reloadData() of UITableView with Dynamic cell heights causes jumpy scrolling

Question

To prevent jumping you should save heights of cells when they loads and give exact value in tableView:estimatedHeightForRowAtIndexPath:

Swift:

var cellHeights = [IndexPath: CGFloat]()

func tableView(_ tableView: UITableView, willDisplay cell: UITableViewCell, forRowAt indexPath: IndexPath) {
    cellHeights[indexPath] = cell.frame.size.height
}

func tableView(_ tableView: UITableView, estimatedHeightForRowAt indexPath: IndexPath) -> CGFloat {
    return cellHeights[indexPath] ?? UITableView.automaticDimension
}

Objective C:

// declare cellHeightsDictionary
NSMutableDictionary *cellHeightsDictionary = @{}.mutableCopy;

// declare table dynamic row height and create correct constraints in cells
tableView.rowHeight = UITableViewAutomaticDimension;

// save height
- (void)tableView:(UITableView *)tableView willDisplayCell:(UITableViewCell *)cell forRowAtIndexPath:(NSIndexPath *)indexPath {
    [cellHeightsDictionary setObject:@(cell.frame.size.height) forKey:indexPath];
}

// give exact height value
- (CGFloat)tableView:(UITableView *)tableView estimatedHeightForRowAtIndexPath:(NSIndexPath *)indexPath {
    NSNumber *height = [cellHeightsDictionary objectForKey:indexPath];
    if (height) return height.doubleValue;
    return UITableViewAutomaticDimension;
}

Swift 3 version of accepted answer.

var cellHeights: [IndexPath : CGFloat] = [:]


func tableView(_ tableView: UITableView, willDisplay cell: UITableViewCell, forRowAt indexPath: IndexPath) {
    cellHeights[indexPath] = cell.frame.size.height
}

func tableView(_ tableView: UITableView, estimatedHeightForRowAt indexPath: IndexPath) -> CGFloat {
    return cellHeights[indexPath] ?? 70.0 
}

The jump is because of a bad estimated height. The more the estimatedRowHeight differs from the actual height the more the table may jump when it is reloaded especially the further down it has been scrolled. This is because the table's estimated size radically differs from its actual size, forcing the table to adjust its content size and offset. So the estimated height shouldn't be a random value but close to what you think the height is going to be. I have also experienced when i set UITableViewAutomaticDimension if your cells are same type then

func viewDidLoad() {
     super.viewDidLoad()
     tableView.estimatedRowHeight = 100//close to your cell height
}

if you have variety of cells in different sections then I think the better place is

func tableView(tableView: UITableView, estimatedHeightForRowAtIndexPath indexPath: NSIndexPath) -> CGFloat {
     //return different sizes for different cells if you need to
     return 100
}

@Igor answer is working fine in this case, Swift-4 code of it.

// declaration & initialization  
var cellHeightsDictionary: [IndexPath: CGFloat] = [:]  

in following methods of UITableViewDelegate

func tableView(_ tableView: UITableView, willDisplay cell: UITableViewCell, forRowAt indexPath: IndexPath) {
  // print("Cell height: \(cell.frame.size.height)")
  self.cellHeightsDictionary[indexPath] = cell.frame.size.height
}

func tableView(_ tableView: UITableView, estimatedHeightForRowAt indexPath: IndexPath) -> CGFloat {
  if let height =  self.cellHeightsDictionary[indexPath] {
    return height
  }
  return UITableView.automaticDimension
}

I have tried all the workarounds above, but nothing worked.

After spending hours and going through all the possible frustrations, figured out a way to fix this. This solution is a life savior! Worked like a charm!

Swift 4

let lastContentOffset = tableView.contentOffset
tableView.beginUpdates()
tableView.endUpdates()
tableView.layer.removeAllAnimations()
tableView.setContentOffset(lastContentOffset, animated: false)

I added it as an extension, to make the code look cleaner and avoid writing all these lines every time I want to reload.

extension UITableView {

    func reloadWithoutAnimation() {
        let lastScrollOffset = contentOffset
        beginUpdates()
        endUpdates()
        layer.removeAllAnimations()
        setContentOffset(lastScrollOffset, animated: false)
    }
}

finally ..

tableView.reloadWithoutAnimation()

OR you could actually add these line in your UITableViewCell awakeFromNib() method

layer.shouldRasterize = true
layer.rasterizationScale = UIScreen.main.scale

and do normal reloadData()

I use more ways how to fix it:

For view controller:

var cellHeights: [IndexPath : CGFloat] = [:]


func tableView(_ tableView: UITableView, willDisplay cell: UITableViewCell, forRowAt indexPath: IndexPath) {
    cellHeights[indexPath] = cell.frame.size.height
}

func tableView(_ tableView: UITableView, estimatedHeightForRowAt indexPath: IndexPath) -> CGFloat {
    return cellHeights[indexPath] ?? 70.0 
}

as the extension for UITableView

extension UITableView {
  func reloadSectionWithoutAnimation(section: Int) {
      UIView.performWithoutAnimation {
          let offset = self.contentOffset
          self.reloadSections(IndexSet(integer: section), with: .none)
          self.contentOffset = offset
      }
  }
}

The result is

tableView.reloadSectionWithoutAnimation(section: indexPath.section)

I ran into this today and observed:

1. It's iOS 8 only, indeed.
2. Overridding cellForRowAtIndexPath doesn't help.

The fix was actually pretty simple:

Override estimatedHeightForRowAtIndexPath and make sure it returns the correct values.

With this, all weird jittering and jumping around in my UITableViews has stopped.

NOTE: I actually know the size of my cells. There are only two possible values. If your cells are truly variable-sized, then you might want to cache the cell.bounds.size.height from tableView:willDisplayCell:forRowAtIndexPath: