NSMutableArray: count is a method or a property?

Question

I want to verify if I'm in the last cell of the UITable. Should I use a NSInteger property in my controller and store the value of the count of the data (it's an NSMutableArray) that populates the table?

I'm asking because I don't know if count iterates over all objects of the array to count or if it only gets me a value of a count property.

What would be better ?

store the value: myCount = [myArray count]
use directly: [myArray count]
store numberOfRows: myCount = numberOfRowsInSection:[indexPath 0]
use numberOfRows directly: numberOfRowsInSection:[indexPath 0]

Answer 1

Because the state of the table view can change at any time, depending on what the iPhone OS is doing at any given time, you will almost always want to pull state data from your model (from the array, in this case).

Answer 2

Use the method directly. It is almost certainly efficient enough. If you are having serious performance problems, use shark and instruments to discover why. If you see most of your time is being spent in calls to count, find a way to optimize that, like you suggested here. But don't optimize prematurely like this--you are just wasting your time even thinking about it.