When does a UITableView's contentSize get set?

Question

I have a non scrolling UITableView in a UIScrollView. I set the frame size of the UITableView to its content size.

When I add a row to the UITableView, I call insertRowsAtIndexPaths:withRowAnimation: on the UITableView. Then I call a method to resize the frame of the UITableView:

- (void)resizeTableViewFrameHeight
{
    // Table view does not scroll, so its frame height should be equal to its contentSize height
    CGRect frame = self.tableView.frame;
    frame.size = self.tableView.contentSize;
    self.tableView.frame = frame;
}

It seems though that the contentSize hasn't been updated at this point. If I manually calculate the frame in the above method based on the number of rows and sections, then the method works properly.

My question is, how can I get the UITableView to update its contentSize? I suppose I could call reloadData and that would probably do it, but it seems inefficient to reload the entire table when I'm just inserting one cell.

Answer 1

1. Add observer (in my sample in viewDidLoad

   tableView.addObserver(self, forKeyPath: "contentSize", options: .new, context: nil)
   

2. Observe value

   override func observeValue(forKeyPath keyPath: String?, of object: Any?, change: [NSKeyValueChangeKey : Any]?, context: UnsafeMutableRawPointer?) {
       if let obj = object as? UITableView {
           if obj == self.tableView && keyPath == "contentSize" {
               if let newSize = change?[NSKeyValueChangeKey.newKey] as? CGSize {
                   //do stuff here
               }
           }
       }
   }
   

3. Remove observer when not needed

   deinit {
       self.tableView.removeObserver(self, forKeyPath: "contentSize")
   }