---
title: didReorderHandler
framework: uikit
role: symbol
role_heading: Instance Property
path: uikit/uicollectionviewdiffabledatasourcereorderinghandlers/didreorderhandler
---

# didReorderHandler

The handler that processes a reordering transaction.

## Declaration

```occ
@property (nonatomic, copy, nullable) void (^didReorderHandler)(NSDiffableDataSourceTransaction<id,id> *);
```

## Discussion

Discussion The system calls the didReorderHandler handler after a reordering transaction (NSDiffableDataSourceTransaction) occurs, so you can update your data backing store with information about the changes. // Allow every item to be reordered dataSource.reorderingHandlers.canReorderItem = { item in return true }

// Option 1: Update the backing store from a CollectionDifference dataSource.reorderingHandlers.didReorder = { [weak self] transaction in     guard let self = self else { return }          if let updatedBackingStore = self.backingStore.applying(transaction.difference) {         self.backingStore = updatedBackingStore     } }

// Option 2: Update the backing store from the final item identifiers dataSource.reorderingHandlers.didReorder = { [weak self] transaction in     guard let self = self else { return }          self.backingStore = transaction.finalSnapshot.itemIdentifiers }

## See Also

### Reordering items

- [canReorderItemHandler](uikit/uicollectionviewdiffabledatasourcereorderinghandlers/canreorderitemhandler.md)
- [willReorderHandler](uikit/uicollectionviewdiffabledatasourcereorderinghandlers/willreorderhandler.md)