Objective-C Fundamentals

78 CHAPTER 4 Storing data in collections
NSLog(@"We found '%@' within the array",
valueWeAreLookingFor);
} else {
NSLog(@"We didn't find '%@' within the array",
valueWeAreLookingFor);
}
In this listing you set up a loop B to step through each element in the array. The loop
sets the loop counter variable i to the values 0 through [pets count] - 1. In the loop
you fetch the array element at index i via the objectAtIndex: method and check to
see if it’s equal to the value you are looking for c. If a match is found, you set the
found variable to YES d and break out of the for loop immediately, because there’s
no need to check any remaining array elements.
We think that’s a lot of code for such a simple task! It also allows ample opportunity
for subtle bugs to creep in. Luckily, Foundation Kit provides a much more convenient
technique to check if an array contains a specific value in the form of NSArray’s
containsObject: message:
BOOL found = [pets containsObject:@"Fish"];
if (found) {
NSLog(@"We found 'Fish' within the array");
}
Internally, containsObject: performs a similar search through the array, comparing
each element as it goes; however, this action is hidden from you, and more important,
there’s no opportunity for you to introduce errors. This technique demonstrates
another advantage of using objects: the ability to easily reuse methods instead of continually
writing them from scratch.
Sometimes you’re interested in determining not only if a value exists in an array
but also its position. The indexOfObject: message performs a similar task to containsObject:,
but instead of returning a Boolean flag to indicate if the object is
found, it returns the index at which the item is found or a special value NSNotFound if
it’s not found:
int indexOfItem = [pets indexOfObject:@"Dog"];
if (indexOfItem != NSNotFound) {
NSLog(@"We found the value 'Dog' at index %d", indexOfItem);
}
Although messages such as indexOfObject: and containsObject: allow you to
remove, or at least hide, logic that loops over each element in an array, some cases
may require such logic. For example, you may want to convert the name of each pet
into uppercase form, and NSArray has no built-in method to achieve this task. But
Objective-C and Foundation Kit provide mechanisms to perform iteration over an
array more efficiently and safely than was done in listing 4.2.