Difference of 2 NSArray's for animated insert/delete in UITableView - cocoa-touch

Question

At some point in my Application, I have an NSArray whose contents change. Those contents are shown in a UITableView. I'm trying to find a way to find the diff between the contents of before and after of the NSArray so i can pass the correct indexPaths to insertRowsAtIndexPaths:withRowAnimation: and deleteRowsAtIndexPaths:withRowAnimation: in order to have the changes nicely animated. Any ideas?
thx

Answer 1

Here's is wat i tried and it seems to work, if anyone has anything better, i'd love to see it.
[self.tableView beginUpdates];
NSMutableArray* rowsToDelete = [NSMutableArray array];
NSMutableArray* rowsToInsert = [NSMutableArray array];
for ( NSInteger i = 0; i < oldEntries.count; i++ )
{
FDEntry* entry = [oldEntries objectAtIndex:i];
if ( ! [displayEntries containsObject:entry] )
[rowsToDelete addObject: [NSIndexPath indexPathForRow:i inSection:0]];
}
for ( NSInteger i = 0; i < displayEntries.count; i++ )
{
FDEntry* entry = [displayEntries objectAtIndex:i];
if ( ! [oldEntries containsObject:entry] )
[rowsToInsert addObject: [NSIndexPath indexPathForRow:i inSection:0]];
}
[self.tableView deleteRowsAtIndexPaths:rowsToDelete withRowAnimation:UITableViewRowAnimationFade];
[self.tableView insertRowsAtIndexPaths:rowsToInsert withRowAnimation:UITableViewRowAnimationRight];
[self.tableView endUpdates];

Answer 2

This question from 2010 is what I found when I was googling. Since iOS 5.0, we now also have -[UITableView moveRowAtIndexPath:toIndexPath] which you really want to handle as well. Here is a function that compares two arrays and generates suitable indexpaths for the delete, insert and move operations.
- (void) calculateTableViewChangesBetweenOldArray:(NSArray *)oldObjects
newArray:(NSArray *)newObjects
sectionIndex:(NSInteger)section
indexPathsToDelete:(NSArray **)indexPathsToDelete
indexPathsToInsert:(NSArray **)indexPathsToInsert
indexPathsToMove:(NSArray **)indexPathsToMove
destinationIndexPaths:(NSArray **)destinationIndexPaths
{
NSMutableArray *pathsToDelete = [NSMutableArray new];
NSMutableArray *pathsToInsert = [NSMutableArray new];
NSMutableArray *pathsToMove = [NSMutableArray new];
NSMutableArray *destinationPaths = [NSMutableArray new];
// Deletes and moves
for (NSInteger oldIndex = 0; oldIndex < oldObjects.count; oldIndex++) {
NSObject *object = oldObjects[oldIndex];
NSInteger newIndex = [newObjects indexOfObject:object];
if (newIndex == NSNotFound) {
[pathsToDelete addObject:[NSIndexPath indexPathForRow:oldIndex inSection:section]];
} else if (newIndex != oldIndex) {
[pathsToMove addObject:[NSIndexPath indexPathForRow:oldIndex inSection:section]];
[destinationPaths addObject:[NSIndexPath indexPathForRow:newIndex inSection:section]];
}
}
// Inserts
for (NSInteger newIndex = 0; newIndex < newObjects.count; newIndex++) {
NSObject *object = newObjects[newIndex];
if (![oldObjects containsObject:object]) {
[pathsToInsert addObject:[NSIndexPath indexPathForRow:newIndex inSection:section]];
}
}
if (indexPathsToDelete) *indexPathsToDelete = [pathsToDelete copy];
if (indexPathsToInsert) *indexPathsToInsert = [pathsToInsert copy];
if (indexPathsToMove) *indexPathsToMove = [pathsToMove copy];
if (destinationIndexPaths) *destinationIndexPaths = [destinationPaths copy];
}
An example on how to use it. Assume you're displaying a table of people, which you keep in the array self.people. The section index where the people are displayed is 0.
- (void) setPeople:(NSArray <Person *> *)newPeople {
dispatch_async(dispatch_get_main_queue(), ^{
[self.tableView beginUpdates];
NSArray *rowsToDelete, *rowsToInsert, *rowsToMove, *destinationRows;
[self calculateTableViewChangesBetweenOldArray:self.people
newArray:newPeople
sectionIndex:0
indexPathsToDelete:&rowsToDelete
indexPathsToInsert:&rowsToInsert
indexPathsToMove:&rowsToMove
destinationIndexPaths:&destinationRows
];
self.people = newPeople;
[self.tableView deleteRowsAtIndexPaths:rowsToDelete withRowAnimation:UITableViewRowAnimationFade];
[self.tableView insertRowsAtIndexPaths:rowsToInsert withRowAnimation:UITableViewRowAnimationFade];
[rowsToMove enumerateObjectsUsingBlock:^(NSIndexPath * _Nonnull oldIndexPath, NSUInteger idx, BOOL * _Nonnull stop) {
NSIndexPath *newIndexPath = destinationRows[idx];
[self.tableView moveRowAtIndexPath:oldIndexPath toIndexPath:newIndexPath];
}];
[self.tableView endUpdates];
});
}