---
title: MIDINotifyBlock
framework: coremidi
role: symbol
role_heading: Type Alias
path: coremidi/midinotifyblock
---

# MIDINotifyBlock

A callback block for notifying clients of state changes.

## Declaration

```swift
typealias MIDINotifyBlock = (UnsafePointer<MIDINotification>) -> Void
```

## Parameters

- `message`: A structure that contains information about what changed.

## Discussion

Discussion The system calls this block when some aspect of the current MIDI setup changes. The system calls it on an arbitrary thread chosen by the implementation; thread safety is the responsibility of the block.

## See Also

### Callbacks

- [MIDINotification](coremidi/midinotification.md)