accessorysetupkit

# AccessorySetupKit

Use the iOS 18+ system picker for privacy-preserving Bluetooth/Wi-Fi accessory
discovery and authorization, then hand off communication to CoreBluetooth or
NetworkExtension.

## Contents

- [Setup and Entitlements](#setup-and-entitlements)
- [Discovery Descriptors](#discovery-descriptors)
- [Presenting the Picker](#presenting-the-picker)
- [Event Handling](#event-handling)
- [Bluetooth Accessories](#bluetooth-accessories)
- [Wi-Fi Accessories](#wi-fi-accessories)
- [Migration from CoreBluetooth](#migration-from-corebluetooth)
- [Common Mistakes](#common-mistakes)
- [Review Checklist](#review-checklist)
- [References](#references)

## Setup and Entitlements

### Info.plist Configuration

Add these keys to the app's Info.plist:

| Key | Type | Purpose |
|---|---|---|
| `NSAccessorySetupSupports` | `[String]` | Required. Array containing `Bluetooth` and/or `WiFi` |
| `NSAccessorySetupBluetoothServices` | `[String]` | Service UUIDs the app discovers (Bluetooth) |
| `NSAccessorySetupBluetoothNames` | `[String]` | Bluetooth names or substrings to match |
| `NSAccessorySetupBluetoothCompanyIdentifiers` | `[String]` | Two-byte Bluetooth company identifiers |

The Bluetooth-specific keys must match the values used in `ASDiscoveryDescriptor`.
If the app uses identifiers, names, or services not declared in Info.plist, the
app crashes during AccessorySetupKit discovery. For Wi-Fi accessories, include
`WiFi` in `NSAccessorySetupSupports` and match the descriptor's SSID rule.

### No Bluetooth Permission Required

When an app declares `NSAccessorySetupSupports` with `Bluetooth`, creating a
`CBCentralManager` no longer triggers the system Bluetooth permission dialog.
The central manager's state transitions to `poweredOn` only when the app has
at least one paired accessory via AccessorySetupKit.

## Discovery Descriptors

`ASDiscoveryDescriptor` defines the matching criteria for finding accessories.
The system matches scanned results against all rules in the descriptor to
filter for the target accessory.

### Bluetooth Descriptor

```swift
import AccessorySetupKit
import CoreBluetooth

var descriptor = ASDiscoveryDescriptor()
descriptor.bluetoothServiceUUID = CBUUID(string: "12345678-1234-1234-1234-123456789ABC")
descriptor.bluetoothNameSubstring = "MyDevice"
descriptor.bluetoothRange = .immediate  // Only nearby devices
```

A Bluetooth descriptor needs at least one of `bluetoothCompanyIdentifier` or
`bluetoothServiceUUID`. Add narrower matchers as needed:

- `bluetoothNameSubstring` with a company identifier or service UUID
- `bluetoothManufacturerDataBlob` and `bluetoothManufacturerDataMask` with a
  company identifier; blob and mask must have the same length
- `bluetoothServiceDataBlob` and `bluetoothServiceDataMask` with a service UUID;
  blob and mask must have the same length

### Wi-Fi Descriptor

```swift
var descriptor = ASDiscoveryDescriptor()
descriptor.ssid = "MyAccessory-Network"
// OR use a prefix:
// descriptor.ssidPrefix = "MyAccessory-"
```

Supply either `ssid` or `ssidPrefix`, not both. The app crashes if both are set.
The `ssidPrefix` must have a non-zero length.

### Bluetooth Range

Control the physical proximity required for discovery:

| Value | Behavior |
|---|---|
| `.default` | Standard Bluetooth range |
| `.immediate` | Only accessories in close physical proximity |

### Support Options

Set `supportedOptions` on the descriptor to declare the accessory's capabilities:

```swift
descriptor.supportedOptions = [.bluetoothPairingLE, .bluetoothTransportBridging]
```

| Option | Purpose |
|---|---|
| `.bluetoothPairingLE` | BLE pairing support |
| `.bluetoothTransportBridging` | Bluetooth transport bridging |
| `.bluetoothHID` | Bluetooth HID device |

## Presenting the Picker

### Creating the Session

Create and activate an `ASAccessorySession` to manage discovery lifecycle. Wait for `.activated` before reading `session.accessories` or presenting the picker:

```swift
import AccessorySetupKit

final class AccessoryManager {
    private let session = ASAccessorySession()

    func start() {
        session.activate(on: .main) { [weak self] event in
            self?.handleEvent(event)
        }
    }

    private func handleEvent(_ event: ASAccessoryEvent) {
        switch event.eventType {
        case .activated:
            // Session ready. Check session.accessories for previously paired devices.
            break
        case .accessoryAdded:
            guard let accessory = event.accessory else { return }
            handleAccessoryAdded(accessory)
        case .accessoryChanged:
            // Accessory properties changed (e.g., display name updated in Settings)
            break
        case .accessoryRemoved:
            // Accessory removed by user or app
            break
        case .invalidated:
            // Session invalidated, cannot be reused
            break
        @unknown default:
            break
        }
    }
}
```

### Showing the Picker

Create `ASPickerDisplayItem` instances with a name, product image, and
discovery descriptor, then pass them to the activated session:

```swift
func showAccessoryPicker() {
    var descriptor = ASDiscoveryDescriptor()
    descriptor.bluetoothServiceUUID = CBUUID(string: "ABCD1234-0000-1000-8000-00805F9B34FB")

    guard let image = UIImage(named: "my-accessory") else { return }

    let item = ASPickerDisplayItem(
        name: "My Bluetooth Accessory",
        productImage: image,
        descriptor: descriptor
    )

    session.showPicker(for: [item]) { error in
        if let error {
            print("Picker failed: \(error.localizedDescription)")
        }
    }
}
```

The picker runs in a separate system process. It shows each matching device
as a separate item. When multiple devices match a given descriptor, the picker
creates a horizontal carousel.

### Setup Options

Configure picker behavior per display item:

```swift
var item = ASPickerDisplayItem(
    name: "My Accessory",
    pr