将 UICollectionView 滚动到底部 [英] Scroll UICollectionView to bottom

问题描述

我想将 UICollectionView 滚动到底部，以便最后一个项目在视图中.我曾尝试使用 scrollToItemAtIndexPath 但它似乎不起作用.我希望在通过 Parse.com 完成查询后发生这种情况

I would like to scroll the UICollectionView to the bottom so the last item is in the view. I have tried to use scrollToItemAtIndexPath but it does not seem to be working. I want this to happen after I have completed a query with Parse.com

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)    
    }

推荐答案

我添加了以下几行以在查询完成后运行.

I have added the lines below to run once the query is complete.

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)

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