[英]UICollectionView current visible cell index
我第一次在 iPad 應用程序中使用UICollectionView
。 我已經設置UICollectionView
使其大小和單元格大小相同,這意味着一次只顯示一次單元格。
問題:現在當用戶滾動UICollectionView
我需要知道哪個單元格可見,我必須在更改時更新其他 UI 元素。 我沒有為此找到任何委托方法。 我怎樣才能做到這一點?
代碼:
[self.mainImageCollection setTag:MAIN_IMAGE_COLLECTION_VIEW];
[self.mainImageCollection registerClass:[InspirationMainImageCollectionCell class] forCellWithReuseIdentifier:@"cellIdentifier"];
[self.mainImageFlowLayout setScrollDirection:UICollectionViewScrollDirectionHorizontal];
[self.mainImageFlowLayout setMinimumInteritemSpacing:0.0f];
[self.mainImageFlowLayout setMinimumLineSpacing:0.0f];
self.mainImageFlowLayout.minimumLineSpacing = 0;
[self.mainImageCollection setPagingEnabled:YES];
[self.mainImageCollection setShowsHorizontalScrollIndicator:NO];
[self.mainImageCollection setCollectionViewLayout:self.mainImageFlowLayout];
我嘗試過的:
由於UICollectionView
符合UIScrollView
,當用戶滾動結束時我得到了UIScrollViewDelegate
方法
-(void)scrollViewDidEndDecelerating:(UIScrollView *)scrollView
但是在上面的函數中,我怎樣才能獲得UICollectionView
當前可見單元UICollectionView
?
indexPathsForVisibleItems
可能適用於大多數情況,但有時它會返回一個包含多個索引路徑的數組,並且找出您想要的路徑可能會很棘手。 在這些情況下,您可以執行以下操作:
CGRect visibleRect = (CGRect){.origin = self.collectionView.contentOffset, .size = self.collectionView.bounds.size};
CGPoint visiblePoint = CGPointMake(CGRectGetMidX(visibleRect), CGRectGetMidY(visibleRect));
NSIndexPath *visibleIndexPath = [self.collectionView indexPathForItemAtPoint:visiblePoint];
當集合視圖中的每個項目都占據整個屏幕時,這尤其有效。
迅捷版
let visibleRect = CGRect(origin: collectionView.contentOffset, size: collectionView.bounds.size)
let visiblePoint = CGPoint(x: visibleRect.midX, y: visibleRect.midY)
let visibleIndexPath = collectionView.indexPathForItem(at: visiblePoint)
[collectionView visibleCells] 方法為您提供了您想要的所有可見細胞數組。 當你想得到時使用它
- (void)scrollViewDidEndDecelerating:(UIScrollView *)scrollView{
for (UICollectionViewCell *cell in [self.mainImageCollection visibleCells]) {
NSIndexPath *indexPath = [self.mainImageCollection indexPathForCell:cell];
NSLog(@"%@",indexPath);
}
}
更新到 Swift 5:
func scrollViewDidEndDecelerating(_ scrollView: UIScrollView) {
for cell in yourCollectionView.visibleCells {
let indexPath = yourCollectionView.indexPath(for: cell)
print(indexPath)
}
}
斯威夫特5 :
func scrollViewDidEndDecelerating(_ scrollView: UIScrollView) {
var visibleRect = CGRect()
visibleRect.origin = collectionView.contentOffset
visibleRect.size = collectionView.bounds.size
let visiblePoint = CGPoint(x: visibleRect.midX, y: visibleRect.midY)
guard let indexPath = collectionView.indexPathForItem(at: visiblePoint) else { return }
print(indexPath)
}
Swift 2.2 中結合的工作答案:
func scrollViewDidEndDecelerating(scrollView: UIScrollView) {
var visibleRect = CGRect()
visibleRect.origin = self.collectionView.contentOffset
visibleRect.size = self.collectionView.bounds.size
let visiblePoint = CGPointMake(CGRectGetMidX(visibleRect), CGRectGetMidY(visibleRect))
let visibleIndexPath: NSIndexPath = self.collectionView.indexPathForItemAtPoint(visiblePoint)
guard let indexPath = visibleIndexPath else { return }
print(indexPath)
}
為了完整起見,這是最終為我工作的方法。 這是@Anthony 和@iAn 方法的組合。
- (void)scrollViewDidEndDecelerating:(UIScrollView *)scrollView {
CGRect visibleRect = (CGRect){.origin = self.collectionView.contentOffset, .size = self.collectionView.bounds.size};
CGPoint visiblePoint = CGPointMake(CGRectGetMidX(visibleRect), CGRectGetMidY(visibleRect));
NSIndexPath *visibleIndexPath = [self.collectionView indexPathForItemAtPoint:visiblePoint];
NSLog(@"%@",visibleIndexPath);
}
最好使用 UICollectionViewDelegate 方法:(Swift 3)
// Called before the cell is displayed
func collectionView(_ collectionView: UICollectionView, willDisplay cell: UICollectionViewCell, forItemAt indexPath: IndexPath) {
print(indexPath.row)
}
// Called when the cell is displayed
func collectionView(_ collectionView: UICollectionView, didEndDisplaying cell: UICollectionViewCell, forItemAt indexPath: IndexPath) {
print(indexPath.row)
}
只想為其他人添加:出於某種原因,當我使用 pagingEnabled 滾動到 collectionView 中的上一個單元格時,我沒有得到用戶可見的單元格。
所以我在 dispatch_async 中插入代碼以給它一些“空氣”,這對我有用。
-(void)scrollViewDidEndDecelerating:(UIScrollView *)scrollView
{
dispatch_async(dispatch_get_main_queue(), ^{
UICollectionViewCell * visibleCell= [[self.collectionView visibleCells] objectAtIndex:0];
[visibleCell doSomthing];
});
}
var visibleCurrentCellIndexPath: IndexPath? {
for cell in self.collectionView.visibleCells {
let indexPath = self.collectionView.indexPath(for: cell)
return indexPath
}
return nil
}
作為擴展:
extension UICollectionView {
var visibleCurrentCellIndexPath: IndexPath? {
for cell in self.visibleCells {
let indexPath = self.indexPath(for: cell)
return indexPath
}
return nil
}
}
用法:
if let indexPath = collectionView.visibleCurrentCellIndexPath {
/// do something
}
斯威夫特 3.0
最簡單的解決方案,它將為您提供可見單元格的 indexPath ..
yourCollectionView.indexPathsForVisibleItems
將返回索引路徑數組。
像這樣從數組中取出第一個對象。
yourCollectionView.indexPathsForVisibleItems.first
我想它也應該適用於 Objective-C。
對於 Swift 3.0
func scrollViewDidScroll(_ scrollView: UIScrollView) {
let visibleRect = CGRect(origin: colView.contentOffset, size: colView.bounds.size)
let visiblePoint = CGPoint(x: visibleRect.midX, y: visibleRect.midY)
let indexPath = colView.indexPathForItem(at: visiblePoint)
}
將@Anthony 的答案轉換為Swift 3.0對我來說非常有效:
func scrollViewDidScroll(_ scrollView: UIScrollView) {
var visibleRect = CGRect()
visibleRect.origin = yourCollectionView.contentOffset
visibleRect.size = yourCollectionView.bounds.size
let visiblePoint = CGPoint(x: CGFloat(visibleRect.midX), y: CGFloat(visibleRect.midY))
let visibleIndexPath: IndexPath? = yourCollectionView.indexPathForItem(at: visiblePoint)
print("Visible cell's index is : \(visibleIndexPath?.row)!")
}
您可以使用scrollViewDidEndDecelerating
: 為此
//@property (strong, nonatomic) IBOutlet UICollectionView *collectionView;
- (void)scrollViewDidEndDecelerating:(UIScrollView *)scrollView{
for (UICollectionViewCell *cell in [self.collectionView visibleCells]) {
NSIndexPath *indexPath = [self.collectionView indexPathForCell:cell];
NSUInteger lastIndex = [indexPath indexAtPosition:[indexPath length] - 1];
NSLog(@"visible cell value %d",lastIndex);
}
}
在此線程中,如果單元格全屏顯示,則有很多解決方案可以正常工作,但它們使用集合視圖邊界和可見矩形的中點 但是,此問題有一個簡單的解決方案
DispatchQueue.main.async {
let visibleCell = self.collImages.visibleCells.first
print(self.collImages.indexPath(for: visibleCell))
}
這樣,您可以獲得可見單元格的 indexPath 。 我添加了 DispatchQueue 是因為當您快速滑動時,如果在短時間內顯示下一個單元格,那么如果沒有 dispatchQueue,您將獲得簡要顯示的單元格的 indexPath,而不是屏幕上正在顯示的單元格。
這是一個老問題,但就我而言......
- (void) scrollViewWillBeginDragging:(UIScrollView *)scrollView {
_m_offsetIdx = [m_cv indexPathForCell:m_cv.visibleCells.firstObject].row;
}
- (void) scrollViewDidEndDecelerating:(UIScrollView *)scrollView {
_m_offsetIdx = [m_cv indexPathForCell:m_cv.visibleCells.lastObject].row;
}
還要檢查這個片段
let isCellVisible = collectionView.visibleCells.map { collectionView.indexPath(for: $0) }.contains(inspectingIndexPath)
試試這個,它有效。 (在下面的示例中,我有 3 個單元格。)
func scrollViewDidEndDecelerating(scrollView: UIScrollView) {
let visibleRect = CGRect(origin: self.collectionView.contentOffset, size: self.collectionView.bounds.size)
let visiblePoint = CGPointMake(CGRectGetMidX(visibleRect), CGRectGetMidY(visibleRect))
let visibleIndexPath = self.collectionView.indexPathForItemAtPoint(visiblePoint)
if let v = visibleIndexPath {
switch v.item {
case 0: setImageDescription()
break
case 1: setImageConditions()
break
case 2: setImageResults()
break
default: break
}
}
斯威夫特 3 和斯威夫特 4:
func scrollViewDidEndDecelerating(_ scrollView: UIScrollView) {
var visibleRect = CGRect()
visibleRect.origin = collectionView.contentOffset
visibleRect.size = collectionView.bounds.size
let visiblePoint = CGPoint(x: visibleRect.midX, y: visibleRect.midY)
guard let indexPath = collectionView.indexPathForItem(at: visiblePoint) else { return }
print(indexPath[1])
}
如果您想顯示實際數字,則可以添加 +1
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