sorting through an array - objective C/iOS - ios

Question

so I'm creating a contact list app and I'm storing everything into an NSMutableArray. I've managed to get add function working perfectly. But I'm struggling with the Previous/Next functions.
I can get it to go back one object in the array when pressing previous, but i Can't get it to go back any further? here's my code: I have two extra classes, PhoneBookEntry which is a subclass of the Person class. These classes contain three strings, Firstname,lastname and studentID
- (IBAction)addPerson:(id)sender {
PhonebookEntry *person = [[PhonebookEntry alloc] init];
NSLog(#"%#",self.firstName.text);
person.firstName = self.firstName.text;
person.lastName = self.lastName.text;
person.phoneNumber = self.phoneNumber.text;
[self.entries addObject:person];
Here's my Previous button:
int length;
length = [self.entries count];
if (length > 0) {
int index;
index = [self.entries count] - 1;
NSLog (#"%d the index is", index);
NSLog(#"object %#", [self.entries objectAtIndex:index]);
} else {
NSLog (#"No contacts have been entered. No");
}
//NSLog(#"%d is the length - 1 hopefully", length);
//NSLog (#"index at %d is ", length);
I've tried removing the - 1 here:
index = [self.entries count] - 1;
and changing then on the next line putting index--; but nothing seems to work. it just goes back once.
I understand that length is getting the amount of objects in the index, and then -1 but shouldnt i-- at the end of the count / - 1 keep removing it everytime its pressed??
Any ideas? Cheers

Answer 1

You're going to keep hitting the same index with that piece of code - you need to store the state somewhere. Who is going to hold onto what the current index is? With a good designed system the model should really take care of this.
You are best off storing the current index into an ivar and updating that every time the button is pressed.
#interface OKAClass ()
#property (nonatomic, assign) NSInteger currentIndex;
#end
//... initialise the property with a default value
self.currentIndex = [self.entries count] - 1;
//... when the button is pressed decrement the index (you might want some min / max validation or use modulus to loop over and start from the top again)
NSLog(#"%#", self.entries[self.currentIndex--]);