我需要在 UICollectionView 中显示 3 个项目，并像这样启用分页
但我越来越像这样了
我已经制作了自定义流程，并且启用了分页但无法获得我需要的内容。我怎样才能做到这一点，或者我应该调查哪个代表，或者将我引导到一些链接，我可以从那里获得针对这种情况的帮助。
- (void)awakeFromNib
{
self.itemSize = CGSizeMake(480, 626);
self.minimumInteritemSpacing = 112;
self.minimumLineSpacing = 112;
self.scrollDirection = UICollectionViewScrollDirectionHorizontal;
self.sectionInset = UIEdgeInsetsMake(0, 272, 0, 272);
}
【问题讨论】：
标签： ios ipad uicollectionview
编辑： 演示链接：https://github.com/raheelsadiq/UICollectionView-horizontal-paging-with-3-items
经过大量搜索后，我找到了下一个滚动点并禁用分页。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];
}
我还必须使左右小而中心大，所以我用变换来做到这一点。 问题是找到索引，所以很难找到。
对于在同一方法中进行左右变换，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
}
也添加这两个宏或者你希望同时处理这两个宏
#define TRANSFORM_CELL_VALUE CGAffineTransformMakeScale(0.8, 0.8)
#define ANIMATION_SPEED 0.2
最终结果是
【讨论】：
@Raheel Sadiq 在 Swift 3 中回答的第一部分，没有转换。
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)
}
【讨论】：
Swift 3.0 基于Raheel Sadiq的完整解决方案
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)
}
}
}
【讨论】：
@raheel-sadiq 的答案很好，但我认为很难理解。在我看来，这是一个可读性很强的版本：
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 }
}
【讨论】：
您必须重写流布局的 targetContentOffsetForProposedContentOffset:withScrollingVelocity: 方法。这样你就可以捕捉到滚动视图的停止点。
-(CGPoint)targetContentOffsetForProposedContentOffset:(CGPoint)proposedContentOffset withScrollingVelocity:(CGPoint)velocity
{
CGFloat yOffset = MAXFLOAT;
CGRect proposedRect;
proposedRect.origin = proposedContentOffset;
proposedRect.size = self.collectionView.bounds.size;
CGPoint proposedCenterPoint = CGPointMake(CGRectGetMidX(proposedRect), CGRectGetMidY(proposedRect)) ;
NSArray *array = [super layoutAttributesForElementsInRect:proposedRect];
for (UICollectionViewLayoutAttributes *attributes in array)
{
CGFloat newOffset = attributes.center.y - proposedCenterPoint.y;
if ( fabsf(newOffset) < fabs(yOffset))
{
yOffset = newOffset;
}
}
return CGPointMake(proposedContentOffset.x, proposedContentOffset.y + yOffset);
}
您还需要将流布局的 sectionInset 设置为使第一个单元格和最后一个单元格居中。我的例子是高度但很容易切换到宽度。
CGFloat height = (self.collectionView.bounds.size.height / 2.0 ) - (self.itemSize.height / 2.0) ;
self.sectionInset = UIEdgeInsetsMake(height, 30.0, height, 30.0) ;
【讨论】：
我的水平集合视图分页解决方案
func scrollViewDidEndDecelerating(_ scrollView: UIScrollView) {
if scrollView == collectionView { collectionView.scrollToPage() }
}
func scrollViewDidEndDragging(_ scrollView: UIScrollView, willDecelerate decelerate: Bool) {
if scrollView == collectionView { if !decelerate { collectionView.scrollToPage() } }
}
collectionView 的小扩展
public func scrollToPage() {
var currentCellOffset = contentOffset
currentCellOffset.x += width / 2
var path = indexPathForItem(at: currentCellOffset)
if path.isNil {
currentCellOffset.x += 15
path = indexPathForItem(at: currentCellOffset)
}
if path != nil {
logInfo("Scrolling to page \(path!)")
scrollToItem(at: path!, at: .centeredHorizontally, animated: true)
}
}
【讨论】：