How can I tell when a UITableView has finished reloading itself [duplicate] - ios

Question

This question already has answers here:
How can I tell when UITableView has completed ReloadData?
(18 answers)
Closed 5 years ago.
Calling tableView.reloadData() seems to initiate the reload on a different thread. If I immediately try to select a cell I've added to my data structure, it may not have been reloaded by the TableView yet. Is there a way to tell when the TableView has completed the reloadData() process. My actual code is:
DispatchQueue.main.async {
self.tableView.reloadData()
self.selectNode(node: newNode)
}
Where selectNode is my function to locate the TableViewCell displaying that node. Frequently, it fails because TableView hasn't re-displayed it yet. I can "brute force" a solution by inserting a wait loop that checks to see if TableView has requested all my rows since the reload, but I had hoped there was a more elegant solution. I'm also uncomfortable with wait loops in general.

Answer 1

I wanted to share the solution I found to the problem, as well as what it implies about how tableView.reloadData works. First, here's the code that I finally arrived at that works:
func addNewItem() {
// here we create the kind of item the user chose
//ending with this
tableView.reloadData()
queueCheckForDone()
}
func queueCheckForDone() {
DispatchQueue.main.asyncAfter(deadline: DispatchTime.now() + .milliseconds(1), execute: {
self.checkForDone()
})
}
func checkForDone() {
if items[items.count-1].viewCell != nil { // has last view cell been created
self.selectItem(item: addedItem)
} else {
queueCheckForDone()
}
}
The issue was that immediately after the reloadData, I wished to select the cell that I had just been added. But, it wasn't there immediately after the call, because the tableView hadn't finished loading. reloadData wants to run on the main thread, and my code, an event handler, was blocking it by being on the main thread. As soon as I relinquished the thread to wait, for even a millisecond, reloadData seized the thread and reloaded the whole table(> 250ms). When I finally got control again, the cell I was looking for was always there, and so I never executed the else clause of the checkForDone test.