Question

I have a NSMutableArray pages with several objects (instances of Page). Each Page instance has a UUID and other properties, such as contents. When a page changes, everything may change except the UUID. After a change, I would like to find out the index of a particular Page in pages by using indexOfObject:. I use the UUID to identify the index I’m looking for and this works just fine:

NSMutableArray *uuids = [[NSMutableArray alloc] init];
for (int i = 0; i < [self.pages count]; i++) {
    [uuids addObject:[[pages objectAtIndex:i] uuid]];
}

NSUInteger indexOfPage = [uuids indexOfObject:page.uuid];

Now my question is if there is a more elegant way to do this. All I really need is the index of the Page object in pages that has a given UUID.

There is
- (NSIndexSet *)indexesOfObjectsPassingTest:(BOOL (^)(id obj, NSUInteger idx, BOOL *stop))predicate or indexOfAccessibilityElement:<#(id)#> but I’m not really sure how either of these could help me out with my problem.

Answer 1

Subclass the isEqual: method in Page as follows:

- (BOOL) isEqual: (Page *) otherPage
{
    if (![otherPage isKindOfClass:[Page class]]) {
        return NO;
    }

    return [self.UUID isEqualToString: otherPage.UUID];
}

Then indexOfObject: will work correctly.

From Apple’s NSArray documentation:

Starting at index 0, each element of the array is sent an isEqual:
message until a match is found or the end of the array is reached.
This method passes the anObject parameter to each isEqual: message.
Objects are considered equal if isEqual: (declared in the NSObject
protocol) returns YES.