自定义全屏滑动返回手势

UIScreenEdgePanGestureRecognizer : UIPanGestureRecognizer : UIPanGestureRecognizer

专门处理在屏幕边缘触发的手势类型
edges属性叫，来设置它的触发边缘（上、下、左、右、全部）

私有类，看来是专门用来做导航控制器交互动画的

delegate == _UINavigationInteractiveTransition
taget == _UINavigationInteractiveTransition
私有类，专门来做导航控制器交互动画

acrtion == handleNavigationTransition
- UIGestureRecognizer有个叫_targets的属性,数组
  _targets[0] == (action=handleNavigationTransition:, target=<_UINavigationInteractiveTransition 0x7faae8508ea0>)
  是UIGestureRecognizerTarget 私有类

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最简单版，全屏返回手势

/**
 全屏滑动返回
 利用系统 pop返回功能
 */
- (void)viewDidLoad {
    [super viewDidLoad];
    
    // 获取系统自带滑动手势的target对象
    id target = self.interactivePopGestureRecognizer.delegate;
    // 创建全屏滑动手势，调用系统自带滑动手势的target的action方法
    UIPanGestureRecognizer *pan = [[UIPanGestureRecognizer alloc] initWithTarget:target action:@selector(handleNavigationTransition:)];
    // NSSelectorFromString(@"
    // 设置手势代理，拦截手势触发
    pan.delegate = self;
    // 给导航控制器的view添加全屏滑动手势
    [self.view addGestureRecognizer:pan];
    // 禁止使用系统自带的滑动手势
    self.interactivePopGestureRecognizer.enabled = NO;
}

// 是否开始触发。
// 作用：拦截手势触发
- (BOOL)gestureRecognizerShouldBegin:(UIGestureRecognizer *)gestureRecognizer
{
    // 注意：只有非根控制器才有滑动返回功能，根控制器没有。
    // 判断导航控制器是否只有一个子控制器，如果只有一个子控制器，肯定是根控制器
    if (self.childViewControllers.count == 1) {
        // 表示用户在根控制器界面，就不需要触发滑动手势，
        return NO;
    }
    return YES;
}

优点：简单易于理解
缺点：每个控制器不能控制自己的导航栏状态，显示也有问题
- 不能单独设置每个控制器，全屏手势是否生效

UINavigationController+FDFullscreenPopGesture

完美解决上面问题

- (void)fd_viewWillAppear:(BOOL)animated
{
    // 执行原始方法
    [self fd_viewWillAppear:animated];
    
    // 即将要显示时，调用block, 完成每个控制器 导航栏你的显示
    if (self.fd_willAppearInjectBlock) {
        self.fd_willAppearInjectBlock(self, animated);
    }
}
---------------------------------------------------------

- (void)fd_pushViewController:(UIViewController *)viewController animated:(BOOL)animated
{
    if (![self.interactivePopGestureRecognizer.view.gestureRecognizers containsObject:self.fd_fullscreenPopGestureRecognizer]) {
       
        // 添加自定义全屏手势
        [self.interactivePopGestureRecognizer.view addGestureRecognizer:self.fd_fullscreenPopGestureRecognizer];
        
        // 使用系统侧滑返回手势 target 和 处理方法
        NSArray *internalTargets = [self.interactivePopGestureRecognizer valueForKey:@"targets"];
        id internalTarget = [internalTargets.firstObject valueForKey:@"target"];
        // 私有处理方法不能用kvc 获取？？
        SEL internalAction = NSSelectorFromString(@"handleNavigationTransition:");
        // 为手势设置代理
        self.fd_fullscreenPopGestureRecognizer.delegate = self.fd_popGestureRecognizerDelegate;
        // 为手势设置target-action
        [self.fd_fullscreenPopGestureRecognizer addTarget:internalTarget action:internalAction];
        
        // 禁用系统的手势事件
        self.interactivePopGestureRecognizer.enabled = NO;
    }
    
    // 处理所有 push方法 之前都进行操作
    [self fd_setupViewControllerBasedNavigationBarAppearanceIfNeeded:viewController];
    
    // 调用原始方法 进行push, 判断已经有这个子控制器，就不会push
    if (![self.viewControllers containsObject:viewController]) {
        [self fd_pushViewController:viewController animated:animated];
    }
}


/**
 所有push操作，都会来到这个方法
 对导航栏外观 进行预处理
 */
- (void)fd_setupViewControllerBasedNavigationBarAppearanceIfNeeded:(UIViewController *)appearingViewController
{
    // 导航控制器 是否允许 所有导航栏的操作
    // 为NO 各个子控制器不能单独操作
    if (!self.fd_viewControllerBasedNavigationBarAppearanceEnabled) {
        return;
    }
    
    // 创建实现一个block 包含2个参数
    // 进行处理操作
    __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];
        }
    };
    
    // 给即将push进来的控制器 赋值blcok
    // 以后传什么参数, 由它自己决定！
    appearingViewController.fd_willAppearInjectBlock = block;
    // 给即将消失是的控制器 赋值block, 就是当前控制器
    // 有的子控制器不是 push进来的, 本身就是导航控制器的 根控制器
    UIViewController *disappearingViewController = self.viewControllers.lastObject;
    if (disappearingViewController && !disappearingViewController.fd_willAppearInjectBlock) {
        disappearingViewController.fd_willAppearInjectBlock = block;
    }
}

- (_FDFullscreenPopGestureRecognizerDelegate *)fd_popGestureRecognizerDelegate
{
    _FDFullscreenPopGestureRecognizerDelegate *delegate = objc_getAssociatedObject(self, _cmd);
    
    if (!delegate) {
        delegate = [[_FDFullscreenPopGestureRecognizerDelegate alloc] init];
        delegate.navigationController = self;
        
        objc_setAssociatedObject(self, _cmd, delegate, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
    }
    return delegate;
}

/**
 懒加载创建 自定义全屏手势
 */
- (UIPanGestureRecognizer *)fd_fullscreenPopGestureRecognizer
{
    UIPanGestureRecognizer *panGestureRecognizer = objc_getAssociatedObject(self, _cmd);
    
    if (!panGestureRecognizer) {
        panGestureRecognizer = [[UIPanGestureRecognizer alloc] init];
        panGestureRecognizer.maximumNumberOfTouches = 1;
        
        objc_setAssociatedObject(self, _cmd, panGestureRecognizer, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
    }
    return panGestureRecognizer;
}

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