在iOS開(kāi)發(fā)中峻堰，用UINavigationController可以push出一個(gè)界面（UIViewController)挽铁，但不能push出一個(gè)UINavigationController。
如果嘗試下這么做霜旧，應(yīng)用會(huì)拋出異常撩穿，并給出log提示：

reason: 'Pushing a navigation controller is not supported'

因?yàn)橐恍┢婀值漠a(chǎn)品、交互需求萍倡，或者是舊有的界面層級(jí)問(wèn)題，非要在一個(gè)已有的UINavigationController中以從左到右的動(dòng)畫(huà)方式（即系統(tǒng)默認(rèn)的push動(dòng)畫(huà)樣式）展示一個(gè)UINavigationController辟汰，該如何實(shí)現(xiàn)呢列敲？

解決思路：

UINavigationController雖然不可以push另一個(gè)UINavigationController，但是可以通過(guò)以下兩種方式“展示”另一個(gè)UINavigationController：

1. addChildViewController直接add一個(gè)UINavigationController帖汞，并將其view也add到原有的UINavigationController的view層級(jí)上戴而；
2. presentViewController方式present出一個(gè)完整的UINavigationController結(jié)構(gòu)；

上面兩種方式都可以作為解決思路翩蘸，進(jìn)行自定義動(dòng)畫(huà)所意，實(shí)現(xiàn)這個(gè)“Pushing a navigation controller”的需求。
第一種方式?jīng)]嘗試過(guò)催首，可能會(huì)在UINavigationBar顯示等方面出現(xiàn)坑扶踊。
第二種方式的presentViewController已有成熟的自定義動(dòng)畫(huà)、手勢(shì)API支持郎任，實(shí)現(xiàn)起來(lái)更方便秧耗，本文將以第二種方式實(shí)現(xiàn)該效果。

實(shí)現(xiàn)要求：

• 將present動(dòng)畫(huà)自定義為系統(tǒng)原生push樣式的動(dòng)畫(huà)舶治；
• 支持手指跟隨的右滑返回手勢(shì)分井；
• present后，兩個(gè)UINavigationController原有返回手勢(shì)不受影響霉猛；

實(shí)現(xiàn)效果：

實(shí)現(xiàn)步驟：

自定義present動(dòng)畫(huà)

• 分別為present和dismiss創(chuàng)建實(shí)現(xiàn)了UIViewControllerAnimatedTransitioning協(xié)議的動(dòng)畫(huà)類(lèi)：PPTransitionPresenPushStyleAnimator及PPTransitionDismissPopStyleAnimator韩脏。

- (void)animateTransition:(id <UIViewControllerContextTransitioning>)transitionContext

在UIViewControllerAnimatedTransitioning協(xié)議的上面這個(gè)回調(diào)中缩麸，從transitionContext對(duì)象可獲取present和dissmiss相關(guān)的兩個(gè)UIViewController，以及動(dòng)畫(huà)的畫(huà)布——containerView，在回調(diào)內(nèi)完成自定義的動(dòng)畫(huà)杭朱，PPTransitionDismissPopStyleAnimator的實(shí)現(xiàn)如下：

#define kPPTransitionDismissPopStyleDuration 0.3

@implementation PPTransitionDismissPopStyleAnimator

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

- (void)animateTransition:(id<UIViewControllerContextTransitioning>)transitionContext {
    UIViewController *fromVC = [transitionContext viewControllerForKey:UITransitionContextFromViewControllerKey];
    UIViewController *toVC = [transitionContext viewControllerForKey:UITransitionContextToViewControllerKey];
    UIView *container = [transitionContext containerView];
    
    CGFloat screenWidth = [UIScreen mainScreen].bounds.size.width;
    CGRect fromVCRect = fromVC.view.frame;
    fromVCRect.origin.x = 0;
    fromVC.view.frame = fromVCRect;
    
    [container addSubview:toVC.view];
    CGRect toVCRect = toVC.view.frame;
    toVCRect.origin.x = -screenWidth;
    toVC.view.frame = toVCRect;
    
    fromVCRect.origin.x = screenWidth;
    toVCRect.origin.x = 0;
    
    [UIView animateWithDuration:[self transitionDuration:transitionContext] animations:^{
        fromVC.view.frame = fromVCRect;
        toVC.view.frame = toVCRect;
    } completion:^(BOOL finished){
        [transitionContext completeTransition:![transitionContext transitionWasCancelled]];//動(dòng)畫(huà)結(jié)束阅仔、取消必須調(diào)用
    }];
}
@end

PPTransitionDismissPopStyleAnimator實(shí)現(xiàn)也與之類(lèi)似，具體見(jiàn)源碼弧械。

• 調(diào)用presentViewController:animated:completion:消息的類(lèi)八酒，需要實(shí)現(xiàn)UIViewControllerTransitioningDelegate協(xié)議，以返回剛才定義的自定義動(dòng)畫(huà)對(duì)象刃唐。

- (nullable id <UIViewControllerAnimatedTransitioning>)animationControllerForPresentedController:(UIViewController *)presented
                                                                            presentingController:(UIViewController *)presenting
                                                                                sourceController:(UIViewController *)source {
    return [PPTransitionPresenPushStyleAnimator new];
}

- (nullable id <UIViewControllerAnimatedTransitioning>)animationControllerForDismissedController:(UIViewController *)dismissed {
    return [PPTransitionDismissPopStyleAnimator new];
}

自定義返回手勢(shì)

• 為即將被present出來(lái)的view添加UIScreenEdgePanGestureRecognizer手勢(shì)作為返回操作手勢(shì)羞迷。
  該類(lèi)型手勢(shì)與UINavigationController自帶的返回手勢(shì)interactivePopGestureRecognizer是同一類(lèi)型，二者應(yīng)該是互斥的画饥，同一時(shí)間只識(shí)別其中一個(gè)衔瓮。所以添加時(shí)需增加requireGestureRecognizerToFail的邏輯：

UIScreenEdgePanGestureRecognizer *screenGesture = [[UIScreenEdgePanGestureRecognizer alloc] initWithTarget:self action:@selector(onPanGesture:)];
screenGesture.delegate = self;
screenGesture.edges = UIRectEdgeLeft;
[viewControllerToPresent.view addGestureRecognizer:screenGesture];
if ([viewControllerToPresent isKindOfClass:[UINavigationController class]]) {
        [screenGesture requireGestureRecognizerToFail:((UINavigationController*)viewControllerToPresent).interactivePopGestureRecognizer];
}

• 實(shí)現(xiàn)pan手勢(shì)手指跟隨，即手指從左向右邊滑動(dòng)后抖甘，又向左邊屏幕滑動(dòng)热鞍，則需要取消此次的dismiss操作。
  UIViewControllerTransitioningDelegate的回調(diào)接口已有對(duì)這種情況的支持衔彻，只需要返回在下面兩個(gè)回調(diào)中薇宠，返回一個(gè)實(shí)現(xiàn)UIViewControllerInteractiveTransitioning協(xié)議的對(duì)象即可。

- (nullable id <UIViewControllerInteractiveTransitioning>)interactionControllerForPresentation:(id <UIViewControllerAnimatedTransitioning>)animator;

- (nullable id <UIViewControllerInteractiveTransitioning>)interactionControllerForDismissal:(id <UIViewControllerAnimatedTransitioning>)animator;

而系統(tǒng)自帶的UIPercentDrivenInteractiveTransition類(lèi)已實(shí)現(xiàn)該協(xié)議艰额，它的功能描述如下：

A percent-driven interactive transition object drives the custom animation between the disappearance of one view controller and the appearance of another.

所以此處使用UIPercentDrivenInteractiveTransition類(lèi)完成這個(gè)進(jìn)度相關(guān)的判斷澄港，將UIPercentDrivenInteractiveTransition對(duì)象以屬性方式聲明在ViewController中。

@property (nonatomic, strong) UIPercentDrivenInteractiveTransition *percentDrivenTransition;

在pan手勢(shì)處理的方法中完成對(duì)該屬性的初始化和邏輯處理：

- (void)onPanGesture:(UIScreenEdgePanGestureRecognizer *)gesture {
    float progress = [gesture translationInView:self.view].x / [UIScreen mainScreen].bounds.size.width;
    if (gesture.state == UIGestureRecognizerStateBegan) {
        self.percentDrivenTransition = [UIPercentDrivenInteractiveTransition new];
        [self dismissViewControllerAnimated:YES completion:NULL];
    } else if (gesture.state == UIGestureRecognizerStateChanged) {
        [self.percentDrivenTransition updateInteractiveTransition:progress];
    } else if (gesture.state == UIGestureRecognizerStateCancelled ||
               gesture.state == UIGestureRecognizerStateEnded) {
        if (progress > 0.5) {
            [self.percentDrivenTransition finishInteractiveTransition];
        } else {
            [self.percentDrivenTransition cancelInteractiveTransition];
        }
        self.percentDrivenTransition = nil;
    }
}

至此柄沮，就完成了自定義push樣式的present動(dòng)畫(huà)回梧。
Demo下載