再谈iOS 7的手势滑动返回功能

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。