UICollectionView:页面控制的当前索引路径

问题描述 投票:23回答:8

我正在使用带有流布局的UICollectionView来显示单元格列表,我还有一个页面控件来指示当前页面,但似乎无法获取当前索引路径,我知道我可以获得可见单元格:

UICollectionView current visible cell index

但是可以有多个可见的单元格,即使我的每个单元格都占据了屏幕的整个宽度,如果我将它滚动到两个单元格的两半,那么它们都是可见的,所以有没有办法只获得一个当前可见细胞的指数?

谢谢

ios objective-c pagination uicollectionview uipagecontrol
8个回答
49
投票

您可以通过监视scrollViewDidScroll委托中的contentOffset来获取当前索引

它会是这样的

-(void)scrollViewDidScroll:(UIScrollView *)scrollView
{
    NSInteger currentIndex = self.collectionView.contentOffset.x / self.collectionView.frame.size.width;

}

17
投票

从中心通过NSIndexPath获取页面。

即使您的页面不等于UICollectionView的宽度。

    func scrollViewDidScroll(scrollView: UIScrollView) {
    let center = CGPoint(x: scrollView.contentOffset.x + (scrollView.frame.width / 2), y: (scrollView.frame.height / 2))
    if let ip = collectionView.indexPathForItemAtPoint(center) {
        self.pageControl.currentPage = ip.row
    }
}

12
投票

当滚动运动停止时,您肯定需要捕获可见项目。使用下一个代码来完成它。

func scrollViewDidEndDecelerating(_ scrollView: UIScrollView) {
    if let indexPath = myCollectionView.indexPathsForVisibleItems.first {
        myPageControl.currentPage = indexPath.row
    }
}

5
投票
  1. 将PageControl放在视图中或按代码设置。
  2. 设置UIScrollViewDelegate
  3. 在Collectionview-> cellForItemAtIndexPath(Method)中添加以下代码来计算页数, int pages = floor(ImageCollectionView.contentSize.width/ImageCollectionView.frame.size.width); [pageControl setNumberOfPages:pages];
  4. 添加ScrollView Delegate方法, #pragma mark - UIScrollViewDelegate for UIPageControl - (void)scrollViewDidEndDecelerating:(UIScrollView *)scrollView { CGFloat pageWidth = ImageCollectionView.frame.size.width; float currentPage = ImageCollectionView.contentOffset.x / pageWidth; if (0.0f != fmodf(currentPage, 1.0f)) { pageControl.currentPage = currentPage + 1; } else { pageControl.currentPage = currentPage; } NSLog(@"finishPage: %ld", (long)pageControl.currentPage); }

3
投票

我有类似的情况,我的流布局设置为UICollectionViewScrollDirectionHorizo​​ntal,我正在使用页面控件来显示当前页面。

我用custom flow layout实现了它。

/ ------------------------自定义标头的头文件(.h)---------------- -------- /

/**
* The customViewFlowLayoutDelegate protocol defines methods that let you coordinate with
*location of cell which is centered.
*/

@protocol CustomViewFlowLayoutDelegate <UICollectionViewDelegateFlowLayout>

/** Informs delegate about location of centered cell in grid.
*  Delegate should use this location 'indexPath' information to 
*   adjust it's conten associated with this cell. 
*   @param indexpath of cell in collection view which is centered.
*/

- (void)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout *)collectionViewLayout cellCenteredAtIndexPath:(NSIndexPath *)indexPath;
@end

@interface customViewFlowLayout : UICollectionViewFlowLayout
@property (nonatomic, weak) id<CustomViewFlowLayoutDelegate> delegate;
@end

/ -------------------自定义标题的实现文件(.m)------------------- /

@implementation customViewFlowLayout
- (void)prepareLayout {
 [super prepareLayout];
 }

static const CGFloat ACTIVE_DISTANCE = 10.0f; //Distance of given cell from center of visible rect
 static const CGFloat ITEM_SIZE = 40.0f; // Width/Height of cell.

- (id)init {
    if (self = [super init]) {
    self.scrollDirection = UICollectionViewScrollDirectionHorizontal;
    self.minimumInteritemSpacing = 60.0f;
    self.sectionInset = UIEdgeInsetsZero;
    self.itemSize = CGSizeMake(ITEM_SIZE, ITEM_SIZE);
    self.minimumLineSpacing = 0;
}
    return self;
    }

- (BOOL)shouldInvalidateLayoutForBoundsChange:(CGRect)newBounds {
    return YES;
}

- (NSArray *)layoutAttributesForElementsInRect:(CGRect)rect {
   NSArray *attributes = [super layoutAttributesForElementsInRect:rect];

CGRect visibleRect;
visibleRect.origin = self.collectionView.contentOffset;
visibleRect.size = self.collectionView.bounds.size;

for (UICollectionViewLayoutAttributes *attribute in attributes) {
    if (CGRectIntersectsRect(attribute.frame, rect)) {

        CGFloat distance = CGRectGetMidX(visibleRect) - attribute.center.x;
        // Make sure given cell is center
        if (ABS(distance) < ACTIVE_DISTANCE) {
            [self.delegate collectionView:self.collectionView layout:self cellCenteredAtIndexPath:attribute.indexPath];
        }
    }
}
return attributes;
}

包含集合视图的类必须符合我之前在自定义布局头文件中描述的协议'CustomViewFlowLayoutDelegate'。喜欢:

@interface MyCollectionViewController () <UICollectionViewDataSource, UICollectionViewDelegate, CustomViewFlowLayoutDelegate>
@property (strong, nonatomic) IBOutlet UICollectionView *collectionView;
@property (strong, nonatomic) IBOutlet UIPageControl *pageControl;
....
....
@end

有两种方法可以将自定义布局挂钩到集合视图,无论是在xib中还是在代码中,例如在viewDidLoad中:

customViewFlowLayout *flowLayout = [[customViewFlowLayout alloc]init];
flowLayout.delegate = self;
self.collectionView.collectionViewLayout = flowLayout;
self.collectionView.pagingEnabled = YES; //Matching your situation probably?

最后,在MyCollectionViewController实现文件中,实现'CustomViewFlowLayoutDelegate'的委托方法。

- (void)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout *)collectionViewLayout cellCenteredAtIndexPath:(NSIndexPath *)indexPath {
self.pageControl.currentPage = indexPath.row;

}

我希望这会有所帮助。 :)


1
投票

对于swift 4.2

@IBOutlet weak var mPageControl: UIPageControl!
@IBOutlet weak var mCollectionSlider: UICollectionView!

private var _currentIndex = 0
private var T1:Timer!
private var _indexPath:IndexPath = [0,0]

private func _GenerateNextPage(){
    self._currentIndex = mCollectionSlider.indexPathForItem(at: CGPoint.init(x: CGRect.init(origin: mCollectionSlider.contentOffset, size: mCollectionSlider.bounds.size).midX, y: CGRect.init(origin: mCollectionSlider.contentOffset, size: mCollectionSlider.bounds.size).midY))?.item ?? 0
    self.mPageControl.currentPage = self._currentIndex
}
func scrollViewDidScroll(_ scrollView: UIScrollView) {
    _SetTimer(AutoScrollInterval)
    _GenerateNextPage()
}

@objc private func _AutoScroll(){
    self._indexPath = IndexPath.init(item: self._currentIndex+1, section: 0)
    if !(self._indexPath.item < self.numberOfItems){
        _indexPath = [0,0]
    }
    self.mCollectionSlider.scrollToItem(at: self._indexPath, at: .centeredHorizontally, animated: true)
}
private func _SetTimer(_ interval:TimeInterval){
    if T1 == nil{
        T1 = Timer.scheduledTimer(timeInterval: interval , target:self , selector: #selector(_AutoScroll), userInfo: nil, repeats: true)
    }
}

你可以跳过函数_SetTimer(),那就是自动滚动


0
投票
(void)scrollViewDidScroll:(UIScrollView *)scrollView
{
    CGFloat pageWidth = _cvImagesList.frame.size.width;
    float currentPage = _cvImagesList.contentOffset.x / pageWidth;

     _pageControl.currentPage = currentPage + 1;
    NSLog(@"finishPage: %ld", (long)_pageControl.currentPage);
}

0
投票

注意 - 我发现andykkt的answer很有用但是因为它在obj-c中将它转换为swift并且还在另一个UIScrollView委托中实现了逻辑以获得更平滑的效果。

func updatePageNumber() {
    // If not case to `Int` will give an error.
    let currentPage = Int(ceil(scrollView.contentOffset.x / scrollView.frame.size.width))
    pageControl.currentPage = currentPage
}

func scrollViewDidEndDecelerating(_ scrollView: UIScrollView) {
    // This will be call when you scrolls it manually.
    updatePageNumber()
}

func scrollViewDidEndScrollingAnimation(_ scrollView: UIScrollView) {
    // This will be call when you scrolls it programmatically.
    updatePageNumber()
}

0
投票

使用UICollectionViewDelegate方法

func collectionView(_ collectionView: UICollectionView, willDisplay cell: UICollectionViewCell, forItemAt indexPath: IndexPath) {
    pageControl.currentPage = indexPath.row
}
func collectionView(_ collectionView: UICollectionView, didEndDisplaying cell: UICollectionViewCell, forItemAt indexPath: IndexPath) {
    if pageControl.currentPage == indexPath.row {
        pageControl.currentPage = collectionView.indexPath(for: collectionView.visibleCells.first!)!.row
    }
}
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