Travel through NSArray without using loop but cursors? - ios

Question

I have an NSArray with objects inside (CLLocation). I can have 50, 100, 300 or more objects inside. In fact, this array is used while the user walking and can follow a direction. But the user can start at the middle of my NSArray, you know what I mean ?
Well, I Have to loop all the time my array to know where my user is compare to the locations in my array.
My question is: Is it possible to use a thing like in Java with a "cursor" in a list, and simply call "Next object" to travel in my array instead of loop ?
Because I need that the user walk on all location of my array.
Example:
Count of my array: 100
User start at location at index 34 (the nearest location found)
The user must do 35, 36, 37... 100 AND 0,1,2,3 ... until 33.
Hope it's clear, I really don't know how to do this without using for loop...
Thank you for help and suggestions!
Regards,
Lapinou.

Answer 1

Here's one way:
NSArray * arr = ... yourArray
int index = [arr indexOfObject:currentLocation];
index ++;
if (index == arr.count) index = 0;
id nextLocation = arr[index];
Another might be to create a global counter variable that stores the current position. If these needs to last after the user closes the app, you could write it to user defaults

Answer 2

Is looks like you are want to use NSEnumerator
NSEnumerator Class Reference
NSArray *anArray = // ... ;
NSEnumerator *enumerator = [anArray objectEnumerator];
id object;
while ((object = [enumerator nextObject])) {
// do something with object...
}

Answer 3

try this:
#interface ArrayEnumerator : NSEnumerator
{
NSArray* array;
NSInteger index;
NSInteger startIndex;
BOOL over;
}
- (id)initWithArray:(NSArray*)anArray
atIndex:(NSInteger)anIndex;
#end
#implementation ArrayEnumerator
- (id)initWithArray:(NSArray*)anArray
atIndex:(NSInteger)anIndex
{
if (self=[super init]) {
array = anArray;
index = anIndex;
startIndex = anIndex;
over = NO;
}
return self;
}
- (id)nextObject
{
if (index == [array count]) {
index = 0;
over = YES;
}
if (over && index == startIndex)
return nil;
return array[index++];
}
- (NSArray*)allObjects
{
return array;
}
#end
#implementation ViewController
- (void)viewDidLoad
{
NSArray* array = #[#0,#1,#2,#3,#4,#5,#6,#7,#8,#9];
id element;
ArrayEnumerator* enumerator = [[ArrayEnumerator alloc] initWithArray:array atIndex:4];
while (element = [enumerator nextObject])
NSLog(#"%#", element);
}
#end

Answer 4

What is wrong with a for loop?
An iterator is typically used on lists, because you can't access elements in a list by index. However you are working with an array, so you don't need an iterator, but rather some clever way of accessing the array in the desired order.
Maybe this code can provide you with some ideas. This will run from 34 to 100, then start with 0 and go up to 33.
for (int i = 34; i < 134; i++)
{
int ix = i % 100;
id whatever = arr[ix];
}

Answer 5

You can access array elements by index:
CLLocation * myLocation = myArray[34];
(or)
int i = 34;
CLLocation * myLocation = myArray[i];