UICollectionView horizontal paging with 3 items

Question

I need to show 3 items in a UICollectionView, with paging enabled like this

but I am getting like this

I have made custom flow, plus paging is enabled but not able to get what i need. How can i achieve this or which delegate should i look into, or direct me to some link from where i can get help for this scenario.

- (void)awakeFromNib
{
    self.itemSize = CGSizeMake(480, 626);
    self.minimumInteritemSpacing = 112;
    self.minimumLineSpacing = 112;
    self.scrollDirection = UICollectionViewScrollDirectionHorizontal;
    self.sectionInset = UIEdgeInsetsMake(0, 272, 0, 272);
}

Answer 1

编辑:演示链接:https://github.com/raheelsadiq/UICollectionView-horizo​​ntal-paging-with-3-items

经过大量搜索,我做了它,找到下一个要滚动的点并禁用分页.在scrollviewWillEndDragging中滚动到下一个单元格x.

- (void)scrollViewWillEndDragging:(UIScrollView *)scrollView withVelocity:(CGPoint)velocity targetContentOffset:(inout CGPoint *)targetContentOffset
{

    float pageWidth = 480 + 50; // width + space

    float currentOffset = scrollView.contentOffset.x;
    float targetOffset = targetContentOffset->x;
    float newTargetOffset = 0;

    if (targetOffset > currentOffset)
        newTargetOffset = ceilf(currentOffset / pageWidth) * pageWidth;
    else
        newTargetOffset = floorf(currentOffset / pageWidth) * pageWidth;

    if (newTargetOffset < 0)
        newTargetOffset = 0;
    else if (newTargetOffset > scrollView.contentSize.width)
        newTargetOffset = scrollView.contentSize.width;

    targetContentOffset->x = currentOffset;
    [scrollView setContentOffset:CGPointMake(newTargetOffset, scrollView.contentOffset.y) animated:YES];
}

我还必须使左右小,中心大,所以我做了变换.问题是找到索引,因此很难找到.

对于在同一方法中左右变换,请使用newTargetOffset

int index = newTargetOffset / pageWidth;

if (index == 0) { // If first index 
    UICollectionViewCell *cell = [self.collectionView cellForItemAtIndexPath:[NSIndexPath indexPathForItem:index  inSection:0]];

    [UIView animateWithDuration:ANIMATION_SPEED animations:^{
        cell.transform = CGAffineTransformIdentity;
    }];
    cell = [self.collectionView cellForItemAtIndexPath:[NSIndexPath indexPathForItem:index + 1  inSection:0]];
    [UIView animateWithDuration:ANIMATION_SPEED animations:^{
        cell.transform = TRANSFORM_CELL_VALUE;
    }];
}else{
    UICollectionViewCell *cell = [self.collectionView cellForItemAtIndexPath:[NSIndexPath indexPathForItem:index inSection:0]];
    [UIView animateWithDuration:ANIMATION_SPEED animations:^{
        cell.transform = CGAffineTransformIdentity;
    }];

    index --; // left
    cell = [self.collectionView cellForItemAtIndexPath:[NSIndexPath indexPathForItem:index inSection:0]];
    [UIView animateWithDuration:ANIMATION_SPEED animations:^{
        cell.transform = TRANSFORM_CELL_VALUE;
    }];

    index ++;
    index ++; // right
    cell = [self.collectionView cellForItemAtIndexPath:[NSIndexPath indexPathForItem:index inSection:0]];
    [UIView animateWithDuration:ANIMATION_SPEED animations:^{
        cell.transform = TRANSFORM_CELL_VALUE;
    }];
}

并在cellForRowAtIndex中添加

if (indexPath.row == 0 && isfirstTimeTransform) { // make a bool and set YES initially, this check will prevent fist load transform
    isfirstTimeTransform = NO;
}else{
    cell.transform = TRANSFORM_CELL_VALUE; // the new cell will always be transform and without animation 
}

也可以添加这两个宏,或者您希望同时处理这两个宏

#define TRANSFORM_CELL_VALUE CGAffineTransformMakeScale(0.8, 0.8)
#define ANIMATION_SPEED 0.2

最终的结果是

Answer 2

@Raheel Sadiq的第一部分在Swift 3中回答,没有Transform.

func scrollViewWillEndDragging(_ scrollView: UIScrollView, withVelocity velocity: CGPoint, targetContentOffset: UnsafeMutablePointer<CGPoint>) {
        let pageWidth: Float = Float(self.collectionView.frame.width / 3) //480 + 50
        // width + space
        let currentOffset: Float = Float(scrollView.contentOffset.x)
        let targetOffset: Float = Float(targetContentOffset.pointee.x)
        var newTargetOffset: Float = 0
        if targetOffset > currentOffset {
            newTargetOffset = ceilf(currentOffset / pageWidth) * pageWidth
        }
        else {
            newTargetOffset = floorf(currentOffset / pageWidth) * pageWidth
        }
        if newTargetOffset < 0 {
            newTargetOffset = 0
        }
        else if (newTargetOffset > Float(scrollView.contentSize.width)){
            newTargetOffset = Float(Float(scrollView.contentSize.width))
        }

        targetContentOffset.pointee.x = CGFloat(currentOffset)
        scrollView.setContentOffset(CGPoint(x: CGFloat(newTargetOffset), y: scrollView.contentOffset.y), animated: true)

    }

Answer 3

基于Raheel Sadiq的Swift 3.0完整解决方案

var isfirstTimeTransform:Bool = true

func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {


    let cell : UICollectionViewCell = collectionView.dequeueReusableCell(withReuseIdentifier: "YourCustomViewCell", for: indexPath)

    if (indexPath.row == 0 && isfirstTimeTransform) { 
        isfirstTimeTransform = false
    }else{
        cell.transform = CGAffineTransform(scaleX: 0.8, y: 0.8) 
    }

    return cell
}

func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAt indexPath: IndexPath) -> CGSize {

    return CGSize(width: collectionView.bounds.width/3, height: collectionView.bounds.height)
}

func scrollViewWillEndDragging(_ scrollView: UIScrollView, withVelocity velocity: CGPoint, targetContentOffset: UnsafeMutablePointer<CGPoint>) {
    // Simulate "Page" Function
    let pageWidth: Float = Float(self.collectionView.frame.width/3 + 20)
    let currentOffset: Float = Float(scrollView.contentOffset.x)
    let targetOffset: Float = Float(targetContentOffset.pointee.x)
    var newTargetOffset: Float = 0
    if targetOffset > currentOffset {
        newTargetOffset = ceilf(currentOffset / pageWidth) * pageWidth
    }
    else {
        newTargetOffset = floorf(currentOffset / pageWidth) * pageWidth
    }
    if newTargetOffset < 0 {
        newTargetOffset = 0
    }
    else if (newTargetOffset > Float(scrollView.contentSize.width)){
        newTargetOffset = Float(Float(scrollView.contentSize.width))
    }

    targetContentOffset.pointee.x = CGFloat(currentOffset)
    scrollView.setContentOffset(CGPoint(x: CGFloat(newTargetOffset), y: scrollView.contentOffset.y), animated: true)

    // Make Transition Effects for cells
    let duration = 0.2
    var index = newTargetOffset / pageWidth;
    var cell:UICollectionViewCell = self.collectionView.cellForItem(at: IndexPath(row: Int(index), section: 0))!
    if (index == 0) { // If first index
        UIView.animate(withDuration: duration, delay: 0.0, options: [ .curveEaseOut], animations: {
            cell.transform = CGAffineTransform.identity
        }, completion: nil)
        index += 1
        cell = self.collectionView.cellForItem(at: IndexPath(row: Int(index), section: 0))!
        UIView.animate(withDuration: duration, delay: 0.0, options: [ .curveEaseOut], animations: {
            cell.transform = CGAffineTransform(scaleX: 0.8, y: 0.8)
        }, completion: nil)
    }else{
        UIView.animate(withDuration: duration, delay: 0.0, options: [ .curveEaseOut], animations: {
            cell.transform = CGAffineTransform.identity;
        }, completion: nil)

        index -= 1 // left
        if let cell = self.collectionView.cellForItem(at: IndexPath(row: Int(index), section: 0)) {
            UIView.animate(withDuration: duration, delay: 0.0, options: [ .curveEaseOut], animations: {
                cell.transform = CGAffineTransform(scaleX: 0.8, y: 0.8);
            }, completion: nil)
        }

        index += 1
        index += 1 // right
        if let cell = self.collectionView.cellForItem(at: IndexPath(row: Int(index), section: 0)) {
            UIView.animate(withDuration: duration, delay: 0.0, options: [ .curveEaseOut], animations: {
                cell.transform = CGAffineTransform(scaleX: 0.8, y: 0.8);
            }, completion: nil)
        }
    }

}

Answer 4

@ raheel-sadiq答案很棒但很难理解,我想.在我看来,这是一个非常易读的版本:

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

        //minimumLineSpacing and insetForSection are two constants in my code

        //this cell width is for my case, adapt to yours
        let cellItemWidth = view.frame.width - (insetForSection.left + insetForSection.right)
        let pageWidth = Float(cellItemWidth + minimumLineSpacing)

        let offsetXAfterDragging = Float(scrollView.contentOffset.x)
        let targetOffsetX = Float(targetContentOffset.pointee.x)

        let pagesCountForOffset = pagesCount(forOffset: offsetXAfterDragging, withTargetOffset: targetOffsetX, pageWidth: pageWidth)

        var newTargetOffsetX = pagesCountForOffset * pageWidth

        keepNewTargetInBounds(&newTargetOffsetX, scrollView)

        //ignore target
        targetContentOffset.pointee.x = CGFloat(offsetXAfterDragging)

        let newTargetPoint = CGPoint(x: CGFloat(newTargetOffsetX), y: scrollView.contentOffset.y)
        scrollView.setContentOffset(newTargetPoint, animated: true)

        //if you're using pageControl
        pageControl.currentPage = Int(newTargetOffsetX / pageWidth)

    }

    fileprivate func pagesCount(forOffset offset: Float, withTargetOffset targetOffset: Float, pageWidth: Float) -> Float {
        let isRightDirection = targetOffset > offset
        let roundFunction = isRightDirection ? ceilf : floorf
        let pagesCountForOffset = roundFunction(offset / pageWidth)
        return pagesCountForOffset
    }

    fileprivate func keepNewTargetInBounds(_ newTargetOffsetX: inout Float, _ scrollView: UIScrollView) {
        if newTargetOffsetX < 0 { newTargetOffsetX = 0 }
        let contentSizeWidth = Float(scrollView.contentSize.width)
        if newTargetOffsetX > contentSizeWidth { newTargetOffsetX = contentSizeWidth }
    }