首先，支持并感谢@wazrx 的 http://www.jianshu.com/p/45434f73019e和@onevcat 的https://onevcat.com/2013/10/vc-transition-in-ios7/ 对于转场动画的讲解和实现，非常详细，本人也是看过他们的文章后受的启发，快速实现了基于本项目需求的转场动画效果。

效果如下：（gif是我们的美术大师帮忙做的演示动效，实际的效果要比这个好，可通过文章最后链接下载我们的app：柠檬跑步，查看效果）

地图切换.gif

我的需求是两个页面push、pop之间的切换，所以自定义了push的转场动画，首先需要个遵循<UIViewControllerAnimatedTransitioning>协议的管理对象，并实现其两个方法：
XWCircleSpreadTransition.h

#import <UIKit/UIKit.h>

typedef NS_ENUM(NSUInteger, XWCircleSpreadTransitionType) {
    XWCircleSpreadTransitionTypePush = 0,
    XWCircleSpreadTransitionTypePop
};

@interface XWCircleSpreadTransition : NSObject<UIViewControllerAnimatedTransitioning>

@property (nonatomic, assign) XWCircleSpreadTransitionType type;

+ (instancetype)transitionWithTransitionType:(XWCircleSpreadTransitionType)type;
- (instancetype)initWithTransitionType:(XWCircleSpreadTransitionType)type;
@end

XWCircleSpreadTransition.m

#import "XWCircleSpreadTransition.h"

@implementation XWCircleSpreadTransition

+ (instancetype)transitionWithTransitionType:(XWCircleSpreadTransitionType)type{
    return [[self alloc] initWithTransitionType:type];
}

- (instancetype)initWithTransitionType:(XWCircleSpreadTransitionType)type{
    self = [super init];
    if (self) {
        _type = type;
    }
    return self;
}

- (NSTimeInterval)transitionDuration:(id<UIViewControllerContextTransitioning>)transitionContext{
    return 0.7;
}

- (void)animateTransition:(id<UIViewControllerContextTransitioning>)transitionContext{
    switch (_type) {
        case XWCircleSpreadTransitionTypePush:
            [self presentAnimation:transitionContext];
            break;
            
        case XWCircleSpreadTransitionTypePop:
            [self dismissAnimation:transitionContext];
            break;
    }
}

- (void)dismissAnimation:(id<UIViewControllerContextTransitioning>)transitionContext{
    UIViewController *toVC = [transitionContext viewControllerForKey:UITransitionContextToViewControllerKey];
    UIViewController *fromVC = [transitionContext viewControllerForKey:UITransitionContextFromViewControllerKey];
    UIView *containerView = [transitionContext containerView];
    [containerView insertSubview:toVC.view atIndex:0];
    //画两个圆路径
    CGFloat radius = sqrtf(containerView.frame.size.height * containerView.frame.size.height + containerView.frame.size.width * containerView.frame.size.width) / 2;
    UIBezierPath *startCycle = [UIBezierPath bezierPathWithArcCenter:containerView.center radius:radius startAngle:0 endAngle:M_PI * 2 clockwise:YES];
//    UIBezierPath *endCycle =  [UIBezierPath bezierPathWithOvalInRect:temp.mapBtnFrame];
    UIBezierPath *endCycle =  [UIBezierPath bezierPathWithOvalInRect:CGRectMake(0, 0, 0, 0)];
    //创建CAShapeLayer进行遮盖
    CAShapeLayer *maskLayer = [CAShapeLayer layer];
    maskLayer.fillColor = [UIColor greenColor].CGColor;
    maskLayer.path = endCycle.CGPath;
    fromVC.view.layer.mask = maskLayer;
    //创建路径动画
    CABasicAnimation *maskLayerAnimation = [CABasicAnimation animationWithKeyPath:@"path"];
    maskLayerAnimation.delegate = self;
    maskLayerAnimation.fromValue = (__bridge id)(startCycle.CGPath);
    maskLayerAnimation.toValue = (__bridge id)((endCycle.CGPath));
    maskLayerAnimation.duration = [self transitionDuration:transitionContext];
    maskLayerAnimation.delegate = self;
    maskLayerAnimation.timingFunction = [CAMediaTimingFunction  functionWithName:kCAMediaTimingFunctionEaseInEaseOut];
    [maskLayerAnimation setValue:transitionContext forKey:@"transitionContext"];
    [maskLayer addAnimation:maskLayerAnimation forKey:@"path"];
}

- (void)presentAnimation:(id<UIViewControllerContextTransitioning>)transitionContext{
    UIViewController *toVC = [transitionContext viewControllerForKey:UITransitionContextToViewControllerKey];
    UIView *containerView = [transitionContext containerView];
    [containerView addSubview:toVC.view];
    //画两个圆路径
//    UIBezierPath *startCycle =  [UIBezierPath bezierPathWithOvalInRect:fromVC.mapBtnFrame];
    UIBezierPath *startCycle =  [UIBezierPath bezierPathWithOvalInRect:CGRectMake(0, 0, 0, 0)];
    CGFloat x = MAX(100, containerView.frame.size.width - 100);
    CGFloat y = MAX(100, containerView.frame.size.height - 100);
    CGFloat radius = sqrtf(pow(x, 2) + pow(y, 2));
    UIBezierPath *endCycle = [UIBezierPath bezierPathWithArcCenter:containerView.center radius:radius startAngle:0 endAngle:M_PI * 2 clockwise:YES];
    //创建CAShapeLayer进行遮盖
    CAShapeLayer *maskLayer = [CAShapeLayer layer];
    maskLayer.path = endCycle.CGPath;
    //将maskLayer作为toVC.View的遮盖
    toVC.view.layer.mask = maskLayer;

    //创建路径动画
    CABasicAnimation *maskLayerAnimation = [CABasicAnimation animationWithKeyPath:@"path"];
    maskLayerAnimation.delegate = self;
    //动画是加到layer上的，所以必须为CGPath，再将CGPath桥接为OC对象
    maskLayerAnimation.fromValue = (__bridge id)(startCycle.CGPath);
    maskLayerAnimation.toValue = (__bridge id)((endCycle.CGPath));
    maskLayerAnimation.duration = [self transitionDuration:transitionContext];
    maskLayerAnimation.delegate = self;
    maskLayerAnimation.timingFunction = [CAMediaTimingFunction  functionWithName:kCAMediaTimingFunctionEaseInEaseOut];
    
    [maskLayerAnimation setValue:transitionContext forKey:@"transitionContext"];
    [maskLayer addAnimation:maskLayerAnimation forKey:@"path"];
}

- (void)animationDidStop:(CAAnimation *)anim finished:(BOOL)flag{
    switch (_type) {
        case XWCircleSpreadTransitionTypePush:{
            id<UIViewControllerContextTransitioning> transitionContext = [anim valueForKey:@"transitionContext"];
            [transitionContext completeTransition:YES];
            UIView *toView = [transitionContext viewForKey:UITransitionContextToViewKey];
            toView.layer.mask = nil;
            UIViewController *vc = [transitionContext viewControllerForKey:UITransitionContextToViewControllerKey];
            vc.view.layer.mask = nil;
        }
            break;
        case XWCircleSpreadTransitionTypePop:{
            id<UIViewControllerContextTransitioning> transitionContext = [anim valueForKey:@"transitionContext"];
            [transitionContext completeTransition:YES];
            UIViewController *vc = [transitionContext viewControllerForKey:UITransitionContextFromViewControllerKey];
            vc.view.layer.mask = nil;
        }
            break;
    }
}
@end

剩下的就是在ViewControllerA中实现代理<UINavigationControllerDelegate>中的animationControllerForOperation：

#pragma mark -
#pragma mark - UINavigation Delegate
-(id<UIViewControllerAnimatedTransitioning>)navigationController:(UINavigationController *)navigationController animationControllerForOperation:(UINavigationControllerOperation)operation fromViewController:(UIViewController *)fromVC toViewController:(UIViewController *)toVC
{
    
    if (fromVC == self) {
        return [XWCircleSpreadTransition transitionWithTransitionType:XWCircleSpreadTransitionTypePush];
    }
    if (toVC == self) {
        return [XWCircleSpreadTransition transitionWithTransitionType:XWCircleSpreadTransitionTypePop];
    }
    return nil;
}

到此，这个简单的转场动画已经实现完毕，而且动画效果可以自定义成自己想要的展现形式。