将UICollectionView滚动到底部

Question

我想将UICollectionView滚动到底部,以便最后一项位于视图中.我曾尝试使用scrollToItemAtIndexPath,但它似乎没有工作.我希望在用Parse.com完成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)    
    }

Answer 1

我在查询完成后添加了以下行来运行.

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)

Answer 2

对于 Swift -

对于水平滚动- .right

对于垂直滚动- .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)
    }

Answer 3

针对Swift 3进行了更新:

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)

Answer 4

对于Swift 3和多个部分

/**

 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)

}