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;
}

End