Question

I’m trying to dynamically update cells in a UITableView. The events are triggered by data received by background threads, so everything is asynchronous and it’s impossible to predict the order of the events.

I’m not sure what the workflow is supposed to be in this case. How can I make sure that the row count and indexpath are correct when calling reloadRowsAtIndexPaths:withRowAnimation? There could still be an animation going on by a previous call to deleteRowsAtIndexPaths:withRowAnimation.

If all the changes happen at the same time, I can use beginUpdates and endUpdates, but what do I do in the above situation?

Answer 1

Hanno, I recommend using a command object model to queue the changes on the main thread.

Here’s how:

• On the callback in the main thread, append the add or delete as an object to a queue (mutable array).
• Walk the queue to add and remove objects on the main thread, with each operation being atomic (i.e gets the table status first, processes it without interruption, removes the head of the queue)
• Decide if you want to interrupt the animation if there are more commands on the queue, or wait for the animation to end then process the next queued object.

A mix of a timer and animationDidFinish callbacks should do it.