再谈iOS 7的手势滑动返回功能

本文转载至 http://blog.csdn.net/jasonblog/article/details/28282147 

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。

1. if ([self.navigationController respondsToSelector:@selector(interactivePopGestureRecognizer)]) {
2. self.navigationController.interactivePopGestureRecognizer.enabled = NO;
3. }

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：

1. - (void)viewDidLoad
2. {
3. [super viewDidLoad];
4. // Do any additional setup after loading the view.
5. __weak typeof (self) weakSelf = self;
6. if ([self respondsToSelector:@selector(interactivePopGestureRecognizer)]) {
7. self.interactivePopGestureRecognizer.delegate = weakSelf;
8. }
9. }

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：

1. - (void)pushViewController:(UIViewController *)viewController animated:(BOOL)animated
2. {
3. // fix 'nested pop animation can result in corrupted navigation bar'
4. if ([self respondsToSelector:@selector(interactivePopGestureRecognizer)]) {
5. self.interactivePopGestureRecognizer.enabled = NO;
6. }
7. [super pushViewController:viewController animated:animated];
8. }

1. - (void)navigationController:(UINavigationController *)navigationController
2. didShowViewController:(UIViewController *)viewController
3. animated:(BOOL)animated
4. {
5. if ([navigationController respondsToSelector:@selector(interactivePopGestureRecognizer)]) {
6. navigationController.interactivePopGestureRecognizer.enabled = YES;
7. }
8. }

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）：

1. - (id<UIViewControllerAnimatedTransitioning>)navigationController:(UINavigationController *)navigationController
2. animationControllerForOperation:(UINavigationControllerOperation)operation
3. fromViewController:(UIViewController *)fromVC
4. toViewController:(UIViewController *)toVC
5. {
6. if (operation == UINavigationControllerOperationPop) {
7. if (self.popAnimator == nil) {
8. self.popAnimator = [WQPopAnimator new];
9. }
10. return self.popAnimator;
11. }
12. return nil;
13. }
14. - (id<UIViewControllerInteractiveTransitioning>)navigationController:(UINavigationController *)navigationController
15. interactionControllerForAnimationController:(id<UIViewControllerAnimatedTransitioning>)animationController
16. {
17. return self.popInteractionController;
18. }
19. #pragma mark -
20. - (void)enablePanToPopForNavigationController:(UINavigationController *)navigationController
21. {
22. UIScreenEdgePanGestureRecognizer *left2rightSwipe = [[UIScreenEdgePanGestureRecognizer alloc]
23. initWithTarget:self
24. action:@selector(didPanToPop:)];
25. //[left2rightSwipe setDelegate:self];
26. [left2rightSwipe setEdges:UIRectEdgeLeft];
27. [navigationController.view addGestureRecognizer:left2rightSwipe];
28. self.popAnimator = [WQPopAnimator new];
29. self.supportPan2Pop = YES;
30. }
31. - (void)didPanToPop:(UIPanGestureRecognizer *)panGesture
32. {
33. if (!self.supportPan2Pop) return ;
34. UIView *view = self.navigationController.view;
35. if (panGesture.state == UIGestureRecognizerStateBegan) {
36. self.popInteractionController = [UIPercentDrivenInteractiveTransition new];
37. [self.navigationController popViewControllerAnimated:YES];
38. } else if (panGesture.state == UIGestureRecognizerStateChanged) {
39. CGPoint translation = [panGesture translationInView:view];
40. CGFloat d = fabs(translation.x / CGRectGetWidth(view.bounds));
41. [self.popInteractionController updateInteractiveTransition:d];
42. } else if (panGesture.state == UIGestureRecognizerStateEnded) {
43. if ([panGesture velocityInView:view].x > 0) {
44. [self.popInteractionController finishInteractiveTransition];
45. } else {
46. [self.popInteractionController cancelInteractiveTransition];
47. }
48. self.popInteractionController = nil;
49. }
50. }

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：

1. - (id<UIViewControllerAnimatedTransitioning>)navigationController:(UINavigationController *)navigationController
2. animationControllerForOperation:(UINavigationControllerOperation)operation
3. fromViewController:(UIViewController *)fromVC
4. toViewController:(UIViewController *)toVC
5. {
6. if (operation == UINavigationControllerOperationPop) {
7. if (self.popAnimator == nil) {
8. self.popAnimator = [WQPopAnimator new];
9. }
10. return self.popAnimator;
11. }
12. return nil;
13. }

而下面这个代理方法则是提供交互式动画：

1. - (id<UIViewControllerInteractiveTransitioning>)navigationController:(UINavigationController *)navigationController
2. interactionControllerForAnimationController:(id<UIViewControllerAnimatedTransitioning>)animationController
3. {
4. return self.popInteractionController;
5. }

这两个组合起来使用。首先，我们需要有个动画：

1. @interface WQPopAnimator : NSObject <UIViewControllerAnimatedTransitioning>
2. @end

1. #import "WQPopAnimator.h"
2. @implementation WQPopAnimator
3. - (NSTimeInterval)transitionDuration:(id <UIViewControllerContextTransitioning>)transitionContext
4. {
5. return 0.4;
6. }
7. - (void)animateTransition:(id<UIViewControllerContextTransitioning>)transitionContext
8. {
9. UIViewController *toViewController = [transitionContext viewControllerForKey:UITransitionContextToViewControllerKey];
10. UIViewController *fromViewController = [transitionContext viewControllerForKey:UITransitionContextFromViewControllerKey];
11. [[transitionContext containerView] insertSubview:toViewController.view belowSubview:fromViewController.view];
12. __block CGRect toRect = toViewController.view.frame;
13. CGFloat originX = toRect.origin.x;
14. toRect.origin.x -= toRect.size.width / 3;
15. toViewController.view.frame = toRect;
16. [UIView animateWithDuration:[self transitionDuration:transitionContext] animations:^{
17. CGRect fromRect = fromViewController.view.frame;
18. fromRect.origin.x += fromRect.size.width;
19. fromViewController.view.frame = fromRect;
20. toRect.origin.x = originX;
21. toViewController.view.frame = toRect;
22. } completion:^(BOOL finished) {
23. [transitionContext completeTransition:![transitionContext transitionWasCancelled]];
24. }];
25. }
26. @end

其次，交互式动画是通过

1. UIPercentDrivenInteractiveTransition

来维护的，在滑动过程中根据滑动距离来进行更新：

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

当手势结束时要做出收尾动作：

1. } else if (panGesture.state == UIGestureRecognizerStateEnded) {
2. if ([panGesture velocityInView:view].x > 0) {
3. [self.popInteractionController finishInteractiveTransition];
4. } else {
5. [self.popInteractionController cancelInteractiveTransition];
6. }
7. self.popInteractionController = nil;
8. }

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：

1. - (void)navigationController:(UINavigationController *)navigationController
2. didShowViewController:(UIViewController *)viewController
3. animated:(BOOL)animated
4. {
5. if (viewController == self.navigationController.pushingViewController) {
6. self.supportPan2Pop = YES;
7. self.navigationController.pushingViewController = nil;
8. }

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。