App開發流程之右滑返回手勢功能續

上一篇記錄了利用系統私有變數和方法實現右滑返回手勢功能：http://www.cnblogs.com/ALongWay/p/5893515.html

這篇繼續記錄另一種方案：利用UINavigationController的delegate方法。

核心代理方法有如下兩個：

- (nullable id <UIViewControllerInteractiveTransitioning>)navigationController:(UINavigationController *)navigationController
                          interactionControllerForAnimationController:(id <UIViewControllerAnimatedTransitioning>) animationController NS_AVAILABLE_IOS(7_0);

- (nullable id <UIViewControllerAnimatedTransitioning>)navigationController:(UINavigationController *)navigationController
                                   animationControllerForOperation:(UINavigationControllerOperation)operation
                                                fromViewController:(UIViewController *)fromVC
                                                  toViewController:(UIViewController *)toVC  NS_AVAILABLE_IOS(7_0);

第一個代理方法，要求在視圖控制器變換時候，返回一個實現UIViewControllerInteractiveTransitioning協議的對象，該對象用於控制交互進度和狀態。

UIKit.h/UIViewControllerTransitioning.h中已經準備好了一個這樣的對象，名為UIPercentDrivenInteractiveTransition。

主要關註其如下三個方法：

- (void)updateInteractiveTransition:(CGFloat)percentComplete;//控制交互進度的百分比

- (void)cancelInteractiveTransition;//中途取消交互

- (void)finishInteractiveTransition;//完成交互

可以在一個實現了代理方法的類中，定義一個手勢目標方法來調用上述方法，達到控製作為變數的UIPercentDrivenInteractiveTransition對象的目的。

主要代碼如下：

- (id<UIViewControllerInteractiveTransitioning>)navigationController:(UINavigationController *)navigationController interactionControllerForAnimationController:(id<UIViewControllerAnimatedTransitioning>)animationController
{
    if ([animationController isKindOfClass:[PopAnimation class]])
        return _interactivePopTransition;
    
    return nil;
}

- (id<UIViewControllerAnimatedTransitioning>)navigationController:(UINavigationController *)navigationController animationControllerForOperation:(UINavigationControllerOperation)operation fromViewController:(UIViewController *)fromVC toViewController:(UIViewController *)toVC
{
    if (operation == UINavigationControllerOperationPop)
        return _popAnimation;
    
    return nil;
}

- (void)handlePopGestureOperation:(UIPanGestureRecognizer *)recognizer{
    //將手指在屏幕上的移動距離與屏幕寬度比例作為動畫的進度
    CGPoint translationInScreen = [recognizer translationInView:[UIApplication sharedApplication].keyWindow];
    CGFloat progress = translationInScreen.x / [UIScreen mainScreen].bounds.size.width;
    progress = MIN(1.0, MAX(0.0, progress));
    
    if (recognizer.state == UIGestureRecognizerStateBegan) {
        //新建手勢交互對象
        _interactivePopTransition = [[UIPercentDrivenInteractiveTransition alloc] init];

        //開始執行pop動畫
        [_naviController popViewControllerAnimated:YES];
    }else if (recognizer.state == UIGestureRecognizerStateChanged) {
         //更新進度
        [_interactivePopTransition updateInteractiveTransition:progress];
    }else if (recognizer.state == UIGestureRecognizerStateEnded
              || recognizer.state == UIGestureRecognizerStateCancelled) {
        //手勢結束時如果進度大於一半，那麼就完成pop操作，否則取消
        if (progress > 0.5) {
            [_interactivePopTransition finishInteractiveTransition];
        }else {
            [_interactivePopTransition cancelInteractiveTransition];
        }
        
        //手勢交互結束，清理對象
        _interactivePopTransition = nil;
    }
}

第二個代理方法，要求在操作開始時候，返回一個實現UIViewControllerAnimatedTransitioning協議的對象，該對象實現了動畫內容和執行時間。

該協議有三個方法：

// This is used for percent driven interactive transitions, as well as for container controllers that have companion animations that might need to
// synchronize with the main animation. 
- (NSTimeInterval)transitionDuration:(nullable id <UIViewControllerContextTransitioning>)transitionContext;
// This method can only  be a nop if the transition is interactive and not a percentDriven interactive transition.
- (void)animateTransition:(id <UIViewControllerContextTransitioning>)transitionContext;


@optional

// This is a convenience and if implemented will be invoked by the system when the transition context's completeTransition: method is invoked.
- (void)animationEnded:(BOOL) transitionCompleted;

第一個方法返回動畫時間；第二個方法，可以得到實現了UIViewControllerContextTransitioning協議的對象；第三個方法可選，如果transitionContext對象調用了completeTransition：方法，該代理方法會被調用。

重點是第二個方法的transitionContext對象，其重要的方法如下：

// The view in which the animated transition should take place.
- (nullable UIView *)containerView;//動畫所在的容器view
- (BOOL)transitionWasCancelled;//轉換是否取消// This must be called whenever a transition completes (or is cancelled.)
// Typically this is called by the object conforming to the
// UIViewControllerAnimatedTransitioning protocol that was vended by the transitioning
// delegate.  For purely interactive transitions it should be called by the
// interaction controller. This method effectively updates internal view
// controller state at the end of the transition.
- (void)completeTransition:(BOOL)didComplete;//完成轉換，必須在動畫完成時調用


// Currently only two keys are defined by the
// system - UITransitionContextToViewControllerKey, and
// UITransitionContextFromViewControllerKey. 
// Animators should not directly manipulate a view controller's views and should
// use viewForKey: to get views instead.
- (nullable __kindof UIViewController *)viewControllerForKey:(NSString *)key;//取得視圖控制器

// Currently only two keys are defined by the system -
// UITransitionContextFromViewKey, and UITransitionContextToViewKey
// viewForKey: may return nil which would indicate that the animator should not
// manipulate the associated view controller's view.
- (nullable __kindof UIView *)viewForKey:(NSString *)key NS_AVAILABLE_IOS(8_0);//取得視圖控制器的view，相容iOS7，可以直接用上面取到的viewController.view

創建一個實現UIViewControllerAnimatedTransitioning協議的對象PopAnimation，重要代碼如下：

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

- (void)animateTransition:(id <UIViewControllerContextTransitioning>)transitionContext {
    _transitionContext = transitionContext;

    //當前控制器
    UIViewController *fromViewController = [transitionContext viewControllerForKey:UITransitionContextFromViewControllerKey];
    
    //動畫結束顯示的控制器
    UIViewController *toViewController = [transitionContext viewControllerForKey:UITransitionContextToViewControllerKey];
    
    //執行交互動畫的容器view
    UIView *containerView = [transitionContext containerView];
    [containerView insertSubview:toViewController.view belowSubview:fromViewController.view];
    
    NSTimeInterval duration = [self transitionDuration:transitionContext];
    
    switch (_popAnimationType) {
        case PopAnimationTranslation: {
            CGFloat containerWidth = containerView.frame.size.width;
            toViewController.view.transform = CGAffineTransformMakeTranslation(-containerWidth / 4.0, 0);

            [UIView animateWithDuration:duration animations:^{
                toViewController.view.transform = CGAffineTransformMakeTranslation(0, 0);
                fromViewController.view.transform = CGAffineTransformMakeTranslation(containerWidth, 0);
            }completion:^(BOOL finished) {
                //動畫結束，必須調用此方法
                [transitionContext completeTransition:!transitionContext.transitionWasCancelled];
            }];

            break;
        }
        case PopAnimationFlip: {
            [UIView beginAnimations:@"View Flip" context:nil];
            [UIView setAnimationDuration:duration];
            [UIView setAnimationDelegate:self];
            [UIView setAnimationTransition:UIViewAnimationTransitionFlipFromLeft forView:containerView cache:YES];
            [UIView setAnimationDidStopSelector:@selector(animationDidStop:finished:)];
            [UIView commitAnimations];
            [containerView exchangeSubviewAtIndex:0 withSubviewAtIndex:1];

            break;
        }
        case PopAnimationCube: {
            CATransition *transiton = [CATransition animation];
            transiton.type = @"cube";
            transiton.subtype = @"fromLeft";
            transiton.duration = duration;
            transiton.removedOnCompletion = NO;
            transiton.fillMode = kCAFillModeForwards;
            transiton.delegate = self;
            [containerView.layer addAnimation:transiton forKey:nil];
            [containerView exchangeSubviewAtIndex:0 withSubviewAtIndex:1];

            break;
        }
    }
}

- (void)animationDidStop:(CATransition *)anim finished:(BOOL)flag {
    [_transitionContext completeTransition:!_transitionContext.transitionWasCancelled];
}

剩下的工作：

在上一篇的基礎上，修改UINavigationController的base_pushViewController方法

- (void)base_pushViewController:(UIViewController *)viewController animated:(BOOL)animated
{
    if (![self.interactivePopGestureRecognizer.view.gestureRecognizers containsObject:self.base_panGestureRecognizer]) {
        [self.interactivePopGestureRecognizer.view addGestureRecognizer:self.base_panGestureRecognizer];
        
        self.base_panGestureRecognizer.delegate = [self base_panGestureRecognizerDelegateObject];
        
        self.base_currentDelegateObject = [[NavigationControllerDelegateObject alloc] initWithUINavigationController:self];
        
        [self.base_panGestureRecognizer addTarget:self.base_currentDelegateObject action:@selector(handlePopGestureOperation:)];
        
        self.interactivePopGestureRecognizer.enabled = NO;
    }
    
    [self base_setupViewControllerBasedNavigationBarAppearanceIfNeeded:viewController];
    
    if (![self.viewControllers containsObject:viewController]) {
        [self base_pushViewController:viewController animated:animated];
    }
}

可以看到，去除了私有變數和方法的調用，自定義了名為NavigationControllerDelegateObject的對象，其實現了UINavigationControllerDelegate協議，並實現了pan手勢的處理方法。在此，我暴露了該屬性對象，考慮到以後可能會增加或者修改UINavigationControllerDelegate的實現協議，可以為該對象增加分類來達到目的；還有一個目的，便於修改popAnimation的動畫類型和執行時間。

總結：

兩篇記錄，從不同的方向，記錄了右滑返回手勢功能的實現。利用系統變數和方法，方便快捷；利用協議方法，高度自定義。

但是，利用協議方法，需要處理的方面比較多。雖然上述已經記錄了實現核心，示例代碼中也有詳細代碼，但是仍然還有很多方面未考慮。

目前，我發現的一些問題：

1.導航欄交互效果也需要自行實現，暫未實現原生效果

2.導航欄由隱藏到顯示的效果，有時會出現異常

3.如果帶有bottomBar，效果不理想

如果有好的解決辦法，希望告知，謝謝。

base項目已更新：[email protected]:ALongWay/base.git
項目增加了新的UINavigationController+PopOperation分類，但是未引用到項目中，需要的同學，可先刪除PopGesture分類的引用，再添加該分類的應用。