启用分页的 UICollectionView

Question

我必须像 Appstore iOS 应用一样创建网格视图。我想用 UICollectionView 分页来做到这一点。我也实现了代码，但无法像那样滚动。

我想要做的是在中心和两侧（左右）有一个图像，它应该显示上一个和下一个图像的一部分。我将 UICollectionView 的 Frame 设置为 320*320。单元格大小为 290*320。（单元格最小间距为 10）1

以下是描述我的要求的两个链接。提前致谢。

（这就是我想要的）2

Answer 1

完整来源是here

这支持 RTL（从右到左）

collectionView.decelerationRate = .fast


// paging
extension ViewController: UIScrollViewDelegate {
    
    func scrollViewWillBeginDragging(_ scrollView: UIScrollView) {
        self.dragStartPoint = scrollView.contentOffset
    }
    
    func scrollViewWillEndDragging(_ scrollView: UIScrollView, withVelocity velocity: CGPoint, targetContentOffset: UnsafeMutablePointer<CGPoint>) {
        let isRTL = UIApplication.shared.userInterfaceLayoutDirection == .rightToLeft
        let pageWidth = UIScreen.main.bounds.size.width - ViewController.left - ViewController.right + ViewController.lineSpacing
        
        if scrollView.contentOffset.x == targetContentOffset.pointee.x { // no decelerate
            if fabsf(Float(self.dragStartPoint.x - scrollView.contentOffset.x)) > 40 { // min move distance = 40
                let dragLeft = self.dragStartPoint.x < scrollView.contentOffset.x
                if dragLeft {
                    self.currentPage = isRTL ? self.currentPage - 1 : self.currentPage + 1
                } else {
                    self.currentPage = isRTL ? self.currentPage + 1 : self.currentPage - 1
                }
            }
        } else if scrollView.contentOffset.x > targetContentOffset.pointee.x {
            let maxRight = scrollView.contentSize.width - UIScreen.main.bounds.size.width
            if scrollView.contentOffset.x <= maxRight { // not right bounce
                self.currentPage = isRTL ? self.currentPage + 1 : self.currentPage - 1
            }
        } else {
            if scrollView.contentOffset.x >= 0 { // not left bounce
                self.currentPage = isRTL ? self.currentPage - 1 : self.currentPage + 1
            }
        }
        
        self.currentPage = max(0, self.currentPage)
        self.currentPage = min(self.numberOfPages - 1, self.currentPage)
        
        var offset = targetContentOffset.pointee
        if isRTL {
            offset.x = CGFloat(self.numberOfPages - self.currentPage - 1) * pageWidth
        } else {
            offset.x = CGFloat(self.currentPage) * pageWidth
        }
        targetContentOffset.pointee = offset
    }
}

Answer 2

只需使用 collectionView.isPagingEnabled = true;

Answer 3

这是Rickster 答案的工作 swift4 版本：

func scrollViewWillEndDragging(_ scrollView: UIScrollView, withVelocity velocity: CGPoint, targetContentOffset: UnsafeMutablePointer<CGPoint>) {

    let cellWidth = 174 as CGFloat
    let cellPadding = 10 as CGFloat

    var page = (scrollView.contentOffset.x - cellWidth / 2) / (cellWidth + cellPadding) + 1

    if (velocity.x > 0) { page += 1 }
    if (velocity.x < 0) { page -= 1 }

    page = max(page,0)

    targetContentOffset.pointee.x = page * (cellWidth + cellPadding)
}

Answer 4

参考 Rickster 的回答，我用 Swift 4 重写：

/* paging */
extension AlbumViewController {

    /* In case the user scrolls for a long swipe, the scroll view should animate to the nearest page when the scrollview decelerated. */
    override func scrollViewDidEndDecelerating(_ scrollView: UIScrollView) {
        scrollToPage(scrollView, withVelocity: CGPoint(x:0, y:0))
    }

    override func scrollViewWillEndDragging(_ scrollView: UIScrollView, withVelocity velocity: CGPoint, targetContentOffset: UnsafeMutablePointer<CGPoint>) {
        scrollToPage(scrollView, withVelocity: velocity)
    }

    func scrollToPage(_ scrollView: UIScrollView, withVelocity velocity: CGPoint) {
        let cellWidth: CGFloat = cellSize
        let cellPadding: CGFloat = 10

        var page: Int = Int((scrollView.contentOffset.x - cellWidth / 2) / (cellWidth + cellPadding) + 1)
        if velocity.x > 0 {
            page += 1
        }
        if velocity.x < 0 {
            page -= 1
        }
        page = max(page, 0)
        let newOffset: CGFloat = CGFloat(page) * (cellWidth + cellPadding)

        scrollView.setContentOffset(CGPoint(x:newOffset, y:0), animated: true)
    }
}

Answer 5

我接受了shtefane's answer 并对其进行了改进。输入您自己的 cellWidth 和 cellPadding 值。

- (void)scrollViewWillEndDragging:(UIScrollView *)scrollView
                     withVelocity:(CGPoint)velocity
              targetContentOffset:(inout CGPoint *)targetContentOffset
{
    CGFloat cellWidth = self.cellWidth;
    CGFloat cellPadding = 9;

    NSInteger page = (scrollView.contentOffset.x - cellWidth / 2) / (cellWidth + cellPadding) + 1;

    if (velocity.x > 0) page++;
    if (velocity.x < 0) page--;
    page = MAX(page,0);

    CGFloat newOffset = page * (cellWidth + cellPadding);
    targetContentOffset->x = newOffset;
}

Answer 6

您是否尝试将 UICollectionViewFlowLayout 的滚动方向设置为水平？

[yourFlowLayout setScrollDirection:UICollectionViewScrollDirectionHorizontal];

您需要像这样在集合视图上启用分页：

[yourCollectionView setPagingEnabled:YES];

Answer 7

如果您在 collectionView 中使用分页，它将滚动一页而不是一个单元格。您可以禁用分页并实现 ScrollViewDelegate

- (void)scrollViewWillEndDragging:(UIScrollView *)scrollView withVelocity:(CGPoint)velocity targetContentOffset:(inout CGPoint *)targetContentOffset
 {
     CGFloat pageW = 300;
    int page = scrollView.contentOffset.x / pageW;

    CGFloat newOffset =(page + ((velocity.x > 0)? 1 : -1)) * (pageW - 20);
    CGPoint target = CGPointMake(newOffset, 0);
    targetContentOffset = ⌖
    NSLog(@"end Drag at %f /%i /%f",scrollView.contentOffset.x, page, velocity.x);

 }

与标准分页只有一个不同：如果快速拖动 Collection 将滚动多个单元格。 并且不要忘记添加 UIScrollViewDelegate