自定义导航栏返回时的滑动手势处理

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];

　　__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：

- (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。