iOS 7的手势滑动返回功能

版权声明：本文为博主原创文章，未经博主允许不得转载。

隐藏navigationController的navigationBar后，系统自带的左边侧滑pop手势就消失了。

之前随手写过一篇《使用UIScreenEdgePanGestureRecognizer实现swipe to pop效果》，挺粗糙的。

现在使用默认模板创建的iOS App都支持手势返回功能，如果导航栏的返回按钮是自定义的那么则会失效，也可以参考这里手动设置无效。

 if ([self.navigationController respondsToSelector:@selector(interactivePopGestureRecognizer)]) {
     self.navigationController.interactivePopGestureRecognizer.enabled = NO;
 }

如果是因为自定义导航按钮而导致手势返回失效，那么可以在NavigationController的viewDidLoad函数中添加如下代码：

 - (void)viewDidLoad
 {
     [super viewDidLoad];
     // Do any additional setup after loading the view.

     __weak typeof (self) weakSelf = self;
     if ([self respondsToSelector:@selector(interactivePopGestureRecognizer)]) {
         self.interactivePopGestureRecognizer.delegate = weakSelf;
     }
 }

这样写了以后就可以通过手势滑动返回上一层了，但是如果在push过程中触发手势滑动返回，会导致导航栏崩溃（从日志中可以看出）。针对这个问题，我们需要在pop过程禁用手势滑动返回功能：

 - (void)pushViewController:(UIViewController *)viewController animated:(BOOL)animated
 {
     // fix 'nested pop animation can result in corrupted navigation bar'
     if ([self respondsToSelector:@selector(interactivePopGestureRecognizer)]) {
         self.interactivePopGestureRecognizer.enabled = NO;
     }

     [super pushViewController:viewController animated:animated];
 }

 - (void)navigationController:(UINavigationController *)navigationController
        didShowViewController:(UIViewController *)viewController
                     animated:(BOOL)animated
 {
     if ([navigationController respondsToSelector:@selector(interactivePopGestureRecognizer)]) {
         navigationController.interactivePopGestureRecognizer.enabled = YES;
     }
 }

除了使用系统默认的动画，还可以使用自定义过渡动画（ 丰满的文档）：

 - (id<UIViewControllerAnimatedTransitioning>)navigationController:(UINavigationController *)navigationController
                                   animationControllerForOperation:(UINavigationControllerOperation)operation
                                                fromViewController:(UIViewController *)fromVC
                                                  toViewController:(UIViewController *)toVC
 {
     if (operation == UINavigationControllerOperationPop) {
         if (self.popAnimator == nil) {
             self.popAnimator = [WQPopAnimator new];
         }
         return self.popAnimator;
     }

     return nil;
 }

 - (id<UIViewControllerInteractiveTransitioning>)navigationController:(UINavigationController *)navigationController
                          interactionControllerForAnimationController:(id<UIViewControllerAnimatedTransitioning>)animationController
 {
     return self.popInteractionController;
 }

 #pragma mark -

 - (void)enablePanToPopForNavigationController:(UINavigationController *)navigationController
 {
     UIScreenEdgePanGestureRecognizer *left2rightSwipe = [[UIScreenEdgePanGestureRecognizer alloc]
                                                          initWithTarget:self
                                                          action:@selector(didPanToPop:)];
     //[left2rightSwipe setDelegate:self];
     [left2rightSwipe setEdges:UIRectEdgeLeft];
     [navigationController.view addGestureRecognizer:left2rightSwipe];

     self.popAnimator = [WQPopAnimator new];
     self.supportPan2Pop = YES;
 }

 - (void)didPanToPop:(UIPanGestureRecognizer *)panGesture
 {
     if (!self.supportPan2Pop) return ;

     UIView *view = self.navigationController.view;

     if (panGesture.state == UIGestureRecognizerStateBegan) {
         self.popInteractionController = [UIPercentDrivenInteractiveTransition new];
         [self.navigationController popViewControllerAnimated:YES];
     } else if (panGesture.state == UIGestureRecognizerStateChanged) {
         CGPoint translation = [panGesture translationInView:view];
         CGFloat d = fabs(translation.x / CGRectGetWidth(view.bounds));
         [self.popInteractionController updateInteractiveTransition:d];
     } else if (panGesture.state == UIGestureRecognizerStateEnded) {
         if ([panGesture velocityInView:view].x > 0) {
             [self.popInteractionController finishInteractiveTransition];
         } else {
             [self.popInteractionController cancelInteractiveTransition];
         }
         self.popInteractionController = nil;
     }
 }

如下这个代理方法是用来提供一个非交互式的过渡动画的：

 - (id<UIViewControllerAnimatedTransitioning>)navigationController:(UINavigationController *)navigationController
                                   animationControllerForOperation:(UINavigationControllerOperation)operation
                                                fromViewController:(UIViewController *)fromVC
                                                  toViewController:(UIViewController *)toVC
 {
     if (operation == UINavigationControllerOperationPop) {
         if (self.popAnimator == nil) {
             self.popAnimator = [WQPopAnimator new];
         }
         return self.popAnimator;
     }

     return nil;
 }

而下面这个代理方法则是提供交互式动画：

 - (id<UIViewControllerInteractiveTransitioning>)navigationController:(UINavigationController *)navigationController
                          interactionControllerForAnimationController:(id<UIViewControllerAnimatedTransitioning>)animationController
 {
     return self.popInteractionController;
 }

这两个组合起来使用。首先，我们需要有个动画：

 @interface WQPopAnimator : NSObject <UIViewControllerAnimatedTransitioning>

 @end

 #import "WQPopAnimator.h"

 @implementation WQPopAnimator

 - (NSTimeInterval)transitionDuration:(id <UIViewControllerContextTransitioning>)transitionContext
 {
     return 0.4;
 }

 - (void)animateTransition:(id<UIViewControllerContextTransitioning>)transitionContext
 {
     UIViewController *toViewController = [transitionContext viewControllerForKey:UITransitionContextToViewControllerKey];
     UIViewController *fromViewController = [transitionContext viewControllerForKey:UITransitionContextFromViewControllerKey];
     [[transitionContext containerView] insertSubview:toViewController.view belowSubview:fromViewController.view];

     __block CGRect toRect = toViewController.view.frame;
     CGFloat originX = toRect.origin.x;
     toRect.origin.x -= toRect.size.width / 3;
     toViewController.view.frame = toRect;

     [UIView animateWithDuration:[self transitionDuration:transitionContext] animations:^{
         CGRect fromRect = fromViewController.view.frame;
         fromRect.origin.x += fromRect.size.width;
         fromViewController.view.frame = fromRect;

         toRect.origin.x = originX;
         toViewController.view.frame = toRect;
     } completion:^(BOOL finished) {
         [transitionContext completeTransition:![transitionContext transitionWasCancelled]];
     }];
 }

 @end

其次，交互式动画是通过

 UIPercentDrivenInteractiveTransition

来维护的，在滑动过程中根据滑动距离来进行更新：

 } else if (panGesture.state == UIGestureRecognizerStateChanged) {
         CGPoint translation = [panGesture translationInView:view];
         CGFloat d = fabs(translation.x / CGRectGetWidth(view.bounds));
         [self.popInteractionController updateInteractiveTransition:d];

当手势结束时要做出收尾动作：

 } else if (panGesture.state == UIGestureRecognizerStateEnded) {
         if ([panGesture velocityInView:view].x > 0) {
             [self.popInteractionController finishInteractiveTransition];
         } else {
             [self.popInteractionController cancelInteractiveTransition];
         }
         self.popInteractionController = nil;
     }

同样地，自定义的动画也会有上面提到的导航栏崩溃问题，也可以通过类似的方法来解决：

 - (void)navigationController:(UINavigationController *)navigationController
        didShowViewController:(UIViewController *)viewController
                     animated:(BOOL)animated
 {
     if (viewController == self.navigationController.pushingViewController) {
         self.supportPan2Pop = YES;
         self.navigationController.pushingViewController = nil;
     }

补充：位于当前navgationController的第一个（[0]）viewController时需要设置手势代理，不响应。