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# CKSyncEngineDelegate

An interface for providing record data to a sync engine and customizing that engine’s behavior.

```
protocol CKSyncEngineDelegate : AnyObject, Sendable
```

## Overview> Important: ``doc://com.apple.cloudkit/documentation/CloudKit/CKSyncEngine-5sie5`` 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-5sie5/fetchChanges(_:)`` or ``doc://com.apple.cloudkit/documentation/CloudKit/CKSyncEngine-5sie5/sendChanges(_:)`` from within ``doc://com.apple.cloudkit/documentation/CloudKit/CKSyncEngineDelegate-1q7g8/handleEvent(_:syncEngine:)``.

## Topics

### Handling sync events

[`handleEvent(_:syncEngine:)`](/documentation/CloudKit/CKSyncEngineDelegate-1q7g8/handleEvent(_:syncEngine:))

Tells the delegate to handle the specified sync event.

[`CKSyncEngine.Event`](/documentation/CloudKit/CKSyncEngine-5sie5/Event)

Describes an event that occurs during a sync operation.

[`CKSyncEngineEventType`](/documentation/CloudKit/CKSyncEngineEventType)

Describes an event that occurs during a sync operation.

### Sending changes

[`nextRecordZoneChangeBatch(_:syncEngine:)`](/documentation/CloudKit/CKSyncEngineDelegate-1q7g8/nextRecordZoneChangeBatch(_:syncEngine:))

Asks the delegate to provide the next set of record changes to send to the server.

[`CKSyncEngine.SendChangesContext`](/documentation/CloudKit/CKSyncEngine-5sie5/SendChangesContext)

The context of an attempt to send changes to the server.

[`CKSyncEngine.RecordZoneChangeBatch`](/documentation/CloudKit/CKSyncEngine-5sie5/RecordZoneChangeBatch)

A type that contains the record changes for a single send operation.


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