How to use AudioKit in SwiftUI? Change state var in view

Question

I have added a listener:

class MIDIReceiver: MIDIListener {
...
}

Where should I put the following code in SwiftUI so that I can use my midi keyboard to change the @State var ?

let midi = MIDI()
midi.openInput()
let receiver = MIDIReceiver()
midi.addListener(receiver)

Thank you

-- Added Oct 28 --

(1) I added the class in https://github.com/AudioKit/Cookbook/blob/main/Cookbook/Cookbook/Recipes/MIDIMonitor.swift but without the view...

After adding @ObservedObject var conductor = MIDIMonitorConductor() in my ContentView, these show in my console.

2020-10-28 00:47:19.646934-0500 AudioKitTrySPM[2998:82471] [midi] MIDI.swift:init():52:Initializing MIDI (MIDI.swift:init():52) 2020-10-28 00:47:19.698885-0500 AudioKitTrySPM[2998:82471] [plugin] AddInstanceForFactory: No factory registered for id <CFUUID 0x600000211300> F8BB1C28-BAE8-11D6-9C31-00039315CD46 2020-10-28 00:47:19.728062-0500 AudioKitTrySPM[2998:82471] HALC_ShellDriverPlugIn::Open: Can't get a pointer to the Open routine

Should I change anything else in the project?

(2) I have an State array in my contentview

    @State private var touchKeys: Array<Bool> = [Bool](repeating: false, count: 24)

How do I trigger a function to map the midi signal to update the array?

Thank you

Answer 1

You can make your receiver ObservableObject and use published properties for values/states you want your SwiftUI view depend/refresh on.

Like in below example:

import Combine

class MIDIReceiver: MIDIListener: ObservableObject {
   @Published var midiSignalReceived = false

   private let midi: MIDI!

   func setup() {
     midi = MIDI()
     midi.openInput()
     midi.addListener(self)
   }

   // ... other code / midi callbacks here
}

// ...

struct ContentView: View {
  @StateObject var midiListener = MIDIListener()

  var body: some View {
     Text("Root View")
       .onReceive(midiListener.$midiSignalReceived) { activated in
           // do something here
       }
       .onAppear {
          self.midiListener.setup()
       }
  }
}

See the example events/states in AudioKit iOS - receivedMIDINoteOn function