移动完之后，要以圆形扩散显示出push之后的界面。就可以通过UIBezierPath和CAShapeLayer来实现。UIBezierPath表示路径，CAShapeLayer可以根据路径来显示区域，那么我们可以以第一个界面的视图先看看效果。
UIBezierPath *path = [UIBezierPath bezierPathWithRect:self.collectionView.bounds];
[path appendPath:[UIBezierPath bezierPathWithArcCenter:self.collectionView.center radius:50 startAngle:0 endAngle:2*M_PI clockwise:NO]];
CAShapeLayer *layer = [CAShapeLayer layer];
layer.path = path.CGPath;
self.collectionView.layer.mask = layer;
初始化path路径以collectionView的四边画一个路径，然后加入一个以collectionView的中心为圆点，半径为50的路径，显示的区域就为两个路径之间的区域。
然后再把代码中的radius大小设为200
现在，我们创建一个CABasicAnimation对象去完成扩散的动画，起始位置是半径为10的圆，终点位置是半径为200的圆.
UIBezierPath *path = [UIBezierPath bezierPathWithRect:self.collectionView.bounds];
[path appendPath:[UIBezierPath bezierPathWithArcCenter:self.collectionView.center radius:10 startAngle:0 endAngle:2*M_PI clockwise:NO]];
UIBezierPath *path2 = [UIBezierPath bezierPathWithRect:self.collectionView.bounds];
[path2 appendPath:[UIBezierPath bezierPathWithArcCenter:self.collectionView.center radius:200 startAngle:0 endAngle:2*M_PI clockwise:NO]];
CAShapeLayer *layer = [CAShapeLayer layer];
self.collectionView.layer.mask = layer;
CABasicAnimation *pathAnimation = [CABasicAnimation animationWithKeyPath:@"path"];
pathAnimation.fromValue = (__bridge id)path.CGPath;
pathAnimation.toValue = (__bridge id)path2.CGPath;
pathAnimation.duration = 1.0;
pathAnimation.repeatCount = 1;
pathAnimation.removedOnCompletion = NO;
pathAnimation.fillMode = kCAFillModeForwards;
pathAnimation.timingFunction = [CAMediaTimingFunction functionWithName:kCAMediaTimingFunctionEaseOut];
[layer addAnimation:pathAnimation forKey:@"pathAnimate"];
现在就可以完成push的 转场效果了。注意圆圈白色部分显示的是collectionView底部的self.view的视图。
//加入收合动画
- (void)addPathAnimateWithView:(UIView *)toView fromPoint:(CGPoint)point{
//create path
UIBezierPath *path = [UIBezierPath bezierPathWithRect:CGRectMake(0, 0, k_SF_SCREEN_WIDTH, k_SF_SCREEN_HIGHT)];
//create path
[path appendPath:[UIBezierPath bezierPathWithArcCenter:point radius:0.1 startAngle:0 endAngle:2*M_PI clockwise:NO]];
CGFloat radius = point.y > 0?k_SF_SCREEN_HIGHT*3/4: k_SF_SCREEN_HIGHT*3/4-point.y;
UIBezierPath *path2 = [UIBezierPath bezierPathWithRect:CGRectMake(0, 0, k_SF_SCREEN_WIDTH, k_SF_SCREEN_HIGHT)];
[path2 appendPath:[UIBezierPath bezierPathWithArcCenter:point radius:radius startAngle:0 endAngle:2*M_PI clockwise:NO]];
CAShapeLayer *shapeLayer = [CAShapeLayer layer];
//shapeLayer.path = path.CGPath;
toView.layer.mask = shapeLayer;
CABasicAnimation *pathAnimation = [CABasicAnimation animationWithKeyPath:@"path"];
pathAnimation.fromValue = _type == animate_push? (__bridge id)path.CGPath:(__bridge id)path2.CGPath;
pathAnimation.toValue = _type == animate_push? (__bridge id)path2.CGPath:(__bridge id)path.CGPath;
pathAnimation.duration = _duration/3;
pathAnimation.repeatCount = 1;
pathAnimation.removedOnCompletion = NO;
pathAnimation.fillMode = kCAFillModeForwards;
pathAnimation.timingFunction = [CAMediaTimingFunction functionWithName:kCAMediaTimingFunctionEaseOut];
[shapeLayer addAnimation:pathAnimation forKey:@"pathAnimate"];
}
