UICollectionView监听滚动距离及获取当前index

前言

由于开发中遇到一个既有按钮可以点击展示上一个和下一个，也可以手动滑动展示上一个下一个，导致监听UICollectionView到底展示的是哪个indexPath比较麻烦，特记录一下

参考：

• UITableView、UICollectionView 滚动结束的监测(类似ViewDidAppear)
• 如何获取顶部CollectionView当前显示的cell的indexPath

监听滚动停止：

注意：页面中点击上一个、下一个按钮调用的- (void)scrollToItemAtIndexPath:(NSIndexPath *)indexPath atScrollPosition:(UICollectionViewScrollPosition)scrollPosition animated:(BOOL)animated;不会走这个滚动的回调

- (void)scrollViewDidEndDecelerating:(UIScrollView *)scrollView {
    // 停止类型1、停止类型2
    BOOL scrollToScrollStop = !scrollView.tracking && !scrollView.dragging &&    !scrollView.decelerating;
    if (scrollToScrollStop) {
        [self scrollViewDidEndScroll];
    }
}

- (void)scrollViewDidEndDragging:(UIScrollView *)scrollView willDecelerate:(BOOL)decelerate {
    if (!decelerate) {
        // 停止类型3
        BOOL dragToDragStop = scrollView.tracking && !scrollView.dragging && !scrollView.decelerating;
        if (dragToDragStop) {
            [self scrollViewDidEndScroll];
        }
    }
}

#pragma mark - scrollView 停止滚动监测
- (void)scrollViewDidEndScroll {
   NSArray *indexPaths = [self.collectionView indexPathsForVisibleItems];
    NSIndexPath *indexPath = indexPaths.firstObject;
    // 将collectionView在控制器view的中心点转化成collectionView上的坐标
//    CGPoint pInView = [self convertPoint:self.collectionView.center toView:self.collectionView];
//    // 获取这一点的indexPath
//    NSIndexPath *indexPath = [self.collectionView indexPathForItemAtPoint:pInView];
   

}

调用UICollectionView的reloadData后立刻调用scrollToItemAtIndexPath...,则scrollToItemAtIndex不会起作用，需要在relaodData后延迟一下调用

- (void)awakeFromNib {
    [super awakeFromNib];
    self.selectionStyle = UITableViewCellSelectionStyleNone;
    [self.collectionView registerNib:[UINib nibWithNibName:@"xxxxCollectionViewCell" bundle:nil] forCellWithReuseIdentifier:@"xxxxCollectionViewCell"];
    self.collectionView.backgroundColor = [UIColor whiteColor];
    self.collectionView.dataSource = self;
    self.collectionView.delegate = self;
    self.collectionView.scrollEnabled = YES;
    self.collectionView.pagingEnabled = YES;
    self.collectionView.showsHorizontalScrollIndicator = NO;
    self.selectionStyle = UITableViewCellSelectionStyleNone;
}

- (void)setSelected:(BOOL)selected animated:(BOOL)animated {
    [super setSelected:selected animated:animated];

    // Configure the view for the selected state
}
- (NSInteger)numberOfSectionsInCollectionView:(UICollectionView *)collectionView
{
    return 1;
}
- (NSInteger)collectionView:(UICollectionView *)collectionView numberOfItemsInSection:(NSInteger)section
{
    return self.dataList.count;
}
- (CGSize)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout *)collectionViewLayout sizeForItemAtIndexPath:(NSIndexPath *)indexPath
{
    return CGSizeMake(Main_Screen_Width, collectionView.height);
}

- (UIEdgeInsets)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout*)collectionViewLayout insetForSectionAtIndex:(NSInteger)section {
    return UIEdgeInsetsMake(0, 0, 0, 0);
}
- (CGFloat)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout *)collectionViewLayout minimumLineSpacingForSectionAtIndex:(NSInteger)section
{
    return 0;
}
- (CGFloat)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout *)collectionViewLayout minimumInteritemSpacingForSectionAtIndex:(NSInteger)section
{
    return 0;
}
- (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath
{
    xxxxCollectionViewCell *cell = [collectionView dequeueReusableCellWithReuseIdentifier:@"xxxxCollectionViewCell" forIndexPath:indexPath];
    XXXModel *model = self.dataList[indexPath.item];
    cell.model = model;
    return cell;
}
- (void)scrollViewDidEndDecelerating:(UIScrollView *)scrollView {
    // 停止类型1、停止类型2
    BOOL scrollToScrollStop = !scrollView.tracking && !scrollView.dragging &&    !scrollView.decelerating;
    if (scrollToScrollStop) {
        [self scrollViewDidEndScroll];
    }
}

- (void)scrollViewDidEndDragging:(UIScrollView *)scrollView willDecelerate:(BOOL)decelerate {
    if (!decelerate) {
        // 停止类型3
        BOOL dragToDragStop = scrollView.tracking && !scrollView.dragging && !scrollView.decelerating;
        if (dragToDragStop) {
            [self scrollViewDidEndScroll];
        }
    }
}

#pragma mark - scrollView 停止滚动监测
- (void)scrollViewDidEndScroll {
   NSArray *indexPaths = [self.collectionView indexPathsForVisibleItems];
    NSIndexPath *indexPath = indexPaths.firstObject;
    // 将collectionView在控制器view的中心点转化成collectionView上的坐标
//    CGPoint pInView = [self convertPoint:self.collectionView.center toView:self.collectionView];
//    // 获取这一点的indexPath
//    NSIndexPath *indexPath = [self.collectionView indexPathForItemAtPoint:pInView];
    self.selectIndex = indexPath.item;
    [self updateShowTitle];
}

- (IBAction)preBtnClicked:(id)sender {
    self.selectIndex -=1;
    [self updateShow];
    
}
- (IBAction)nextBtnClicked:(id)sender {
    self.selectIndex +=1;
    [self updateShow];
}

- (void)setDataList:(NSArray<VIPLevelDataModel *> *)dataList
{
    _dataList = dataList;
    [self initUpdateShow];
}
- (void)updateShowTitle
{
    if(self.dataList.count == 0){
        return;
    }
    if(self.selectIndex == 0){
        self.preBtn.enabled = NO;
    }else{
        self.preBtn.enabled = YES;
    }
    if(self.selectIndex >= self.dataList.count-1){
        self.nextBtn.enabled = NO;
    }else{
        self.nextBtn.enabled = YES;
    }
    NSString *imageName = [NSString stringWithFormat:@"vip_red%ld",self.selectIndex];
    self.vipImage.image = [UIImage imageNamed:imageName];
}
- (void)initUpdateShow
{
    if(self.dataList.count == 0){
        return;
    }
    [self updateShowTitle];
    [self.collectionView reloadData];
    WS(weakSelf)
    NSIndexPath *indexPath = [NSIndexPath indexPathForItem:self
.selectIndex inSection:0];
    dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(0.1 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{
        [weakSelf.collectionView scrollToItemAtIndexPath:indexPath atScrollPosition:UICollectionViewScrollPositionCenteredHorizontally animated:NO];
    });

}
- (void)updateShow
{
    if( self.dataList.count == 0){
        return;
    }
    [self updateShowTitle];
    NSIndexPath *indexPath = [NSIndexPath indexPathForItem:self.selectIndex inSection:0];
    [self.collectionView scrollToItemAtIndexPath:indexPath atScrollPosition:UICollectionViewScrollPositionCenteredHorizontally animated:YES];
}