ViewController之间的切换动画

一 、API介绍

iOS7开始，苹果推出了自定义转场动画API。从此，任何可以用Core Animation实现的动画，都可以出现在两个ViewController的切换之间

知识点图：

从上图可以看出，新的Api主要提供了2中VC切换方式，动画式切换，交互式切换。

二 、动画式切换，实现方法：

1，创建继承自NSObject并且声明 UIViewControllerAnimatedTransitioning的动画类；

#import <UIKit/UIKit.h>
@interface PagingTransition : NSObject<UIViewControllerAnimatedTransitioning>

@end

2，重载 UIViewControllerAnimatedTransitioning 中的协议方法。　

#import "PagingTransition.h"

@implementation PagingTransition

//返回动画的时间
- (NSTimeInterval)transitionDuration:(nullable id <UIViewControllerContextTransitioning>)transitionContext
{

    return  ;

}
//在进行切换的时候将调用该方法，我们对于切换时的UIView的设置和动画都在这个方法中完成。
- (void)animateTransition:(id <UIViewControllerContextTransitioning>)transitionContext
{

    UIViewController* toVC = [transitionContext viewControllerForKey:UITransitionContextToViewControllerKey];
    UIViewController* fromVC = [transitionContext viewControllerForKey:UITransitionContextFromViewControllerKey];
    [[transitionContext containerView] addSubview:toVC.view];

    /**
     *  效果1
     */

    toVC.view.alpha = ;

    [UIView animateWithDuration:[self transitionDuration:transitionContext] animations:^{
        fromVC.view.transform = CGAffineTransformMakeScale(0.1, 0.1);
        toVC.view.alpha = ;
    } completion:^(BOOL finished) {
        fromVC.view.transform = CGAffineTransformIdentity;
        [transitionContext completeTransition:![transitionContext transitionWasCancelled]];

    }];

    /**
     *  另一种效果
     */
//    CGRect  finalRect = [transitionContext finalFrameForViewController:toVC];
//
//    toVC.view.frame = CGRectOffset(finalRect, 0, [[UIScreen mainScreen]bounds].size.height);
//
//    [UIView animateWithDuration:[self transitionDuration:transitionContext] delay:0.0 usingSpringWithDamping:0.8 initialSpringVelocity:0.0 options:UIViewAnimationOptionCurveLinear animations:^{
//        toVC.view.frame = finalRect;
//    } completion:^(BOOL finished) {
//        //5
//        [transitionContext completeTransition:YES];
//    }];
//
}

@end

3, 在ViewController中实现 UINavigationControllerDelegate 方法，并指定delegate。

self.navigationController.delegate = self;

#pragma mark--  UINavigationControllerDelegate
- (id<UIViewControllerAnimatedTransitioning>) navigationController:(UINavigationController *)navigationController
     animationControllerForOperation:(UINavigationControllerOperation)operation   fromViewController:(UIViewController*)fromVC
     toViewController:(UIViewController*)toVC
{
    if (operation == UINavigationControllerOperationPush) {
        PagingTransition *ping = [PagingTransition new];
        return ping;
    }
    return nil;
}

三、交互式切换 ，会根据交互式手势来切换VC并同时播放动画效果。

参考： http://www.cocoachina.com/industry/20140623/8918.html

例子：https://github.com/PeteC/InteractiveViewControllerTransitions