App开发流程之右滑返回手势功能续

上一篇记录了利用系统私有变量和方法实现右滑返回手势功能：http://www.cnblogs.com/ALongWay/p/5893515.html

这篇继续记录另一种方案：利用UINavigationController的delegate方法。

核心代理方法有如下两个：

- (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);

第一个代理方法，要求在视图控制器变换时候，返回一个实现UIViewControllerInteractiveTransitioning协议的对象，该对象用于控制交互进度和状态。

UIKit.h/UIViewControllerTransitioning.h中已经准备好了一个这样的对象，名为UIPercentDrivenInteractiveTransition。

主要关注其如下三个方法：

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

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

- (void)finishInteractiveTransition;//完成交互

可以在一个实现了代理方法的类中，定义一个手势目标方法来调用上述方法，达到控制作为变量的UIPercentDrivenInteractiveTransition对象的目的。

主要代码如下：

- (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{
    //将手指在屏幕上的移动距离与屏幕宽度比例作为动画的进度
    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) {
        //新建手势交互对象
        _interactivePopTransition = [[UIPercentDrivenInteractiveTransition alloc] init];

        //开始执行pop动画
        [_naviController popViewControllerAnimated:YES];
    }else if (recognizer.state == UIGestureRecognizerStateChanged) {
         //更新进度
        [_interactivePopTransition updateInteractiveTransition:progress];
    }else if (recognizer.state == UIGestureRecognizerStateEnded
              || recognizer.state == UIGestureRecognizerStateCancelled) {
        //手势结束时如果进度大于一半，那么就完成pop操作，否则取消
        if (progress > 0.5) {
            [_interactivePopTransition finishInteractiveTransition];
        }else {
            [_interactivePopTransition cancelInteractiveTransition];
        }
        
        //手势交互结束，清理对象
        _interactivePopTransition = nil;
    }
}

第二个代理方法，要求在操作开始时候，返回一个实现UIViewControllerAnimatedTransitioning协议的对象，该对象实现了动画内容和执行时间。

该协议有三个方法：

// 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;

第一个方法返回动画时间；第二个方法，可以得到实现了UIViewControllerContextTransitioning协议的对象；第三个方法可选，如果transitionContext对象调用了completeTransition：方法，该代理方法会被调用。

重点是第二个方法的transitionContext对象，其重要的方法如下：

// The view in which the animated transition should take place.
- (nullable UIView *)containerView;//动画所在的容器view
- (BOOL)transitionWasCancelled;//转换是否取消// 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;//完成转换，必须在动画完成时调用


// 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;//取得视图控制器

// 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);//取得视图控制器的view，兼容iOS7，可以直接用上面取到的viewController.view

创建一个实现UIViewControllerAnimatedTransitioning协议的对象PopAnimation，重要代码如下：

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

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

    //当前控制器
    UIViewController *fromViewController = [transitionContext viewControllerForKey:UITransitionContextFromViewControllerKey];
    
    //动画结束显示的控制器
    UIViewController *toViewController = [transitionContext viewControllerForKey:UITransitionContextToViewControllerKey];
    
    //执行交互动画的容器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) {
                //动画结束，必须调用此方法
                [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：

在上一篇的基础上，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，去除了私有变量和方法的调用，自定义了名为NavigationControllerDelegateObject的对象，其实现了UINavigationControllerDelegate协议，并实现了pan手势的处理方法。在此，我暴露了该属性对象，考虑到以后可能会增加或者修改UINavigationControllerDelegate的实现协议，可以为该对象增加分类来达到目的；还有一个目的，便于修改popAnimation的动画类型和执行时间。

总结：

两篇记录，从不同的方向，记录了右滑返回手势功能的实现。利用系统变量和方法，方便快捷；利用协议方法，高度自定义。

但是，利用协议方法，需要处理的方面比较多。虽然上述已经记录了实现核心，示例代码中也有详细代码，但是仍然还有很多方面未考虑。

目前，我发现的一些问题：

1.导航栏交互效果也需要自行实现，暂未实现原生效果

2.导航栏由隐藏到显示的效果，有时会出现异常

3.如果带有bottomBar，效果不理想

如果有好的解决办法，希望告知，谢谢。

base项目已更新：[email protected]:ALongWay/base.git项目增加了新的UINavigationController+PopOperation分类，但是未引用到项目中，需要的同学，可先删除PopGesture分类的引用，再添加该分类的应用。