FDFullscreenPopGesture阅读

首先贴上sunnyxx大神的博客 一个丝滑的全屏滑动返回手势

FDFullscreenPopGesture是通过替换系统原生的右滑返回手势来实现全屏滑动返回的效果

手势返回

为了实现对原有项目0侵入性，那么就需要hook原有方法来实现

+ (void)load
{
    // Inject "-pushViewController:animated:"
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        Class class = [self class];
        
        SEL originalSelector = @selector(pushViewController:animated:);
        SEL swizzledSelector = @selector(fd_pushViewController:animated:);
        
        Method originalMethod = class_getInstanceMethod(class, originalSelector);
        Method swizzledMethod = class_getInstanceMethod(class, swizzledSelector);
        
        BOOL success = class_addMethod(class, originalSelector, method_getImplementation(swizzledMethod), method_getTypeEncoding(swizzledMethod));
        if (success) {
            class_replaceMethod(class, swizzledSelector, method_getImplementation(originalMethod), method_getTypeEncoding(originalMethod));
        } else {
            method_exchangeImplementations(originalMethod, swizzledMethod);
        }
    });
}

hook这种也不需要详解了，谷歌一下也有很多解释了，最主要的还是要看被hook的fd_pushViewController:animated:方法

- (void)fd_pushViewController:(UIViewController *)viewController animated:(BOOL)animated
{
    if (![self.interactivePopGestureRecognizer.view.gestureRecognizers containsObject:self.fd_fullscreenPopGestureRecognizer]) {
        
        // Add our own gesture recognizer to where the onboard screen edge pan gesture recognizer is attached to.
        [self.interactivePopGestureRecognizer.view addGestureRecognizer:self.fd_fullscreenPopGestureRecognizer];
        
        // Forward the gesture events to the private handler of the onboard gesture recognizer.
        NSArray *internalTargets = [self.interactivePopGestureRecognizer valueForKey:@"targets"];
        id internalTarget = [internalTargets.firstObject valueForKey:@"target"];
        SEL internalAction = NSSelectorFromString(@"handleNavigationTransition:");
        self.fd_fullscreenPopGestureRecognizer.delegate = self.fd_popGestureRecognizerDelegate;
        [self.fd_fullscreenPopGestureRecognizer addTarget:internalTarget action:internalAction];
        
        // Disable the onboard gesture recognizer.
        self.interactivePopGestureRecognizer.enabled = NO;
    }
    
    // Handle perferred navigation bar appearance.
    [self fd_setupViewControllerBasedNavigationBarAppearanceIfNeeded:viewController];
    
    // Forward to primary implementation.
    if (![self.viewControllers containsObject:viewController]) {
        [self fd_pushViewController:viewController animated:animated];
    }
}

第一步的做法是用自己创建的手势来替换掉系统原生的返回手势以实现全屏返回手势

为什么自己创建的fd_fullscreenPopGestureRecognizer的target&action要设为系统默认的target&action呢？因为UINavigationController导航控制器的pop&push的层级关系是由系统管理的(参考[J_雨])。所以只需要决定fd_fullscreenPopGestureRecognizer是否能响应就行了

- (BOOL)gestureRecognizerShouldBegin:(UIPanGestureRecognizer *)gestureRecognizer
{
    // Ignore when no view controller is pushed into the navigation stack.
    if (self.navigationController.viewControllers.count <= 1) {
        return NO;
    }
    
    // Ignore when the active view controller doesn't allow interactive pop.
    UIViewController *topViewController = self.navigationController.viewControllers.lastObject;
    if (topViewController.fd_interactivePopDisabled) {
        return NO;
    }
    
    // Ignore when the beginning location is beyond max allowed initial distance to left edge.
    CGPoint beginningLocation = [gestureRecognizer locationInView:gestureRecognizer.view];
    CGFloat maxAllowedInitialDistance = topViewController.fd_interactivePopMaxAllowedInitialDistanceToLeftEdge;
    if (maxAllowedInitialDistance > 0 && beginningLocation.x > maxAllowedInitialDistance) {
        return NO;
    }

    // Ignore pan gesture when the navigation controller is currently in transition.
    if ([[self.navigationController valueForKey:@"_isTransitioning"] boolValue]) {
        return NO;
    }
    
    // Prevent calling the handler when the gesture begins in an opposite direction.
    CGPoint translation = [gestureRecognizer translationInView:gestureRecognizer.view];
    BOOL isLeftToRight = [UIApplication sharedApplication].userInterfaceLayoutDirection == UIUserInterfaceLayoutDirectionLeftToRight;
    CGFloat multiplier = isLeftToRight ? 1 : - 1;
    if ((translation.x * multiplier) <= 0) {
        return NO;
    }
    
    return YES;
}

当为以下情况的时候，全屏返回手势不生效:

• 导航栈没有push视图控制器，也就是说导航栈只有根视图或则没有视图的时候不生效
• 当前导航栈的栈顶视图控制器不允许全屏返回
• 手势开始的点小于设置的最大允许距离
• 当前正在进行过渡态动画
• 当前手势不是从左往后滑

导航栏的显示隐藏

- (void)fd_setupViewControllerBasedNavigationBarAppearanceIfNeeded:(UIViewController *)appearingViewController
{
    if (!self.fd_viewControllerBasedNavigationBarAppearanceEnabled) {
        return;
    }
    
    __weak typeof(self) weakSelf = self;
    _FDViewControllerWillAppearInjectBlock block = ^(UIViewController *viewController, BOOL animated) {
        __strong typeof(weakSelf) strongSelf = weakSelf;
        if (strongSelf) {
            [strongSelf setNavigationBarHidden:viewController.fd_prefersNavigationBarHidden animated:animated];
        }
    };
    
    // Setup will appear inject block to appearing view controller.
    // Setup disappearing view controller as well, because not every view controller is added into
    // stack by pushing, maybe by "-setViewControllers:".
    appearingViewController.fd_willAppearInjectBlock = block;
    UIViewController *disappearingViewController = self.viewControllers.lastObject;
    if (disappearingViewController && !disappearingViewController.fd_willAppearInjectBlock) {
        disappearingViewController.fd_willAppearInjectBlock = block;
    }
}

每次push一个新的视图控制器的时候，都会设置一个_FDViewControllerWillAppearInjectBlock，用于在视图即将显示的设置导航栏的显示与隐藏，因此我们只需要简单的设置fd_prefersNavigationBarHidden属性，试图控制器每次在即将显示viewWillAppear:的时候设置导航栏是否隐藏就行了。

疑问

- (void)fd_viewWillDisappear:(BOOL)animated
{
    // Forward to primary implementation.
    [self fd_viewWillDisappear:animated];
    
    dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(0 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{
        UIViewController *viewController = self.navigationController.viewControllers.lastObject;
        if (viewController && !viewController.fd_prefersNavigationBarHidden) {
            [self.navigationController setNavigationBarHidden:NO animated:NO];
        }
    });
}

对于这里，我不是很明白为什么在试图控制器即将消失的时候，为什么还要设置导航栏隐藏呢？如果是pop的话，viewController为nil，但如果是push的话，不是已经在viewWillAppear:的时候设置了导航了吗？

个人感觉是最后避免想显示导航栏却没显示的不就措施吧？

希望有懂的大神能告诉我一下，私聊我也行，评论区讲解一下也想，当然有不同的想法的也可以在评论区发表意见