# CKSyncEngineDelegate An interface for providing record data to a sync engine and customizing that engine’s behavior. ``` @protocol CKSyncEngineDelegate ``` ## Overview> Important: ``doc://com.apple.cloudkit/documentation/CloudKit/CKSyncEngine-4b4w9`` delivers events serially, which means the delegate doesn’t receive the next event until it finishes handling the current one. > To maintain this ordering, don’t call sync engine methods from your delegate that may cause the engine to generate additional events. > For example, don’t invoke ``doc://com.apple.cloudkit/documentation/CloudKit/CKSyncEngine-4b4w9/fetchChangesWithCompletionHandler:`` or ``doc://com.apple.cloudkit/documentation/CloudKit/CKSyncEngine-4b4w9/sendChangesWithCompletionHandler:`` from within ``doc://com.apple.cloudkit/documentation/CloudKit/CKSyncEngineDelegate-3c38p/syncEngine:handleEvent:``. ## Topics ### Handling sync events [`syncEngine:handleEvent:`](/documentation/CloudKit/CKSyncEngineDelegate-3c38p/syncEngine:handleEvent:) Tells the delegate to handle the specified sync event. [`CKSyncEngineEvent`](/documentation/CloudKit/CKSyncEngineEvent) An event that occurs during a sync operation. ### Sending changes [`syncEngine:nextRecordZoneChangeBatchForContext:`](/documentation/CloudKit/CKSyncEngineDelegate-3c38p/syncEngine:nextRecordZoneChangeBatchForContext:) Asks the delegate to provide the next set of record changes to send to the server. [`CKSyncEngineSendChangesContext`](/documentation/CloudKit/CKSyncEngineSendChangesContext) The context of an attempt to send changes to the server. [`CKSyncEngineRecordZoneChangeBatch`](/documentation/CloudKit/CKSyncEngineRecordZoneChangeBatch) An object that contains the record changes for a single send operation. --- Copyright © 2026 Apple Inc. All rights reserved. | [Terms of Use](https://www.apple.com/legal/internet-services/terms/site.html) | [Privacy Policy](https://www.apple.com/privacy/privacy-policy)