# MIDIClientCreateWithBlock(_:_:_:) Creates a MIDI client with a callback block. ``` func MIDIClientCreateWithBlock(_ name: CFString, _ outClient: UnsafeMutablePointer, _ notifyBlock: MIDINotifyBlock?) -> OSStatus ``` ## Parameters `name` The client’s name. `outClient` On successful return, points to the newly created MIDI client. `notifyBlock` An optional block on which the client receives notifications of changes to the system. This system calls this block on an arbitrary thread. Thread-safety is the block’s responsibility. ## Return Value An `OSStatus` result code. ## Topics ### Callbacks [`MIDINotifyBlock`](/documentation/CoreMIDI/MIDINotifyBlock) A callback block for notifying clients of state changes. [`MIDINotification`](/documentation/CoreMIDI/MIDINotification) A message that describes a system state change. --- Copyright © 2026 Apple Inc. All rights reserved. | [Terms of Use](https://www.apple.com/legal/internet-services/terms/site.html) | [Privacy Policy](https://www.apple.com/privacy/privacy-policy)