将 UICollectionView 滚动到底部

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【中文标题】将 UICollectionView 滚动到底部【英文标题】:Scroll UICollectionView to bottom 【发布时间】:2014-12-03 16:49:58 【问题描述】:

我想,以便最后一项在视图中。我曾尝试使用 scrollToItemAtIndexPath 但它似乎没有工作。我希望在完成对 Parse.com 的查询后发生这种情况

谢谢

    var query = PFQuery(className:"Chat")
    //        query.whereKey("user", equalTo:currentUser)
    query.whereKey("rideId", equalTo:currentObjectId)
    query.orderByDescending("createdAt")
    query.includeKey("user")

    query.findObjectsInBackgroundWithBlock 
        (objects: [AnyObject]!, error: NSError!) -> Void in
        if error == nil 
            // The find succeeded.
            NSLog("Successfully retrieved \(objects.count) scores.")
            // Do something with the found objects
            for object in objects 
                NSLog("%@", object.objectId)

                var testId = object.objectId

                println(testId)

                self.orderedIdArray.append(testId)

                var message = object.objectForKey("message") as String
                self.messageString = message
                self.messageArray.append(self.messageString)
                println(message)

                var nameId = object.objectForKey("user") as PFUser
                var username = nameId.username as String
                self.nameString = username
                self.namesArray.append(self.nameString)

                println("username: \(username)")

                self.collectionView?.reloadData()
            

         else 
            // Log details of the failure
            NSLog("Error: %@ %@", error, error.userInfo!)
        
                    NSLog("Ordered: %@", self.orderedIdArray)    
    

【问题讨论】:

您说scrollToItemAtIndexPath“似乎不起作用”。它有什么作用? 我已将它放在self.collectionView?.reloadData() 行下,但在该行之后它不会运行任何东西。 这就是我正在使用的。这是正确的吗?let index = NSIndexPath(forItem:self.messageArray.count, inSection:0) self.collectionView?.scrollToItemAtIndexPath(index, atScrollPosition: UICollectionViewScrollPosition.Bottom, animated: true) 我的意思是我应该把代码放在...所在的位置? 【参考方案1】:

我已添加以下行,以便在查询完成后运行。

var item = self.collectionView(self.collectionView!, numberOfItemsInSection: 0) - 1
var lastItemIndex = NSIndexPath(forItem: item, inSection: 0)
self.collectionView?.scrollToItemAtIndexPath(lastItemIndex, atScrollPosition: UICollectionViewScrollPosition.Top, animated: false)

更新到 Swift 5

let item = self.collectionView(self.collectionView, numberOfItemsInSection: 0) - 1
let lastItemIndex = IndexPath(item: item, section: 0)
self.collectionView.scrollToItem(at: lastItemIndex, at: .top, animated: true)

【讨论】:

你是说修复了吗?如果是这样,那就太好了!如果不是,那么我不确定为什么这是一个答案,而不是对您的问题的编辑。 另外,您是在查询块内执行此操作,紧跟在reloadData 之后吗? 它正在工作并且它在for 语句之外。 好的。我当时不明白最初的问题(因为你说你试过了,但没有用),但我想这并不重要:只要你解决了你的问题。 顺便说一句,reloadData 也应该在for 语句之外。【参考方案2】:

对于斯威夫特 -

水平滚动 - .right

垂直滚动 - .bottom

override func viewDidLayoutSubviews() 
        let section = 0
        let lastItemIndex = self.dateCollectionView.numberOfItemsInSection(section) - 1
        let indexPath:NSIndexPath = NSIndexPath.init(forItem: lastItemIndex, inSection: section)
        self.dateCollectionView.scrollToItemAtIndexPath(indexPath, atScrollPosition: .right, animated: false)
    

【讨论】:

【参考方案3】:

适用于 Swift 3多个部分

/**

 This method scrolls the *UICollectionView* to the last item in the last section

 */

func scrollToLastItem() 

    let lastSection = collectionView.numberOfSections - 1

    let lastRow = collectionView.numberOfItems(inSection: lastSection)

    let indexPath = IndexPath(row: lastRow - 1, section: lastSection)

    self.collectionView.scrollToItem(at: indexPath, at: .right, animated: true)


【讨论】:

【参考方案4】:

为 Swift 3 更新:

let item = self.collectionView(self.collectionView!, numberOfItemsInSection: 0) - 1
let lastItemIndex = IndexPath(item: item, section: 0)
collectionView?.scrollToItem(at: lastItemIndex, at: UICollectionViewScrollPosition.top, animated: true)

【讨论】:

【参考方案5】:

斯威夫特 4

collectionView?.scrollToItem(at: IndexPath(item: 3, section: 0), at: UICollectionViewScrollPosition.top, animated: false)

【讨论】:

【参考方案6】:

斯威夫特 4:

用于水平滚动 - .right

垂直滚动 - .bottom

let lastItemIndex = self.collectionView.numberOfItems(inSection: 0) - 1
let indexPath:IndexPath = IndexPath(item: lastItemIndex, section: 0)
self.collectionView.scrollToItem(at: indexPath, at: .right, animated: false)

【讨论】:

【参考方案7】:
    lstMessages.reloadData()
    let item = self.collectionView(lstMessages, numberOfItemsInSection: 0) - 1
    let lastItemIndex = NSIndexPath(forItem: item, inSection: 0)
    lstMessages.scrollToItemAtIndexPath(lastItemIndex, atScrollPosition: UICollectionViewScrollPosition.Top, animated: false)

lstMessages 是我的 collectionView

【讨论】:

【参考方案8】:

Swift 3 更新

func viewScrollButton() 
    let lastItem = collectionView(self.collectionView!, numberOfRowsInSection: 0) - 1
    let indexPath: NSIndexPath = NSIndexPath.init(item: lastItem, section: 0)
    self.collectionView.scrollToRow(at: indexPath as IndexPath, at: .bottom, animated: false)

【讨论】:

【参考方案9】:

斯威夫特 4.2

let lastSection = self.messagesCollectionView.numberOfSections - 1
let lastRow = self.messagesCollectionView.numberOfItems(inSection: lastSection)
let indexPath = IndexPath(row: lastRow - 1, section: lastSection)
self.messagesCollectionView.scrollToItem(at: indexPath, at: UICollectionView.ScrollPosition.top, animated: true)

【讨论】:

【参考方案10】:

您可以跟踪可见视图的顶部和底部并加载下一页项目

  func scrollViewDidScroll(_ scrollView: UIScrollView) 

    if (scrollView.contentOffset.y >= (scrollView.contentSize.height - scrollView.frame.size.height)) 
        print("bottom")
    

    if (scrollView.contentOffset.y <= 0) 
        print("top")
    

【讨论】:

【参考方案11】:

Swift 5 & 4 当你想显示collectionview的最后一个单元格时调用这个函数

//MARK:- Collection view Scroll to End
func funColvScrollToEnd()

    let item = self.collectionView(self.colv!, numberOfItemsInSection: 0) - 1
    let lastItemIndex = NSIndexPath(item: item, section: 0)
    self.colv?.scrollToItem(at: lastItemIndex as IndexPath, at: .bottom, animated: false)

//MARK:- You can use .right/ .left/ .top/ .bottom  

【讨论】:

【参考方案12】:

这是我对 Swift5 的看法:

extension UICollectionView 

    public func scrollToLastItem(at scrollPosition: UICollectionView.ScrollPosition, adjustment: CGFloat = 0.0, withAdjustmentDuration duration: TimeInterval = 0.5) 
        let lastSection = self.numberOfSections - 1
        let lastRowInLastSection = self.numberOfItems(inSection: lastSection)
        if lastSection > 0, lastRowInLastSection > 0 
            let indexPath = IndexPath(row: lastRowInLastSection - 1, section: lastSection)
            let visibleIndexPaths = self.indexPathsForVisibleItems
            if !visibleIndexPaths.contains(indexPath) 
                self.self.scrollToItem(at: indexPath, at: scrollPosition, animated: true)
                UIView.animate(withDuration: duration) 
                    switch scrollPosition 
                    case .top, .bottom, .centeredVertically:
                        self.contentOffset.y += adjustment
                    case .left, .right, .centeredHorizontally:
                        self.contentOffset.x += adjustment
                    default:
                        print("Inavlid scrollPosition: \(scrollPosition)")
                    
                
            
        
    

【讨论】:

【参考方案13】:

Swift 5 如果有水平动画

func scrollToIndex(index:Int) 
 self.collectionView?.scrollToItem(at: IndexPath(item: index, section: 0), at: .centeredHorizontally, animated: true)


【讨论】:

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