在iOS设备上，可以使用ExternalAccessory框架来实现设备作为外设的功能。但是，安卓设备无法直接检测到iOS设备作为外设。但可以通过使用蓝牙或Wi-Fi等通信方式来实现iOS设备与安卓设备之间的通信。

以下是一个简单的示例代码，演示了如何在iOS设备上作为外设，并通过蓝牙与安卓设备进行通信。

在iOS设备上创建一个外设（Peripheral）：

import CoreBluetooth

class PeripheralManager: NSObject, CBPeripheralManagerDelegate {
    private var peripheralManager: CBPeripheralManager!
    private var characteristic: CBMutableCharacteristic!

    override init() {
        super.init()
        peripheralManager = CBPeripheralManager(delegate: self, queue: nil)
    }

    func peripheralManagerDidUpdateState(_ peripheral: CBPeripheralManager) {
        if peripheral.state == .poweredOn {
            let serviceUUID = CBUUID(string: "YOUR_SERVICE_UUID")
            let characteristicUUID = CBUUID(string: "YOUR_CHARACTERISTIC_UUID")
            let service = CBMutableService(type: serviceUUID, primary: true)

            characteristic = CBMutableCharacteristic(type: characteristicUUID, properties: [.read, .write], value: nil, permissions: [.readable, .writeable])

            service.characteristics = [characteristic]

            peripheralManager.add(service)
            peripheralManager.startAdvertising([CBAdvertisementDataServiceUUIDsKey: [serviceUUID]])
        }
    }

    func peripheralManager(_ peripheral: CBPeripheralManager, didReceiveWrite requests: [CBATTRequest]) {
        for request in requests {
            if let value = request.value {
                let stringValue = String(data: value, encoding: .utf8)
                print("Received value: \(stringValue ?? "")")
            }

            peripheralManager.respond(to: request, withResult: .success)
        }
    }
}

在安卓设备上，通过蓝牙与iOS设备进行通信：

import android.bluetooth.BluetoothAdapter
import android.bluetooth.BluetoothDevice
import android.bluetooth.BluetoothSocket

import java.io.IOException
import java.util.*

class BluetoothClient {
    private val bluetoothAdapter: BluetoothAdapter? = BluetoothAdapter.getDefaultAdapter()
    private val deviceAddress = "YOUR_IOS_DEVICE_ADDRESS"
    private val uuid = UUID.fromString("YOUR_SERVICE_UUID")
    private var socket: BluetoothSocket? = null

    fun connect() {
        val device: BluetoothDevice? = bluetoothAdapter?.getRemoteDevice(deviceAddress)

        try {
            socket = device?.createRfcommSocketToServiceRecord(uuid)
            socket?.connect()
        } catch (e: IOException) {
            e.printStackTrace()
        }
    }

    fun send(data: String) {
        val outputStream = socket?.outputStream

        try {
            outputStream?.write(data.toByteArray())
        } catch (e: IOException) {
            e.printStackTrace()
        }
    }

    fun disconnect() {
        try {
            socket?.close()
        } catch (e: IOException) {
            e.printStackTrace()
        }
    }
}

请注意，上述代码只是一个简单的示例，并且需要根据你的具体需求进行修改和完善。