oxen

Observable collections in Objective-C

oxen generates changesets when collections are modified. The main use-case for observable collections are when binding a collection to a UITableView or a UICollectionView.

Oxen changesets include the types of changes made to the collection and a snapshot of the collection after the changes hace been completed. This snapshot should be used as the backing object for table/collection views, and gives a stable model while updates are occurring.

self.array.onCollectionChanged = ^(id<OXNChangeInfo> change) {
	self.itemsArray = change.currentArray;
    if ([change isKindOfClass:[OXNItemAddedChangeInfo class]]) {
    	[self.collectionView inserItemAtIndex:[NSIndexPath indexPathForItem:change.index inSection:1]];
    }
    ... handle other cases
};

Because each oxen change creates a copy of the backing array, users are encouraged to batch updates.

[array performBatchUpdates:^{
    [array insertObject:@"" atIndex:1];
    [array removeObject:@"test"];
}];

When batch operations occur, the collectionChanged block will be invoked with a OXNBatchChangeInfo that can be enumerated.

self.array.onCollectionChanged = ^(id<OXNChangeInfo> change) {
	self.itemsArray = change.currentArray;
    if ([change isKindOfClass:[OXNBatchChangeInfo class]]) {
    	for (id<OXNChangeInfo> change in change.changes) {
    		... handle each change
    	}
    }
    ... handle other cases
};

Individual changes within the batch will all point to the same currentArray as the parent OXNBatchChangeInfo in batch operations. They will not be individually updated to reflect the backing array at the time of their change. This avoids extra copies and ensures a consistent model.

TODO

• Add an enum so switch statements can be made in place of isKindOfClass.
• Implement fast enumeration, flattening out batch updates so a single switch can be used to handle all items.