CODEWITHSUNDEEP
objective-ciosuitableviewindexingnsmutablearray
Mick MacCallum
Mick MacCallum

Reputation: 130222

indexOfObjectIdenticalTo: returns value outside of array count

I'm currently working on an app that populates a UITableView with items from a MPMediaItemCollection. I'm trying to add a UITableViewCellAccessoryCheckmark to the row that matches the title of the currently playing track.

I've done so by creating a mutable array of the track titles, which are also set for my cell's textLabel.text property. (for comparison purposes)

Note: This is all done in - (UITableViewCell *) tableView: (UITableView *) tableView cellForRowAtIndexPath: (NSIndexPath *) indexPath

MPMediaItem *mediaItem = (MPMediaItem *)[collectionMutableCopy objectAtIndex: row];

if (mediaItem) {
    cell.textLabel.text = [mediaItem valueForProperty:MPMediaItemPropertyTitle];
}



[mutArray insertObject:cell.textLabel.text atIndex:indexPath.row];

To the best of my knowledge this all works fine except for the below. At this point, I am trying to get the index of the currently playing tracks title and add the UITableViewCellAccessoryCheckmark to that row.

if (indexPath.row == [mutArray indexOfObjectIdenticalTo:[mainViewController.musicPlayer.nowPlayingItem valueForProperty:MPMediaItemPropertyTitle]]) {
    cell.accessoryType = UITableViewCellAccessoryCheckmark;
}

Getting to my question, I added all of the above (mostly irrelevant) code because I'm stumped on where I went wrong. When I log indexOfObjectIdenticalTo: it spits out "2147483647" every time, even though there are never more than 5 objects in the array. But why?

If anyone has any tips or pointers to help me fix this it would be greatly appreciated!

Upvotes: 1

Views: 1306

Answers (2)

kennytm
kennytm

Reputation: 523724

2147483647 just mean the object is not found.

From the documentation of -[NSArray indexOfObjectIdenticalTo:]:

Return Value

The lowest index whose corresponding array value is identical to anObject. If none of the objects in the array is identical to anObject, returns NSNotFound.

and NSNotFound is defined as:

enum {
   NSNotFound = NSIntegerMax
};

and 2147483647 = 0x7fffffff is the maximum integer on 32-bit iOS.

Please note that even if two NSString have the same content, they may not be the identical object. Two objects are identical if they share the same location, e.g.

NSString* a = @"foo";
NSString* b = a;
NSString* c = [a copy];

assert([a isEqual:b]);   // a and b are equal.
assert([a isEqual:c]);   // a and c are equal.
assert(a == b);          // a and b are identical.
assert(a != c);          // a and c are *not* identical.

I believe you just want equality test instead of identity test, i.e. 

if (indexPath.row == [mutArray indexOfObject:[....]]) {

Upvotes: 4

Paul.s
Paul.s

Reputation: 38728

Looking at the docs for NSArray

Return Value
The lowest index whose corresponding array value is identical to anObject. If none of the objects in the array is identical to anObject, returns NSNotFound.

So you should probably do a check

NSInteger index = [array indexOfObjectIdenticalTo:otherObject];

if (NSNotFound == index) {
    // ... handle not being in array
} else {
    // ... do your normal stuff
}

Upvotes: 2

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