---
title: "activate(on:eventHandler:)"
framework: accessorysetupkit
role: symbol
role_heading: Instance Method
path: "accessorysetupkit/asaccessorysession/activate(on:eventhandler:)"
---

# activate(on:eventHandler:)

Activate the session and start delivering events to an event handler.

## Declaration

```swift
func activate(on queue: dispatch_queue_t, eventHandler: @escaping (ASAccessoryEvent) -> Void)
```

## Parameters

- `queue`: The dispatch the session uses to deliver events to eventHandler.
- `eventHandler`: A closure or block that receives events generated by the session. Each callback to the event handler provides an doc://com.apple.AccessorySetupKit/documentation/AccessorySetupKit/ASAccessoryEvent as a parameter, and expects no return value.

## Mentioned in

Discovering and configuring accessories

## See Also

### Managing the session life cycle

- [invalidate()](accessorysetupkit/asaccessorysession/invalidate().md)