Swift ios 9: Section header change position after

Question

I have plain UITableView with many sections and rows. Sections work fine. But sometimes after reload data of table, section change position. For example it was happened when i change tabs. What could be the problem?

Image before changed tabs:

Image after changed tabs:

Update: Add code below:

override func viewWillAppear(animated: Bool) {
    super.viewWillAppear(animated)

    self.dishesListTableView.reloadData()
}

override func didReceiveMemoryWarning() {
    super.didReceiveMemoryWarning()
}


func customizeCollectionView() {
    self.collectionView.delegate = self
    self.collectionView.dataSource = self
    self.collectionView.dataProviderDelegate = self.dishesListDataProvider
    self.collectionView.showsHorizontalScrollIndicator = false
    self.collectionView.decelerationRate = UIScrollViewDecelerationRateFast
    self.collectionView.registerClass(HPCollectionViewCell.self, forCellWithReuseIdentifier: HPCollectionViewCellConstants.reuseIdentifier)
}

//MARK: - UITableViewDelegate
func customziseDishesListTableView(){
    self.dishesListTableView.delegate = self
    self.dishesListTableView.dataSource = self

    self.dishesListTableView.registerNib(UINib(nibName: DishesListSingleTableViewCell.nibName, bundle: nil), forCellReuseIdentifier: DishesListSingleTableViewCell.nibName)
    self.dishesListTableView.registerNib(UINib(nibName: DishesListSinglePizzaTableViewCell.nibName, bundle: nil), forCellReuseIdentifier: DishesListSinglePizzaTableViewCell.nibName)

    self.dishesListTableView.estimatedRowHeight = 123
    self.dishesListTableView.rowHeight = UITableViewAutomaticDimension

    if self.dishesListDataProvider.isPizza() {
        self.dishesListTableView.separatorColor = UIColor.clearColor()
    }else{
        self.dishesListTableView.separatorColor = UIColor.expSilverColor()
    }
}

func tableView(tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
    return self.dishesListDataProvider.countOfDishes(section)
}

func numberOfSectionsInTableView(tableView: UITableView) -> Int {
    return self.dishesListDataProvider.countOfKitchenTypes()
}

func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) -> UITableViewCell {
    if self.dishesListDataProvider.getDishItemByIndex(indexPath.section, indexDish: indexPath.row).isPizza() {
        let cell = tableView.dequeueReusableCellWithIdentifier(DishesListSinglePizzaTableViewCell.nibName, forIndexPath: indexPath) as! DishesListSinglePizzaTableViewCell
        cell.customizeView(self.dishesListDataProvider.getDishItemByIndex(indexPath.section, indexDish: indexPath.row), dishesListSingleTableViewCellProtocol: self, indexPath: indexPath)
        return cell
    }else{
        let cell = tableView.dequeueReusableCellWithIdentifier(DishesListSingleTableViewCell.nibName, forIndexPath: indexPath) as! DishesListSingleTableViewCell

        cell.customizeView(self.dishesListDataProvider.getDishItemByIndex(indexPath.section, indexDish: indexPath.row), dishesListSingleTableViewCellProtocol: self, indexPath: indexPath)
        return cell
    }
}

func tableView(tableView: UITableView, willDisplayFooterView view: UIView, forSection section: Int) {
    self.collectionView.scrollToIndex(section, animated: true)
    self.collectionView.changeSelectionForCellAtIndexPath(NSIndexPath(forItem: section, inSection: 0))
}

func tableView(tableView: UITableView, viewForHeaderInSection section: Int) -> UIView? {
    let sectionView = NSBundle.mainBundle().loadNibNamed(DishesListSectionView.nibName, owner: self, options: nil)[0] as! DishesListSectionView

    sectionView.customizeView(self.dishesListDataProvider.getKitchenItemByIndex(section).kitchenTypeTitle)

    return sectionView
}
//MARK: - UIScrollViewDelegate
func scrollViewDidScroll(scrollView: UIScrollView) {
    if currentSectionIndex != self.dishesListTableView.indexPathsForVisibleRows![0].section {
        currentSectionIndex = self.dishesListTableView.indexPathsForVisibleRows![0].section
        self.collectionView.scrollToIndex(currentSectionIndex, animated: true)
        self.collectionView.changeSelectionForCellAtIndexPath(NSIndexPath(forItem: currentSectionIndex, inSection: 0))
    }

}

Answer 1

It looks like the issue in estimated height for your table view cells. Due to internal optimisations system calculates the height of absent cells based on estimated height value, that's why it can position your headers on wrong calculated height (like real cells bigger or smaller than their estimated size). It usually happens when you call reloadData() in the middle of the list. As a proper solution you should avoid calling reloadData() when you want to update the content of the list with second page for example. So you should use tableView.beginUpdates() and tableView.endUpdates() and update items collection for table view. There is also new closure based API performBatchUpdates (just like it was for UICollectionView), but it's available from iOS 11.

Hope it may help to find proper solution for you