indexToScrollTo不适用于TableViewCell Swift中的最后一个CollectionView

Question

I have made a CollectionView in a TableView for vertical and horizontal scrolling and customisable cells. This works so far.

I want it to display specific Cells from the CollectionView at specific IndexPath at the first time opening the app (and if I refresh the page manually). I get the right IndexPath and it works with every TableViewCell (where the CollectionView is inside), except the last one.

Here is my Code:

import UIKit
import RealmSwift


class HomeVTwoTableViewCellSmall: UITableViewCell{

//belongs to the center Method
var onceOnly = false
var counterIndexPath = 0

//serves as a translator from ChannelName to the ChannelId
var channelOverview: [String:String] = ["Some: Values"]

//Initiaize the CellChannel Container and Live Programm
var cellChannel: Results<Community>!  
var liveProgramm: Results<Live>?

//Initialize the translated ChannelId
var channelId: String = ""
override func prepareForReuse() {
    channelId = ""
}


var channelTitle = "" {
    didSet {
        let realm = try! Realm()
        //Getting the ChannelId from Dictionary
        self.channelId = self.channelOverview[self.channelTitle]!

        //load data from Realm into variables
        self.cellChannel = realm.objects(Community.self).filter("channelId = \(self.channelId) ").sorted(byKeyPath: "startTime")
        self.liveProgramm = realm.objects(Live.self).filter("channelId = \(self.channelId) ")
        self.collectionView.reloadData()
    }
}
@IBOutlet weak var collectionView: UICollectionView!

override func awakeFromNib() {
    super.awakeFromNib()
    collectionView.delegate = self
    collectionView.dataSource = self
}
}

extension HomeVTwoTableViewCellSmall: UICollectionViewDataSource,UICollectionViewDelegate {

//MARK: Datasource Methods
func numberOfSections(in collectionView: UICollectionView) -> Int
{
    return 1
}

func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int
{
    return (cellChannel.count)
}

//gets the IndexPath to use  
func getLiveIndexPath(){
    var counter = 0
    counterIndexPath = 0
    for i in 0 ..< cellChannel.count
         {
        if (cellChannel[i].communityId != liveProgramm?[0].communityId) {
            counter += 1
        }
        else {
            counterIndexPath = counter
            return
        }
    }
}

//TODO: Center collection view on Live programm
func collectionView(_ collectionView: UICollectionView, willDisplay cell: UICollectionViewCell, forItemAt indexPath: IndexPath) {

    getLiveIndexPath()

    if !onceOnly {
        let indexToScrollTo = IndexPath(item: counterIndexPath, section: 0)
        //Change position of the Live cell by Changing position "at: ..."
        self.collectionView.scrollToItem(at: indexToScrollTo, at: .centeredHorizontally, animated: false)
        onceOnly = true
    }
}

func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell
{
    guard let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "collectionCellSmall", for: indexPath) as? HomeVTwoCollectionViewCellSmall else
    {
        fatalError("Cell has wrong type")
    }
    let realm = try! Realm()

    let selectedCommunityObject = realm.object(ofType: Community.self, forPrimaryKey: cellChannel[indexPath.row].communityId)!

    //removes the old image and Titel
    cell.imageView.image = UIImage(named: "No Image")
    cell.titleLbl.text = nil

    //inserting the channel specific data
    let url : String = (cellChannel[indexPath.row].pictureId)
    let name : String = (cellChannel[indexPath.row].communityName)
    cell.titleLbl.text = name
    cell.imageView.downloadedFrom(link :"")
    return cell
}


func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
    selectedCommunity = (cellChannel[indexPath.row].communityId)
    let home = HomeViewController()
    home.showCommunityDetail()
}
}

It seems like the in the last CollectionView the "onceOnly" boolean is already true but I don`t get why it works at the beginning but not with the last one. It scrolls but not at the right IndexPath

Answer 1

Most likely, you're experiencing a problem with a UITableViewCell being reused. What's happening is that you initially dequeue a new cell for channel A, and it's getting setup and shown correctly, including setting onceOnly to true . Then later on, this cell is getting reused by the tableview and is dequeued to be used for channel B. But in this case, onceOnly and counterIndexPath are still set with the information for A.

You're already implementing prepareForReuse . You just need to reset additional information there to get what you need.

override func prepareForReuse() {
     channelId = ""
     onceOnly = false
     counterIndexPath = 0
}