> For the complete documentation index, see [llms.txt](https://developer.magtek.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://developer.magtek.com/sdks-and-tools/universal-sdk-documentation/ios/ieventsubscriber-delegate.md).
# IEventSubscriber Delegate
MTUniversal API will invoke the callback function in this chapter to provide the requested data and/or a detailed response. To delegate the event, call the subscribeAll() function with the name of a class that implements the IEventSubscriber interface.
### OnEvent
OnEvent() handles nearly all event types. The eventType parameter defines which event is triggered.
{% code overflow="wrap" %}
```
(void) OnEvent: (MTU_EventType) eventType
Data: (IData*) data;
```
{% endcode %}
Parameter
Description
eventType
An enumeration indicating the event triggered by the device.
data
Contains the data for the event.
Return Value: None Example:
---
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