无线循环的滚动视图方案

- (void)collectionView:(UICollectionView *)collectionView didEndDisplayingCell:(UICollectionViewCell *)cell forItemAtIndexPath:(NSIndexPath *)indexPath;

- (nullable UICollectionViewCell *)cellForItemAtIndexPath:(NSIndexPath *)indexPath

- (void)scrollToItemAtIndexPath:(NSIndexPath *)indexPath atScrollPosition:(UICollectionViewScrollPosition)scrollPosition animated:(BOOL)animated;

- (void)tableView:(UITableView *)tableView didEndDisplayingCell:(UITableViewCell *)cell forRowAtIndexPath:(NSIndexPath*)indexPath API_AVAILABLE(ios(6.0));

- (nullable __kindof UITableViewCell *)cellForRowAtIndexPath:(NSIndexPath *)indexPath;   // returns nil if cell is not visible or index path is out of range

- (void)scrollToRowAtIndexPath:(NSIndexPath *)indexPath atScrollPosition:(UITableViewScrollPosition)scrollPosition animated:(BOOL)animated;

- (void)scrollViewDidScroll:(UIScrollView *)scrollView;                                               // any offset changes

// called on finger up if the user dragged. decelerate is true if it will continue moving afterwards
- (void)scrollViewDidEndDragging:(UIScrollView *)scrollView willDecelerate:(BOOL)decelerate;

- (void)scrollViewDidEndDecelerating:(UIScrollView *)scrollView;      // called when scroll view grinds to a halt

CGFloat screenHeigh = self.view.frame.size.height;
NSInteger offsety = scrollView.contentOffset.y;
NSInteger height = screenHeigh;
CGFloat ratio = offsety % height;
NSInteger index = offsety/screenHeigh;
ULLogInfo(@"LIVEMANAGER： scrollViewDidScroll=index=%@",@(index));
if (index == self.currentIndex) {
    return;
}
NSLog(@"enter_live_room_new %s, %@", __PRETTY_FUNCTION__, @"1");

if (scrollView == self.tableView && ratio == 0) {
    self.currentIndex = index;
}

- (void)setContentOffset:(CGPoint)contentOffset animated:(BOOL)animated;  // animate at constant velocity to new offset

- (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView

- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section;

if (self.currentIndex == 0 && !self.isFirstEntry) {
    // 滚动到了第一个位置
}

// 需要滚动到列表的倒数第二个位置
NSInteger rowCount = self.liveListArray.count;
if (rowCount >= 2) {
    self.currentIndex = rowCount-2;
    [self.tableView scrollToRowAtIndexPath:[NSIndexPath indexPathForRow:self.currentIndex inSection:0] atScrollPosition:UITableViewScrollPositionTop animated:NO];
} else {
    // 如果数组的个数小于2 那么证明只有一个直播间不可以滚动
    [self canSlideChangeLiveRoom:NO];
}

if (self.currentIndex == self.liveListArray.count -1) {
    // 滚动到了最后一个
}

// 滚动到最后一个位置 此处的数据为补充数据 需要滚动列表
    // 需要滚到第一个位置
    if (self.liveListArray.count == 1) {
        // 如果当前直播间列表只有一个直播间
        [self canSlideChangeLiveRoom:NO];
    } else {
        self.currentIndex = 1;
        [self.tableView scrollToRowAtIndexPath:[NSIndexPath indexPathForRow:self.currentIndex inSection:0] atScrollPosition:UITableViewScrollPositionTop animated:NO];
    }

- (NSArray *)reCombineWithArray:(NSArray *)liveList {
    NSMutableArray *listArray = [NSMutableArray arrayWithArray:liveList];
    // 当前直播间列表中有多个直播间
    ULDiscovery *firstObject = listArray.firstObject;
    ULDiscovery *firstPlacehoder = [ULDiscovery parse:[firstObject toDictionary]];
    ULDiscovery * lastObject = listArray.lastObject;
    ULDiscovery *lastPlacehoder = [ULDiscovery parse:[lastObject toDictionary]];
    [listArray addObject:firstPlacehoder];
    [listArray insertObject:lastPlacehoder atIndex:0];
    return [listArray copy];
}

///  滚动到下一个直播间的index
/// @param aDiscovery aDiscovery description
/// @param scrollDown scrollDown description
- (NSInteger)findNextLiveItems:(NSArray <ULDiscovery *> *)liveList index:(NSInteger)index destIndex:(NSInteger)destIndex scrollDown:(BOOL)scrollDown {
    if (scrollDown && (destIndex >= self.liveListArray.count - 1)) {
        // 如果是向下滚动且为最后一个直播间向第一个直播间滚动 第一个直播间被拉黑
        // 需要滚动到第一个直播间的下一个直播间
        // 数组正向遍历
        ULDiscovery *destDis = [liveList ul_safeObjectAtIndex:index];
        __block NSInteger disIndex = destIndex;
        [liveList enumerateObjectsUsingBlock:^(ULDiscovery * _Nonnull obj, NSUInteger idx, BOOL * _Nonnull stop) {
            if (obj.room.roomID == destDis.room.roomID) {
                *stop = YES;
                disIndex = idx;
            }
        }];
        destIndex = disIndex+1;
        self.currentIndex = 0;
        self.lastRoomIndex = -1;
    } else if (!scrollDown && destIndex <= 0) {
        // 如果是向上滚动且为第一个直播间向最后一个直播间滚动 最后一个直播间被拉黑
        ULDiscovery *destDis = [liveList ul_safeObjectAtIndex:index];
        __block NSInteger disIndex = destIndex;
        [liveList enumerateObjectsWithOptions:NSEnumerationReverse usingBlock:^(ULDiscovery * _Nonnull obj, NSUInteger idx, BOOL * _Nonnull stop) {
            if (obj.room.roomID == destDis.room.roomID) {
                disIndex = idx;
                *stop = YES;
            }
        }];
        destIndex = disIndex-1;
        self.lastRoomIndex = self.liveListArray.count -1;
    }
    return destIndex;
}

// 滚动到指定位置
    dispatch_main_async_ulsafe(^{
        if (destIndex > 0 && destIndex < self.liveListArray.count) {
            [self.tableView scrollToRowAtIndexPath:[NSIndexPath indexPathForRow:destIndex inSection:0] atScrollPosition:UITableViewScrollPositionTop animated:NO];
        } else {
            [self.tableView scrollToRowAtIndexPath:[NSIndexPath indexPathForRow:0 inSection:0] atScrollPosition:UITableViewScrollPositionTop animated:NO];
        }
    });