This is a set of simple categories that help with a common pattern I use for updating array-backed UITableViews and UICollectionViews.
It extends NSArray to provide simple diff functionality. You provide the initial array, the updated array, and an identity comparison block, and the method returns an NSDictionary of NSIndexSets with the inserted, deleted, moved and unmoved indexes.
Categories are provided for UITableView and UICollectionView that take the IndexSet dictionary and perform the updates as a batch with row/cell animation. Items that have not moved from their initial position may optionally be reloaded.
- (void)updateWithItems:(NSArray *)items {
NSDictionary* indexChangeSets = [NSArray indexChangeSetsForUpdatedList:items
previousList:self.items
identityComparator:^NSComparisonResult(NSDictionary* a, NSDictionary* b) {
// This block should determine if the items in the list have the same identity or not
return [a[@"id"] compare:b[@"id"]];
}];
[self.collectionView performBatchUpdates:^{
self.items = items;
[self.collectionView updateSection:0 withChangeSet:indexChangeSets reloadingUnmoved:YES];
} completion:nil];
}- (void)updateWithItems:(NSArray *)items {
NSDictionary* indexChangeSets = [NSArray indexChangeSetsForUpdatedList:items
previousList:self.items
identityComparator:^NSComparisonResult(NSDictionary* a, NSDictionary* b) {
// This block should determine if the items in the list have the same identity or not
return [a[@"id"] compare:b[@"id"]];
}];
self.items = items;
[self.tableView beginUpdates];
[self.tableView updateSection:0 withChangeSet:indexChangeSets];
[self.tableView endUpdates];
}Note: To use this library in Swift, you must import the library header file into your project's Bridging Header file.
#import "LMArrayChangeSets.h"
More details about mixing Objective-C and Swift code are available here.
func updateWithItems(items:NSArray) {
let indexChanges = NSArray.indexChangeSetsForUpdatedList(items, previousList: self.items) {
(anyA:AnyObject!, anyB:AnyObject!) -> NSComparisonResult in
let a = anyA as MyObject
let b = anyB as MyObject
// This should determine if the items have the same identity or not
return a.id.compare(b.id)
}
self.collectionView!.performBatchUpdates({
() -> Void in
self.items = items
self.collectionView!.updateSection(0, withChangeSet:indexChanges)
},
completion:nil
)
}func updateWithItems(items:NSArray) {
let indexChanges = NSArray.indexChangeSetsForUpdatedList(items, previousList: self.items) {
(anyA:AnyObject!, anyB:AnyObject!) -> NSComparisonResult in
let a = anyA as MyObject
let b = anyB as MyObject
// This should determine if the items have the same identity or not
return a.id.compare(b.id)
}
self.items = items
self.tableView!.beginUpdates()
self.tableView!.updateSection(0, withChangeSet:indexChanges, reloadingUnmoved:true)
self.tableView!.endUpdates()
}Please Note: The algorithm used to determine the change sets is not particularly efficient. O(N^2)
The library was created with developer efficiency in mind, rather than raw performance. As such, it may not perform well with large data sets.
In my experience, the performance has been perfectly acceptable for data sets with counts in the hundreds. If you plan to use this with larger data sets, you'll want to do some performance testing first and optimize your comparison routine.
I recommend generating the change sets on a background thread.
iOS 6.0+
LMArrayChangeSets is available through CocoaPods. To install it, simply add the following line to your Podfile:
pod "LMArrayChangeSets"
To run the example project, clone the repo, and run pod install from the Example directory first.
cdann, cdann@lintmachine.com
LMArrayChangeSets is available under the MIT license. See the LICENSE file for more info.