iOS - 在关闭和滚动手势之间切换

我正在尝试模仿 Line 通讯应用程序（日本事实上的通讯应用程序）中的一种行为。

基本上，它们有一个模态视图控制器，内部有滚动视图。当滚动操作到达其内容的顶部时，视图控制器无缝切换到交互式解除动画。此外，当手势将视图返回到屏幕顶部时，控制权将返回到滚动视图。

这是它的外观 gif。

对于我的一生，我无法弄清楚他们是如何做到的。我尝试了几种不同的方法，但都失败了，我没有主意。有人能指出我正确的方向吗？

EDIT2

需要澄清的是，我想要模拟的行为不仅仅是简单地向下拖动窗口。我可以做到，没问题。

我想知道相同的滚动手势（不抬起手指）如何触发解除转换，然后在视图被拖回原始位置后将控制权转移回滚动视图。

这是我无法弄清楚的部分。

结束编辑2

EDIT1

这是我到目前为止所拥有的。我能够使用滚动视图委托方法添加一个处理常规解雇动画的目标选择器，但它仍然无法按预期工作。

我创建一个UIViewController with a UIWebView作为财产。然后我把它放在一个UINavigationController，这是模态呈现的。

导航控制器使用动画/过渡控制器进行常规交互式解除（可以通过在导航栏上进行手势来完成）。

从这里开始，一切正常，但无法从滚动视图触发解雇。

导航控制器.h

@interface NavigationController : UINavigationController <UIViewControllerTransitioningDelegate>

@property (nonatomic, strong) UIPanGestureRecognizer *gestureRecog;

- (void)handleGesture:(UIPanGestureRecognizer*)gestureRecognizer;

@end

导航控制器.m

#import "NavigationController.h"
#import "AnimationController.h"
#import "TransitionController.h"

@implementation NavigationController {
    AnimationController *_animator;
    TransitionController *_interactor;
}

- (instancetype)init {
    self = [super init];

    self.transitioningDelegate = self;

    _animator = [[AnimationController alloc] init];
    _interactor = [[TransitionController alloc] init];

    return self;
}

- (void)viewDidLoad {
    [super viewDidLoad];

    // Set the gesture recognizer
    self.gestureRecog = [[UIPanGestureRecognizer alloc] initWithTarget:self action:@selector(handleGesture:)];
    [self.view addGestureRecognizer:_gestureRecog];
}

- (id<UIViewControllerInteractiveTransitioning>)interactionControllerForDismissal:(id<UIViewControllerAnimatedTransitioning>)animator {
    if (animator == _animator && _interactor.hasStarted) {
        return _interactor;
    }
    return nil;
}

- (id<UIViewControllerAnimatedTransitioning>)animationControllerForDismissedController:(UIViewController *)dismissed {
    if (dismissed == self || [self.viewControllers indexOfObject:dismissed] != NSNotFound) {
        return _animator;
    }
    return nil;
}

- (void)handleGesture:(UIPanGestureRecognizer *)gestureRecog {
    CGFloat threshold = 0.3f;

    CGPoint translation = [gestureRecog translationInView:self.view];
    CGFloat verticalMovement = translation.y / self.view.bounds.size.height;
    CGFloat downwardMovement = fmaxf(verticalMovement, 0.0f);
    CGFloat downwardMovementPercent = fminf(downwardMovement, 1.0f);

    switch (gestureRecog.state) {
        case UIGestureRecognizerStateBegan: {
            _interactor.hasStarted = YES;
            [self dismissViewControllerAnimated:YES completion:nil];
            break;
        }
        case UIGestureRecognizerStateChanged: {
            if (!_interactor.hasStarted) {
                _interactor.hasStarted = YES;
                [self dismissViewControllerAnimated:YES completion:nil];
            }
            _interactor.shouldFinish = downwardMovementPercent > threshold;
            [_interactor updateInteractiveTransition:downwardMovementPercent];
            break;
        }
        case UIGestureRecognizerStateCancelled: {
            _interactor.hasStarted = NO;
            [_interactor cancelInteractiveTransition];
            break;
        }
        case UIGestureRecognizerStateEnded: {
            _interactor.hasStarted = NO;
            if (_interactor.shouldFinish) {
                [_interactor finishInteractiveTransition];
            } else {
                [_interactor cancelInteractiveTransition];
            }
            break;
        }
        default: {
            break;
        }
    }
}

@end

现在，我必须在滚动视图到达顶部时触发手势处理。所以，这就是我在视图控制器中所做的。

WebViewController.m

#import "WebViewController.h"
#import "NavigationController.h"

@interface WebViewController ()

@property (weak, nonatomic) IBOutlet UIWebView *webView;
@end

@implementation WebViewController {
    BOOL _isHandlingPan;
    CGPoint _topContentOffset;
}

- (void)viewDidLoad {
    [super viewDidLoad];

    [self.webView.scrollView setDelegate:self];
}    

- (void)scrollViewDidScroll:(UIScrollView *)scrollView {
    if ((scrollView.panGestureRecognizer.state == UIGestureRecognizerStateBegan ||
         scrollView.panGestureRecognizer.state == UIGestureRecognizerStateChanged) &&
        ! _isHandlingPan &&
        scrollView.contentOffset.y < self.navigationController.navigationBar.translucent ? -64.0f : 0) {

        NSLog(@"Adding scroll target");

        _topContentOffset = CGPointMake(scrollView.contentOffset.x, self.navigationController.navigationBar.translucent ? -64.0f : 0);
        _isHandlingPan = YES;
        [scrollView.panGestureRecognizer addTarget:self action:@selector(handleGesture:)];
    }
}
- (void)scrollViewDidEndDragging:(UIScrollView *)scrollView willDecelerate:(BOOL)decelerate {
    NSLog(@"Did End Dragging");
    if (_isHandlingPan) {
        NSLog(@"Removing action");
        _isHandlingPan = NO;
        [scrollView.panGestureRecognizer removeTarget:self action:@selector(handleGesture:)];
    }
}
- (void)handleGesture:(UIPanGestureRecognizer*)gestureRecognizer {
    [(NavigationController*)self.navigationController handleGesture:gestureRecognizer];
}

这仍然不太正常。即使在关闭动画期间，滚动视图仍然随着手势滚动。

结束编辑1

这是一个自定义的交互式过渡。

首先，你需要设置transitioningDelegate of UIViewController

id<UIViewControllerTransitioningDelegate> transitioningDelegate;

然后实现这两个方法

 //Asks your delegate for the transition animator object to use when dismissing a view controller.
 - animationControllerForDismissedController:
 //Asks your delegate for the interactive animator object to use when dismissing a view controller.
 - interactionControllerForDismissal:

当拖动到顶部时，您开始过渡，您可以使用UIPercentDrivenInteractiveTransition控制滚动过程中的进度。

也可以参考源码ZFDragableModalTransition https://github.com/zoonooz/ZFDragableModalTransition

ZFDragableModalTransition 的图像