---
title: IOServiceInterestCallback
framework: iokit
role: symbol
role_heading: Type Alias
path: iokit/ioserviceinterestcallback
---

# IOServiceInterestCallback

Callback function to be notified of changes in state of an IOService.

## Declaration

```swift
typealias IOServiceInterestCallback = (UnsafeMutableRawPointer?, io_service_t, UInt32, UnsafeMutableRawPointer?) -> Void
```

## Parameters

- `refcon`: The refcon passed when the notification was installed.
- `service`: The IOService whose state has changed.
- `messageType`: A messageType enum, defined by IOKit/IOMessage.h or by the IOService's family.
- `messageArgument`: An argument for the message, dependent on the messageType. If the message data is larger than sizeof(void*), then messageArgument contains a pointer to the message data; otherwise, messageArgument contains the message data.

## See Also

### Callbacks

- [IOAsyncCallback](iokit/ioasynccallback.md)
- [IOAsyncCallback0](iokit/ioasynccallback0.md)
- [IOAsyncCallback1](iokit/ioasynccallback1.md)
- [IOAsyncCallback2](iokit/ioasynccallback2.md)
- [IOServiceMatchingCallback](iokit/ioservicematchingcallback.md)