFillModeForwards;
animation.duration = 2;
animation.removedOnCompletion = NO;
//添加动画到图层
[layer addAnimation:animation forKey:nil];
}! 这里要注意这个mask的属性，设置之后就不需要再额外的add进去，它是一种用于遮罩视图的效果，并且设置的颜色会失效
在这个动画中，有三个重要的属性，号称“转场三剑客”。
UIViewControllerAnimatedTransitioning,主要负责转场的动画时间和动画具体内容。
#pragma mark - UIViewControllerAnimatedTransitioning
///转场动画时间
- (NSTimeInterval)transitionDuration:(nullable id <UIViewControllerContextTransitioning>)transitionContext{
return 2;
}
///转场动画的内容
- (void)animateTransition:(id <UIViewControllerContextTransitioning>)transitionContext{
//1.获取上下文的容器视图
UIView *containerView = transitionContext.containerView;
//2.获取目标视图
UIView *fromView = [transitionContext viewForKey:UITransitionContextFromViewKey];
UIView *toView = [transitionContext viewForKey:UITransitionContextToViewKey];
//3.将目标视图添加到容器视图
UIView *aniView = self.isPresent?toView:fromView;
[containerView addSubview:aniView];
//4.开始动画
[self animationWithView:aniView];
self.context = transitionContext;
}CAAnimationDelegate，主要负责监控动画开始和动画结束之后。
#pragma mark - CAAnimationDelegate
///动画开始
- (void)animationDidStart:(CAAnimation *)anim{
}
///每次动画结束调用
- (void)animationDidStop:(CAAnimation *)anim finished:(BOOL)flag{
//5.告诉上下文完成转场,否则上下文将会一直等待系统通知是否完成.
[self.context completeTransition:YES];
}UIViewControllerTransitioningDelegate，主要负责告诉系统由哪个控制器提供转场，哪个控制器来解除转场。
#pragma mark - UIViewControllerTransitioningDelegate
///告诉由谁提供转场
- (nullable id <UIViewControllerAnimatedTransitioning>)animationControllerForPresentedController:(UIViewController *)presented presentingController:(UIViewController *)presenting sourceController:(UIViewController *)source{
self.isPresent = YES;
return self;
}
///由谁解除转场
- (nullable id <UIViewControllerAnimatedTransitioning>)animationControllerForDismissedController:(UIViewController *)dismissed{
self.isPresent = NO;
return self;
}最后只需要在需要转场的控制器中使用这个封装的类即可
-(void)awakeFromNib{
[super awakeFromNib];
//1.设置跳转样式
self.modalPresentationStyle = UIModalPresentationCustom;
//2.设置代理
self.animation = [[JanCustomAnimation alloc]init];
self.transitioningDelegate = self.animation;
}
-(void)touchesBegan:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event{
[self dismissViewControllerAnimated:YES completion:nil];
}需要注意的是设置样式和代理，必须要优先于viewdidload之前设置，因为这里涉及到控制器的生命周期的问题。
好了，到这里就可以实现完整的自定义转场的酷炫效果了。
