June 10, 2015 Gene De Lisa 21 Comments

Swift 2 and CoreMIDI

Swift 1.2 is notorious regarding its lack of function pointers to deal with C APIs such as Core MIDI. I’ve complained^H^H^H^H^H written about this several times.

Introduction
MIDI Client
Input Port
Virtual Destination
Summary
Resources

Introduction

Well, praise Zeus, Thor, and the FSM, in Swift 2 beta, Core MIDI is easier to use without function pointers or trampolines.

MIDI Client

Table of Contents

The first step in using CoreMIDI is to create a MIDIClient reference. To do that, you use MIDIClientCreate() which takes a function pointer among other parameters. That is the problem. Swift 1.2 barfs on C function pointers.

The solution in Swift 2 (beta) is the introduction of MIDIClientCreateWithBlock() which will take a closure of type MIDINotifyBlock. This is quite similar to the Objective-C trampoline (but without the Objective-C). Take a look at the naming in my old trampoline code and tell me I’m not a mind reader 🙂

var status = OSStatus(noErr)
var midiClient = MIDIClientRef()
status = MIDIClientCreateWithBlock("MyMIDIClient", &midiClient, MyMIDINotifyBlock)

//typealias MIDINotifyBlock = (UnsafePointer<MIDINotification>) -> Void
func MyMIDINotifyBlock(midiNotification: UnsafePointer<MIDINotification>) {
}

var status = OSStatus(noErr)

var midiClient = MIDIClientRef()

status = MIDIClientCreateWithBlock("MyMIDIClient", &midiClient, MyMIDINotifyBlock)

//typealias MIDINotifyBlock = (UnsafePointer<MIDINotification>) -> Void

func MyMIDINotifyBlock(midiNotification: UnsafePointer<MIDINotification>) {

}

Groovy.
Well, sort of.
What are you going to do with that MIDINotification?

The different types of notifications are different unrelated structures.

struct MIDINotification {
    var messageID: MIDINotificationMessageID
    var messageSize: UInt32
}
struct MIDIObjectAddRemoveNotification { 
    var messageID: MIDINotificationMessageID
    var messageSize: UInt32
    var parent: MIDIObjectRef
    var parentType: MIDIObjectType
    var child: MIDIObjectRef
    var childType: MIDIObjectType
}

struct MIDINotification {

var messageID: MIDINotificationMessageID

var messageSize: UInt32

}

struct MIDIObjectAddRemoveNotification {

var messageID: MIDINotificationMessageID

var messageSize: UInt32

var parent: MIDIObjectRef

var parentType: MIDIObjectType

var child: MIDIObjectRef

var childType: MIDIObjectType

}

You cannot downcast these via as?

Previously, I simply used unsafeBitCast. That does not work anymore directly. You need to use withUnsafePointer like this:

func MyMIDINotifyBlock(midiNotification: UnsafePointer<MIDINotification>) {
    let notification = midiNotification.memory
    switch (notification.messageID) {
        case .MsgObjectAdded:
            // has to be a var
            var mem = midiNotification.memory
            withUnsafePointer(&mem) { ptr -> Void in
                let mp = unsafeBitCast(ptr, UnsafePointer<MIDIObjectAddRemoveNotification>.self)
                let m = mp.memory
                print("id \(m.messageID)")
                print("size \(m.messageSize)")
                print("child \(m.child)")
                print("child type \(m.childType)")
                print("parent \(m.parent)")
                print("parentType \(m.parentType)")
            }
etc.

func MyMIDINotifyBlock(midiNotification: UnsafePointer<MIDINotification>) {

let notification = midiNotification.memory

switch (notification.messageID) {

case .MsgObjectAdded:

// has to be a var

var mem = midiNotification.memory

withUnsafePointer(&mem) { ptr -> Void in

let mp = unsafeBitCast(ptr, UnsafePointer<MIDIObjectAddRemoveNotification>.self)

let m = mp.memory

print("id \(m.messageID)")

print("size \(m.messageSize)")

print("child \(m.child)")

print("child type \(m.childType)")

print("parent \(m.parent)")

print("parentType \(m.parentType)")

}

etc.

Yeah, I know.
Gross.
But it works.

By the way, MIDIClientCreate has been updated too as well as the definitions of the callbacks.

let np:MIDINotifyProc = { (notification:UnsafePointer<MIDINotification>, refcon:UnsafeMutablePointer<Void>) in
}
status = MIDIClientCreate("MyMIDIClient", np, nil, &midiClient)

let np:MIDINotifyProc = { (notification:UnsafePointer<MIDINotification>, refcon:UnsafeMutablePointer<Void>) in

}

status = MIDIClientCreate("MyMIDIClient", np, nil, &midiClient)

Input Port

Table of Contents

Similarly, MIDIInputPortCreate() which also takes a function pointer (to a read proc) has been upgraded to MIDIInputPortCreateWithBlock() which will take a MIDIReadBlock.

var inputPort = MIDIPortRef()
status = MIDIInputPortCreateWithBlock(midiClient, "MyClient In", &inputPort, MyMIDIReadBlock)
// check status

var inputPort = MIDIPortRef()

status = MIDIInputPortCreateWithBlock(midiClient, "MyClient In", &inputPort, MyMIDIReadBlock)

// check status

And the read block:

//typealias MIDIReadBlock = (UnsafePointer<MIDIPacketList>, UnsafeMutablePointer<Void>) -> Void

func MyMIDIReadBlock(packetList: UnsafePointer<MIDIPacketList>, srcConnRefCon: UnsafeMutablePointer<Void>) -> Void {
    let packets = packetList.memory
    let packet:MIDIPacket = packets.packet.0
    var ap = UnsafeMutablePointer<MIDIPacket>.alloc(1)
    ap.initialize(packet)
        
    for _ in 0 ..< packets.numPackets {
        let p = ap.memory
        handle(p)
        ap = MIDIPacketNext(ap)
    }        
}

func handle(packet:MIDIPacket) {
blah blah

//typealias MIDIReadBlock = (UnsafePointer<MIDIPacketList>, UnsafeMutablePointer<Void>) -> Void

func MyMIDIReadBlock(packetList: UnsafePointer<MIDIPacketList>, srcConnRefCon: UnsafeMutablePointer<Void>) -> Void {

let packets = packetList.memory

let packet:MIDIPacket = packets.packet.0

var ap = UnsafeMutablePointer<MIDIPacket>.alloc(1)

ap.initialize(packet)

for _ in 0 ..< packets.numPackets {

let p = ap.memory

handle(p)

ap = MIDIPacketNext(ap)

}

func handle(packet:MIDIPacket) {

blah blah

As you can see, iterating trough the packets has not been changed much. Swift does have MIDIPacketNext now though. It was MIA previously.

Personally, I think that if it were a SequenceType it would be much easier. You could do this:

for packet in packets {

1	for packet in packets {

Dream on.

Instead, you have to do some pointer nonsense. And the packets are a tuple, not an array. This example is one way to navigate the list. If you have something more elegant, let me know.

MIDIInputPortCreate() and the read function have also been updated in Swift 2 beta.

Virtual Destination

Table of Contents

To create a Virtual Destination, there is now MIDIDestinationCreateWithBlock() which also takes a MIDIReadBlock.

var destEndpointRef = MIDIEndpointRef()

status = MIDIDestinationCreateWithBlock(midiClient,
                "Virtual Dest",
                &destEndpointRef,
                readBlock)

var destEndpointRef = MIDIEndpointRef()

status = MIDIDestinationCreateWithBlock(midiClient,

"Virtual Dest",

&destEndpointRef,

readBlock)

Remember that you have to edit your Info.plist and add the key “Required Background Modes” with the value set to audio (It will say “App plays audio or streams audio/video using AirPlay”) to create virtual destinations.

Summary

Table of Contents

Several new CoreMIDI functions have been added to Swift 2 beta. Here they are:

MIDIClientCreateWithBlock()
MIDIInputPortCreateWithBlock()
MIDIDestinationCreateWithBlock()
MIDIReadBlock
MIDINotifyBlock
MIDIPacketNext()

As always, there is my complete working example project on Github.

Have fun.

Resources

Table of Contents

Github project

Objective-C Trampoline

Swift and C API callbacks

CoreMIDI changes in iOS 9

MIDI Swift

21 thoughts on “Swift 2 and CoreMIDI”

Pingback: Swift 2 and CoreMIDI | Dinesh Ram Kali.

Hi Gene,

thank you for the informative articles regarding MIDI and swift. I am very new to OS X programming and Swift, and was going through your website trying to put together the pieces of the puzzle. I wanted to see if I could write a little playground test to read input from my midi keyboard. The code I have written below however seems to have trouble connecting the source to the input port (MIDIPortConnectSource returns status -50).

I also noticed that the “*WithBlock” functions are only available in OS X 10.11, I was not able to use them until I installed the beta.

Below is my short playground, if you or anyone else has any suggestions they would be appreciated.

import Cocoa
import CoreMIDI

var status = OSStatus(noErr)

func MyMIDINotifyBlock(midiNotification: UnsafePointer)
{
    print("received notification");
}

func MyMIDIReadBlock(packetList: UnsafePointer, srcConnRefCon: UnsafeMutablePointer) -> Void {
    print("received packet");
}


//create MIDI client
var midiClient = MIDIClientRef()
status = MIDIClientCreateWithBlock("MyMIDIClient", &midiClient, MyMIDINotifyBlock)
if status == OSStatus(noErr) {
    print("Client created successfully")
} else {
    print("Error creating MIDI client. Error code: \(status.description)")
}


//create MIDI port
var inputPort = MIDIPortRef()
status = MIDIInputPortCreateWithBlock(midiClient, "MyMIDIClientInputPort", &inputPort, MyMIDIReadBlock)
if status == OSStatus(noErr) {
    print("Input port created successfully")
} else {
    print("Error creating MIDI input port. Error code: \(status.description)")
}


let numSrcs = MIDIGetNumberOfSources()
print("Number sources: \(numSrcs)")

var midiEndpoint = MIDIGetSource(1)


//connect source MIDI endpoint to the input port
status = MIDIPortConnectSource   (inputPort, midiEndpoint,nil )
if status == OSStatus(noErr) {
    print("Successfully connected to \(midiEndpoint)")
} else {
    print("Failed to establish connection. Error code: \(status.description)")
}

import Cocoa

import CoreMIDI

var status = OSStatus(noErr)

func MyMIDINotifyBlock(midiNotification: UnsafePointer)

{

print("received notification");

}

func MyMIDIReadBlock(packetList: UnsafePointer, srcConnRefCon: UnsafeMutablePointer) -> Void {

print("received packet");

}

//create MIDI client

var midiClient = MIDIClientRef()

status = MIDIClientCreateWithBlock("MyMIDIClient", &midiClient, MyMIDINotifyBlock)

if status == OSStatus(noErr) {

print("Client created successfully")

} else {

print("Error creating MIDI client. Error code: \(status.description)")

}

//create MIDI port

var inputPort = MIDIPortRef()

status = MIDIInputPortCreateWithBlock(midiClient, "MyMIDIClientInputPort", &inputPort, MyMIDIReadBlock)

if status == OSStatus(noErr) {

print("Input port created successfully")

} else {

print("Error creating MIDI input port. Error code: \(status.description)")

}

let numSrcs = MIDIGetNumberOfSources()

print("Number sources: \(numSrcs)")

var midiEndpoint = MIDIGetSource(1)

//connect source MIDI endpoint to the input port

status = MIDIPortConnectSource (inputPort, midiEndpoint,nil )

if status == OSStatus(noErr) {

print("Successfully connected to \(midiEndpoint)")

} else {

print("Failed to establish connection. Error code: \(status.description)")

}

Alex says:

August 2, 2015 at 7:09 pm

…there was only one device plugged in I should have known this…

changing the hardcoded source from 1 to 0 solved the problem:
var midiEndpoint = MIDIGetSource(0)

I am now able to receive packets.

thanks again for all your great articles

Reply
1. Gene De Lisa says:
  
  August 3, 2015 at 2:56 pm
  
  In real life you’d use something like NSPopUpButtons to present the user with a menu of sources/destinations to connect.
  
  Glad you got your example working!
  
  Reply

Gene, many thanks on your notes and project. Very helpful. One thing I found. If you have a complex MIDI message coming back in the read block (say sysex) and don’t want the tuples, you can do:

let pktMirror = Mirror(reflecting: packet.data)
var midiData: [UInt8] = []
for child in pktMirror.children {
        midiData.append((child.value as? UInt8)!)
}

// And then:

    let header = midiData[0...4]
    let deviceid = midiData[5...11]

let pktMirror = Mirror(reflecting: packet.data)

var midiData: [UInt8] = []

for child in pktMirror.children {

midiData.append((child.value as? UInt8)!)

}

// And then:

let header = midiData[0...4]

let deviceid = midiData[5...11]

Jess Hendricks says:

November 3, 2015 at 7:21 pm

Hi Gene,

I was wondering if you have been able to parse out the values of the data in MIDIMetaEvent? I am only able to get the numerator of a time signature, but I desperately need the rest of the data for a project I am working on. It says that data is of the type (UInt8). As best I can tell, that means that its supposed to be a tuple, but nothing I do seems to imply I can access other values. The dataLength is correct and returns ’04’, suggesting the four bytes for a time signature event. Additionally CAShow displays the proper time signature.

Reply
1. Gene De Lisa says:
  
  November 5, 2015 at 11:38 am
  
  Wouldn’t that be nice! MIDIMetaEvent is a mess with that tuple nonsense.
  You can use Mirror on the data, iterate over it, and copy it into an array.
  But what a PITA. Apple needs to update this.
  
  Reply
  1. Jess Hendricks says:
    
    November 20, 2015 at 9:41 am
    
    Cool, thanks!
    
    Reply
  2. Jess Hendricks says:
    
    November 21, 2015 at 11:40 am
    
    By the way, if you happen to know where I can find an example of how this is done, it would be very helpful. I have noticed that it is also an issue with getting the instrument and track names.
    
    Reply
Cater says:

December 11, 2015 at 2:39 am

Hi Gene,
This is a pretty fantastic post for me, and now my app can receive note from my keyboard(via USB camera adapter) and everything seems fine.
However, now I want to sent note to my keyboard device from my iPad, is that possible? my keyboard has a separate speaker so it can play the sound my itself.
Any information will be appreciate.
Thanks!

Reply
1. Cater says:
  
  December 14, 2015 at 9:26 pm
  
  Thanks, I read the official document for some times and get the solution.
  Finally I init a new midi client and use
  func MIDISend(port: MIDIPortRef, _ dest: MIDIEndpointRef, _ pktlist: UnsafePointer) -> OSStatus
  to sent data to my destination port
  everything looks good now~
  Best wishes
  By Cater
  
  Reply

Hey Gene, thanks for the great posts.
I am running Swift 2.1.1 and I tried out the UnsafePointer code you have above for casting MIDINotification to
MIDIObjectAddRemoveNotification. While there were no errors the fields beyond the messageID were invalid.

The code below works in Swift 2.1.1 …
MIDIClientCreate("MidiTestClient", TestMIDINotifyProc,nil, &midiClient);

func TestMIDINotifyProc(message: UnsafePointer, refCon: UnsafeMutablePointer) -> Void { let notification:MIDINotification = message.memory;

if (notification.messageID == .MsgObjectAdded || notification.messageID == .MsgObjectRemoved) { let msgPtr:UnsafePointer = UnsafePointer(message); let changeMsg:MIDIObjectAddRemoveNotification = msgPtr.memory; } }

Sorry I did put code tags around the code but the template characters were stripped anyway.
All of the UnsafePointer code in the example should have had the types in them. i.e. MIDINotification and MIDIObjectAddRemoveNotification.

Regards,
Matt

Gotta love WordPress. Maybe the pre tag is the way to go.

Let me try it:

func MyMIDINotifyBlock(midiNotification: UnsafePointer<MIDINotification>) {

1	func MyMIDINotifyBlock(midiNotification: UnsafePointer<MIDINotification>) {

So yeah, the pre tag works better than the code tag.

OK here it is with pre tags

func TestMIDINotifyProc(message: UnsafePointer, refCon: UnsafeMutablePointer) -> Void
{
    let notification:MIDINotification = message.memory;
    
    if (notification.messageID == .MsgObjectAdded || notification.messageID == .MsgObjectRemoved)
    {
        let msgPtr:UnsafePointer = UnsafePointer(message);
        let changeMsg:MIDIObjectAddRemoveNotification = msgPtr.memory;
        ...
     }
}

func TestMIDINotifyProc(message: UnsafePointer, refCon: UnsafeMutablePointer) -> Void

{

let notification:MIDINotification = message.memory;

if (notification.messageID == .MsgObjectAdded || notification.messageID == .MsgObjectRemoved)

{

let msgPtr:UnsafePointer = UnsafePointer(message);

let changeMsg:MIDIObjectAddRemoveNotification = msgPtr.memory;

...

}

Thanks again.

Gene De Lisa says:

January 1, 2016 at 12:23 pm

I haven’t looked at the pointer frobs since beta. Thanks for the head’s up; I’ll take a look.

Reply

Luke Bartolomeo says:

May 26, 2016 at 2:48 pm

Unfortunately MIDIClientCreateWithBlock is only available in iOS 9+, regardless of what version of Swift you are using.

Reply
1. Gene De Lisa says:
  
  June 1, 2016 at 10:48 am
  
  Yup. You have to dance the trampoline chacha before 9.
  
  Reply
Sven says:

November 20, 2017 at 8:25 am

I wrote a simple MIDI app that is also supposed to capture MIDI while running in the background.
However, just adding the „audio“ key to background modes in Info.plist doesn’t seem to do it in iOS 11.
When I put the app into background by pressing the Home button, the midiReadProc callback is not invoked anymore when I send MIDI.
I also tried to start an AVAudioSession and start an AVAudioEngine with a dummy AVAudioUnitSampler but no luck.
Any helpful hints on this?

Reply
1. Gene De Lisa says:
  
  November 30, 2017 at 9:17 am
  
  are you connecting to your app via a virtual midi connection?
  
  Reply

Swift 2 and CoreMIDI

Swift 2 and CoreMIDI

Introduction

MIDI Client

Input Port

Virtual Destination

Summary

Resources

21 thoughts on “Swift 2 and CoreMIDI”

Leave a Reply Cancel reply

Enjoy this blog? Please spread the word :)

Swift 2 and CoreMIDI

Swift 2 and CoreMIDI

Introduction

MIDI Client

Input Port

Virtual Destination

Summary

Resources

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21 thoughts on “Swift 2 and CoreMIDI”

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Enjoy this blog? Please spread the word :)