前言

之前写的GKPageScrollView已经收获接近900个star，最近有时间对里面的GKPageSmoothView进行了优化升级，顺便实现了豆瓣电影详情页的效果，本文主要对GKPageSmoothView的实现做下简单介绍

先看下豆瓣电影的效果图

豆瓣电影详情页

介绍

GKPageSmoothView与GKPageScrollView的实现原理不同
GKPageSmoothView主要是通过修改listScrollView的contentInset，然后添加headerView，并在滑动到一定程度的时候对headerView进行位置和布局的转换
GKPageScrollView主要是包含mainTableView和listScrollView，并在合适的位置处理滑动冲突

GKPageSmoothView支持以下功能：

• 支持上下滑动、左右滑动、手势返回等
• 支持顶部悬停、底部悬停
• 支持底部悬停拖拽，可实现豆瓣电影详情页效果
• 支持如JXCategoryView,JXSegmentedView等的分段控件
• 可实现导航栏颜色渐变、头图下拉放大等效果
• 支持主页下拉刷新、列表页上拉加载

实现

基本原理可以看这里UIScrollView嵌套滚动完美解决方案：仿淘宝、转转首页
下面主要讲讲底部悬停及底部拖拽的实现

底部悬停

底部悬停的实现跟顶部悬停的实现基本一样，前提是headerView的高度要高于屏幕的高度，这样当headerView下滑到可以悬浮的位置时将segmentedView添加到GKPageSmoothView上固定，不再跟随listScrollView滑动，下面看下主要代码

// 滑动到临界位置，固定segmentedView
 if (contentOffsetY < (self.headerContainerHeight - self.frame.size.height)) {
     self.hoverType = GKPageSmoothHoverTypeBottom;
     if (self.segmentedView.superview != self.bottomContainerView) {
           self.bottomContainerView.hidden = NO;
           CGRect frame = self.segmentedView.frame;
           frame.origin.y = 0;
           self.segmentedView.frame = frame;
            [self.bottomContainerView addSubview:self.segmentedView];
      }
}else {
      // 超过临界位置，segmentedView跟listScrollView一起滑动
      if (self.segmentedView.superview != self.headerContainerView) {
            self.bottomContainerView.hidden = YES;
            CGRect frame = self.segmentedView.frame;
            frame.origin.y = self.headerHeight;
            self.segmentedView.frame = frame;
            [self.headerContainerView addSubview:self.segmentedView];
      }
}

底部拖拽

通过观察豆瓣详情页发现，拖拽底部时segmentedView和listScrollView是一起滑动的，所以添加了bottomContainerView来处理，并添加拖拽手势，当拖拽bottomContainerView时，让headerContainerView保持固定不动，segmentedView和listScrollView根据bottomContainerView一起滑动，此时只需处理拖拽手势和listScrollView的滑动即可

1、开始拖拽时，处理headerContainerView和listCollectionView

// 将headerContainerView添加到self
    if (self.headerContainerView.superview != self) {
        CGRect frame = self.headerContainerView.frame;
        frame.origin.y = -(self.currentListScrollView.contentOffset.y + self.headerContainerHeight);
        self.headerContainerView.frame = frame;
        [self insertSubview:self.headerContainerView belowSubview:self.bottomContainerView];
    }
    
    // 将listCollectionView添加到bottomContainerView
    if (self.listCollectionView.superview != self.bottomContainerView) {
        CGRect frame = self.listCollectionView.frame;
        frame.origin.y = self.segmentedHeight;
        frame.size.height = self.bottomContainerView.frame.size.height - self.segmentedHeight;
        self.listCollectionView.frame = frame;
        [self.bottomContainerView addSubview:self.listCollectionView];
        self->_listCollectionView.headerContainerView = nil;
        
        // 记录当前列表的滑动位置
        self.currentListPanBeganContentOffsetY = self.currentListScrollView.contentOffset.y;
        
        for (id<GKPageSmoothListViewDelegate> list in self.listDict.allValues) {
            list.listScrollView.contentInset = UIEdgeInsetsZero;
            list.listScrollView.contentOffset = CGPointZero;
            
            CGRect frame = list.listView.frame;
            frame.size = self.listCollectionView.bounds.size;
            list.listView.frame = frame;
        }
    }

2、结束拖拽时，如果没有到达顶部，恢复到初始位置

    // headerContainerView添加到listHeader
    UIView *listHeader = [self listHeaderForListScrollView:self.currentListScrollView];
    if (self.headerContainerView.superview != listHeader) {
        CGRect frame = self.headerContainerView.frame;
        frame.origin.y = 0;
        self.headerContainerView.frame = frame;
        [listHeader addSubview:self.headerContainerView];
    }
    
    // listCollectionView添加到self
    if (self.listCollectionView.superview != self) {
        self.listCollectionView.frame = self.bounds;
        [self insertSubview:self.listCollectionView belowSubview:self.bottomContainerView];
        self->_listCollectionView.headerContainerView = self.headerContainerView;
        
        for (id<GKPageSmoothListViewDelegate> list in self.listDict.allValues) {
            list.listScrollView.contentInset = UIEdgeInsetsMake(self.headerContainerHeight, 0, 0, 0);
            list.listScrollView.contentOffset = CGPointZero;
            
            CGRect frame = list.listView.frame;
            frame.size = self.listCollectionView.bounds.size;
            list.listView.frame = frame;
        }
        self.currentListScrollView.contentOffset = CGPointMake(0, self.currentListPanBeganContentOffsetY);
    }

3、拖拽滑动处理

- (void)handlePanGesture:(UIPanGestureRecognizer *)panGesture {
    // 
    if (panGesture.state == UIGestureRecognizerStateBegan) {
        [self dragBegan];
    }
    
    CGPoint translation = [panGesture translationInView:self.bottomContainerView];
    if (self.isDragScrollView) {
        [self allowScrolling:self.scrollView];
        // 当UIScrollView在最顶部时，处理视图的滑动
        if (self.scrollView.contentOffset.y <= 0) {
            if (translation.y > 0) { // 向下拖拽
                [self forbidScrolling:self.scrollView];
                self.isDragScrollView = NO;
                
                CGRect frame = self.bottomContainerView.frame;
                frame.origin.y += translation.y;
                self.bottomContainerView.frame = frame;
                
                if (!self.isAllowDragScroll) {
                    self.scrollView.panGestureRecognizer.enabled = NO;
                    self.scrollView.panGestureRecognizer.enabled = YES;
                }
            }
        }
    }else {
        // 根据listScrollView的位置处理bottomContainerView的frame
        CGFloat offsetY = self.scrollView.contentOffset.y;
        CGFloat ceilPointY = self.ceilPointHeight;
        
        if (offsetY <= 0) {
            [self forbidScrolling:self.scrollView];
            if (translation.y > 0) { // 向下拖拽
                CGRect frame = self.bottomContainerView.frame;
                frame.origin.y += translation.y;
                self.bottomContainerView.frame = frame;
            }else if (translation.y < 0 && self.bottomContainerView.frame.origin.y > ceilPointY) { // 向上拖拽
                CGRect frame = self.bottomContainerView.frame;
                frame.origin.y = MAX((self.bottomContainerView.frame.origin.y + translation.y), ceilPointY);
                self.bottomContainerView.frame = frame;
            }
        }else {
            if (translation.y < 0 && self.bottomContainerView.frame.origin.y > ceilPointY) {
                CGRect frame = self.bottomContainerView.frame;
                frame.origin.y = MAX((self.bottomContainerView.frame.origin.y + translation.y), ceilPointY);
                self.bottomContainerView.frame = frame;
            }
            
            if (self.bottomContainerView.frame.origin.y > ceilPointY) {
                [self forbidScrolling:self.scrollView];
            }else {
                [self allowScrolling:self.scrollView];
            }
        }
    }
    
    // 拖拽结束，判断上滑还是下滑并确定是滑动到顶部还是底部
    if (panGesture.state == UIGestureRecognizerStateEnded) {
        CGPoint velocity = [panGesture velocityInView:self.bottomContainerView];
        if (velocity.y < 0) { // 上滑
            if (fabs(self.lastTransitionY) > 5 && self.isDragScrollView == NO) {
                [self dragShowing];
            }else {
                if (self.bottomContainerView.frame.origin.y > (self.ceilPointHeight + self.bottomContainerView.frame.size.height / 2)) {
                    [self dragDismiss];
                }else {
                    [self dragShowing];
                }
            }
        }else { // 下滑
            if (fabs(self.lastTransitionY) > 5 && self.isDragScrollView == NO && !self.scrollView.isDecelerating) {
                [self dragDismiss];
            }else {
                if (self.bottomContainerView.frame.origin.y > (self.ceilPointHeight + self.bottomContainerView.frame.size.height / 2)) {
                    [self dragDismiss];
                }else {
                    [self dragShowing];
                }
            }
        }
        
        [self allowScrolling:self.scrollView];
        self.isDragScrollView = NO;
        self.scrollView = nil;
    }
    
    [panGesture setTranslation:CGPointZero inView:self.bottomContainerView];
    self.lastTransitionY = translation.y;
}

底部拖拽实现基本就这些了，当然还有很多细节，想了解的可以查看具体代码。

使用

1、初始化GKPageSmoothView

self.smoothView = [[GKPageSmoothView alloc] initWithDataSource:self];
[self.view addSubView:self.smoothView];

2、初始化headerView和segmentedView

self.headerView = [UIView new];
self.segmentedView = [JXCategoryView new];

实现GKPageSmoothViewDataSource代理方法

#pragma mark - GKPageSmoothViewDataSource
- (UIView *)headerViewInSmoothView:(GKPageSmoothView *)smoothView {
    return self.headerView;
}

- (UIView *)segmentedViewInSmoothView:(GKPageSmoothView *)smoothView {
    return self.segmentedView;
}

- (NSInteger)numberOfListsInSmoothView:(GKPageSmoothView *)smoothView {
    return 2;
}

- (id<GKPageSmoothListViewDelegate>)smoothView:(GKPageSmoothView *)smoothView initListAtIndex:(NSInteger)index {
    GKDBListView *listView = [GKDBListView new];
    return listView;
}

列表实现GKPageSmoothListViewDelegate代理方法

#pragma mark - GKPageSmoothListViewDelegate
- (UIScrollView *)listScrollView {
    return self.tableView;
}

- (UIView *)listView {
    return self;
}

其他常用属性

顶部临界高度

self.smoothView.ceilPointHeight = NAVBAR_HEIGHT;

开启底部悬浮

self.smoothView.bottomHover = YES;

允许底部拖拽

self.smoothView.allowDragBottom = YES;

delegate常用方法代理

self.smoothView.delegate = self;

/// 列表容器滑动代理
/// @param smoothView smoothView
/// @param scrollView containerScrollView
- (void)smoothView:(GKPageSmoothView *)smoothView scrollViewDidScroll:(UIScrollView *)scrollView;

/// 当前列表滑动代理
/// @param smoothView smoothView
/// @param scrollView 当前的列表scrollView
/// @param contentOffset 转换后的contentOffset
- (void)smoothView:(GKPageSmoothView *)smoothView listScrollViewDidScroll:(UIScrollView *)scrollView contentOffset:(CGPoint)contentOffset;

/// 开始拖拽代理
/// @param smoothView smoothView
- (void)smoothViewDragBegan:(GKPageSmoothView *)smoothView;

/// 结束拖拽代理
/// @param smoothView smoothView
/// @param isOnTop 是否通过拖拽滑动到顶部
- (void)smoothViewDragEnded:(GKPageSmoothView *)smoothView isOnTop:(BOOL)isOnTop;

结语

至此，GKPageSmoothView的介绍已经完成，如果你想了解更多可以查看源码GKPageSmoothView，如果您觉得还不错，可以点个star，您的支持是我最大的动力。

参考

UIScrollView嵌套滚动完美解决方案：仿淘宝、转转首页
iOS仿抖音—评论视图滑动消失