Does UITableView have a callback for when it is done loading ALL cells?

Question

I find it very diffcult to change UIActivityIndicator on and off for data loading into a table. I set it on and then call "reload data" on my tableView and then turn it back off. I dont think that is correct, because reload data will return immediately, it doesnt block until al the data is loaded correct? So a better way it to check for a callback when all the cells are loaded?
How are you guys doing this?

Answer 1

The table isn't going to load all cells anyway.
Say you have a 100-item table of which 6 cells are visible at a time. The table view will only use tableView:cellForRowAtIndexPath: to create 6 or 7 cells.
Later on, if the user scrolls, the table view will call tableView:cellForRowAtIndexPath: some more, for the newly visible cells.
If the table view held on to every cell once it had been loaded, more and more cells would gradually get allocated until all 100 cells were in existence and holding data. That would use up a lot of memory. (What if the table has 10,000 cells?)
If the table view did the standard thing of calling \[release\] on a cell as soon as it didn't need it, memory wouldn't get used up but a lot of time would be wasted allocating and deallocating.
So the table view has a list of "cells I have but don't really want". When they encourage you to call dequeueReusableCellWithIdentifier: in your tableView:cellForRowAtIndexPath: routine, they're effectively saying "when the table is asking you for a cell for a given table entry, ask the table if it's got any unwanted cells to give you, before you go off and allocate a new one".
As far as your question is concerned, this means that the table never really finishes loading. It'll only load 6 or 7 cells at a time, and when the user scrolls, it'll load some more. Depending how you've written tableView:cellForRowAtIndexPath:, it may only ever have 6 or 7 cells in memory at a time.
It all depends what you want. If you want your activity indicator to say "I am working on giving you a display but what you see on the screen isn't what you're ultimately going to get", then
(1) Get each individual cell to start its filling-itself-with-visible-data process when you allocate/reuse the cell in tableView:cellForRowAtIndexPath:. Give the cell a unique visible appearance when you do this. When the load process is complete, get the cell to call setNeedsDisplay so that it can get repainted with the real data. The user's experience will be of a table that appears instantly, each cell with an activity indicator in it, and the activity indicators then disappear as soon as each cell finishes its work. It will look rather nice.
Or (2) do much the same, but get each cell to increment a global "loads in process" counter when it is born/reborn, and decrement it when its data have arrived. Then use that global counter to control a single UIActivityIndicator.
The key in both cases is for cell creation to be fast, and the actual loading of data to the cells (if it's slow) to be done separately.