检测 UICollectionView 中的页面变化

Question

I tried finding this question for a while but could not find this problem's answer. My problem is that i have a UICollectionView and the Scroll Direction is Horizontal with Paging Enabled . My problem is that i want to keep the tack of the current page number on which the user is, so i created an int variable and now want to add or subtract it by 1 each time the user swipes right or left. I tried using scrollView 's delegate

- (void)scrollViewDidScroll:(UIScrollView *)scrollView

but when the user swipes right or left, it is called as many number of the times as the number of columns on a page in the UICollectionView plus it wont let me know that whether the user went to the next page or the previous one.

Answer 1

Swift 3 Xcode 8.2

func scrollViewDidEndDecelerating(_ scrollView: UIScrollView) {
        let x = scrollView.contentOffset.x
        let w = scrollView.bounds.size.width
        let currentPage = Int(ceil(x/w))
        // Do whatever with currentPage.
}

Answer 2

Use :

- (void)scrollViewDidEndDecelerating:(UIScrollView *)scrollView
{
    CGFloat pageWidth = collectionView.frame.size.width;
    float currentPage = collectionView.contentOffset.x / pageWidth;

    if (0.0f != fmodf(currentPage, 1.0f))
    {
        pageControl.currentPage = currentPage + 1;
    }
    else
    {
        pageControl.currentPage = currentPage;
    }

    NSLog(@"Page Number : %ld", (long)pageControl.currentPage);
}

And if you are not using any pageControl, then ceil(currentPage) will be your current page number.

Answer 3

Based on @Shankar BS 's answer I've implemented it like this in Swit. Keep in mind that CollectionViewDelegate conforms to ScrollViewDelegate:

func scrollViewDidEndDecelerating(_ scrollView: UIScrollView) {
    let pageWidth = scrollView.frame.size.width
    let page = Int(floor((scrollView.contentOffset.x - pageWidth / 2) / pageWidth) + 1)
    print("page = \(page)")
}

Answer 4

You can get the current page like below, index will be from 0 to (total page - 1)

-(void)scrollViewDidEndDecelerating:(UIScrollView *)scrollView
 {
    CGFloat pageWidth = scrollView.frame.size.width;
    int page = floor((scrollView.contentOffset.x - pageWidth / 2) / pageWidth) + 1;
    NSLog(@"Current page -> %d",page);
}

Answer 5

SWIFT 5

For example, put this method in your ViewController with extensions UICollectionViewDelegate,UICollectionViewDataSource

func scrollViewDidEndDecelerating(_ scrollView: UIScrollView) {
        let pageWidth = scrollView.frame.size.width
        let page = Int(floor((scrollView.contentOffset.x - pageWidth / 2) / pageWidth) + 1)
        print("page = \(page)")
    }

Answer 6

Swift 2.2

 func scrollViewDidEndDecelerating(scrollView: UIScrollView) {
    let x = collectionView.contentOffset.x
    let w = collectionView.bounds.size.width
    let currentPage = Int(ceil(x/w))
    print("Current Page: \(currentPage)")
}

Answer 7

You can get the currentPage this way when the user end the dragging:

Swift 5.6 Tested and works!

func scrollViewWillEndDragging(_ scrollView: UIScrollView, withVelocity velocity: CGPoint, targetContentOffset: UnsafeMutablePointer<CGPoint>) {
    let itemWidth = collectionView.frame.width // Get the itemWidth. In my case every cell was the same width as the collectionView itself
    let contentOffset = targetContentOffset.pointee.x

    let targetItem = lround(Double(contentOffset/itemWidth))
    let targetIndex = targetItem % YOUR_ARRAY.count // numberOfItems which shows in the collection view
    print(targetIndex)
}

Answer 8

Xamarin.iOS:

You can override DecelerationEnded method of UICollectionViewDelegate or subscribe to DecelerationEnded event of UICollectionView (custom delegate will be used under the hood).

public override void DecelerationEnded(UIScrollView scrollView)
{
    var x = scrollView.ContentOffset.X;
    var w = scrollView.Bounds.Size.Width;
    var currentPage = Math.Ceiling(x / w);

    // use currentPage here
}