Update to the MPMediaItemCollection Category

While testing and debugging, I made a few tweaks to this category. I still haven't added reordering, but I think the methods that are here are now pretty solid. If you downloaded the earlier one, you probably want to grab the updated version, as it now codes defensively so problems aren't caused when a collection becomes empty by deletion (media item collections can't be created without at least one media item).

MPMediaItemCollection-Utils.h

#import <Foundation/Foundation.h>
#import <MediaPlayer/MediaPlayer.h>

@interface MPMediaItemCollection(Utils)
/** Returns the first media item in the collection
 */
- (MPMediaItem *)firstMediaItem;

/** Returns the last media item in the collection
 */
- (MPMediaItem *)lastMediaItem;

/** This method will return the item in this media collection at a specific index
 */
- (MPMediaItem *)mediaItemAtIndex:(NSUInteger)index;

/** Given a particular media item, this method will return the next media item in the collection.
    If there are multiple copies of the same media item in the list, it will return the one
    after the first occurrence.
 */
- (MPMediaItem *)mediaItemAfterItem:(MPMediaItem *)compare;

/** Returns the title of the media item at a given index.
 */
- (NSString *)titleForMediaItemAtIndex:(NSUInteger)index;

/** Returns YES if the given media item occurs at least once in this collection
 */
- (BOOL)containsItem:(MPMediaItem *)compare;

/** Creates a new collection by appending otherCollection to the end of this collection
 */
- (MPMediaItemCollection *)collectionByAppendingCollection:(MPMediaItemCollection *)otherCollection;

/** Creates a new collection by appending an array of media items to the end of this collection
 */
- (MPMediaItemCollection *)collectionByAppendingMediaItems:(NSArray *)items;

/** Creates a new collection by appending a single media item to the end of this collection
 */
- (MPMediaItemCollection *)collectionByAppendingMediaItem:(MPMediaItem *)item;

/** Creates a new collection based on this collection, but excluding the specified items.
 */
- (MPMediaItemCollection *)collectionByDeletingMediaItems:(NSArray *)itemsToRemove;

/** Creates a new collection based on this collection, but which doesn't include the specified media item.
 */
- (MPMediaItemCollection *)collectionByDeletingMediaItem:(MPMediaItem *)itemToRemove;

/** Creates a new collection based on this collection, but excluding the media item at the specified index
 */
- (MPMediaItemCollection *)collectionByDeletingMediaItemAtIndex:(NSUInteger)index;

/** Creates a new collection, based on this collection, but excluding the media items starting with 
    (and including) the objects at index from and ending with (and including) to.
 */
- (MPMediaItemCollection *)collectionByDeletingMediaItemsFromIndex:(NSUInteger)from toIndex:(NSUInteger)to;
@end

MPMediaItemCollection-Utils.m

#import "MPMediaItemCollection-Utils.h"

@implementation MPMediaItemCollection(Utils)
- (MPMediaItem *)firstMediaItem {
    return [[self items] objectAtIndex:0];
}

- (MPMediaItem *)lastMediaItem {
    return [[self items] lastObject];
}

- (MPMediaItem *)mediaItemAtIndex:(NSUInteger)index {
    return [[self items] objectAtIndex:index];
}

- (MPMediaItem *)mediaItemAfterItem:(MPMediaItem *)compare {
    NSArray *items = [self items];
    
    for (MPMediaItem *oneItem in items) {
        if ([oneItem isEqual:compare]) {
            // If last item, there is no index + 1
            if (![[items lastObject] isEqual: oneItem])
                return [items objectAtIndex:[items indexOfObject:oneItem] + 1];
        }
    }
    return nil;
}

- (NSString *)titleForMediaItemAtIndex:(NSUInteger)index {
    MPMediaItem *item = [[self items] objectAtIndex:index];
    return [item valueForProperty:MPMediaItemPropertyTitle];
}

- (BOOL)containsItem:(MPMediaItem *)compare {
    NSArray *items = [self items];
    
    for (MPMediaItem *oneItem in items) {
        if ([oneItem isEqual:compare])
            return YES;
    }
    return NO;
}

- (MPMediaItemCollection *)collectionByAppendingCollection:(MPMediaItemCollection *)otherCollection {
    return [self collectionByAppendingMediaItems:[otherCollection items]];
}

- (MPMediaItemCollection *)collectionByAppendingMediaItems:(NSArray *)items {
    if (items == nil || [items count] == 0)
        return nil;
    NSMutableArray *appendCollection = [[[self items] mutableCopy] autorelease];
    [appendCollection addObjectsFromArray:items];
    return [MPMediaItemCollection collectionWithItems:appendCollection];
}

- (MPMediaItemCollection *)collectionByAppendingMediaItem:(MPMediaItem *)item {
    if (item == nil)
        return nil;

    return [self collectionByAppendingMediaItems:[NSArray arrayWithObject:item]];
}

- (MPMediaItemCollection *)collectionByDeletingMediaItems:(NSArray *)itemsToRemove {
    if (itemsToRemove == nil || [itemsToRemove count] == 0)
        return [[self copy] autorelease];
    NSMutableArray *items = [[[self items] mutableCopy] autorelease];
    [items removeObjectsInArray:itemsToRemove];
    return [MPMediaItemCollection collectionWithItems:items];
}

- (MPMediaItemCollection *)collectionByDeletingMediaItem:(MPMediaItem *)itemToRemove {
    if (itemToRemove == nil)
        return [[self copy] autorelease];
    
    NSMutableArray *items = [[[self items] mutableCopy] autorelease];
    [items removeObject:itemToRemove];
    return [MPMediaItemCollection collectionWithItems:items];
}

- (MPMediaItemCollection *)collectionByDeletingMediaItemAtIndex:(NSUInteger)index {
    NSMutableArray *items = [[[self items] mutableCopy] autorelease];
    [items removeObjectAtIndex:index];
    return [items count] > 0 ? [MPMediaItemCollection collectionWithItems:items] : nil;
}

- (MPMediaItemCollection *)collectionByDeletingMediaItemsFromIndex:(NSUInteger)from toIndex:(NSUInteger)to {
    
    // Ensure from is before to
    if (to < from) {
        NSUInteger temp = from;
        to = from;
        from = temp;
    }
    
    NSMutableArray *items = [[[self items] mutableCopy] autorelease];
    [items removeObjectsInRange:NSMakeRange(from, to - from)];
    return [MPMediaItemCollection collectionWithItems:items];
}
@end