I have a very cheap Bluetooth-connected printer. And I want to print out a word or two via Core Bluetooth. It's an iOS app with the SwiftUI framework. The following is what I have for an ObservableObject class.
import Foundation
import CoreBluetooth
class BluetoothManager: NSObject, ObservableObject, CBCentralManagerDelegate, CBPeripheralDelegate {
@Published var connectedDevices: [CBPeripheral] = []
@Published var powerOn = false
@Published var peripheralConnected = false
private var centralManager: CBCentralManager!
private var peripheralName = "LX-D02"
private var connectedPeripheral: CBPeripheral?
private var writeCharacteristic: CBCharacteristic?
private let serviceUUID = CBUUID(string:"5833FF01-9B8B-5191-6142-22A4536EF123")
private let characteristicUUID = CBUUID(string: "FFE1")
override init() {
super.init()
self.centralManager = CBCentralManager(delegate: self, queue: nil)
}
func startScanning() {
if centralManager.state == .poweredOn {
centralManager.scanForPeripherals(withServices: nil, options: nil)
}
}
func centralManagerDidUpdateState(_ central: CBCentralManager) {
if central.state == .poweredOn {
powerOn = true
print("Bluetooth is powered on")
} else {
print("Bluetooth is not available")
}
}
func centralManager(_ central: CBCentralManager, didDiscover peripheral: CBPeripheral, advertisementData: [String : Any], rssi RSSI: NSNumber) {
if !connectedDevices.contains(peripheral) {
if let localName = advertisementData["kCBAdvDataLocalName"] as? String {
if localName == peripheralName {
connectedDevices.append(peripheral)
centralManager.connect(peripheral, options: nil)
centralManager.stopScan()
peripheralConnected = true
print("Connected: \(peripheral.identifier.uuidString)")
}
}
}
}
func centralManager(_ central: CBCentralManager, didConnect peripheral: CBPeripheral) {
connectedPeripheral = peripheral
peripheral.delegate = self
let services = [serviceUUID]
peripheral.discoverServices(services)
//discoverServices(peripheral: peripheral)
}
func centralManager(_ central: CBCentralManager, didFailToConnect peripheral: CBPeripheral, error: (any Error)?) {
guard let error = error else {
print("Failed connection unobserved")
return
}
print("Error: \(error.localizedDescription)")
}
func peripheral(_ peripheral: CBPeripheral, didDiscoverServices error: Error?) {
if let error = error {
print("Failing to discover servies: \(error.localizedDescription)")
return
}
discoverCharacteristics(peripheral: peripheral)
}
/* Return all available services */
private func discoverServices(peripheral: CBPeripheral) {
peripheral.discoverServices(nil)
}
private func discoverCharacteristics(peripheral: CBPeripheral) {
guard let services = peripheral.services else {
return
}
for service in services {
peripheral.discoverCharacteristics(nil, for: service)
}
}
func peripheral(_ peripheral: CBPeripheral, didDiscoverCharacteristicsFor service: CBService, error: Error?) {
guard let characteristics = service.characteristics else {
return
}
for characteristic in characteristics {
let characteristicUUID = characteristic.uuid
print("Discovered characteristic: \(characteristicUUID)")
peripheral.setNotifyValue(true, for: characteristic)
if characteristic.properties.contains(.writeWithoutResponse) {
writeCharacteristic = characteristic
print("You can write!!!") // Never read...
}
if characteristic.properties.contains(.write) {
print("You can write?")
writeCharacteristic = characteristic // Being read...
}
}
func writeToPrinter() {
guard let peripheral = connectedPeripheral else {
print("Ughhh...")
return
}
if let characteristic = writeCharacteristic {
if let data = "Hello".data(using: .utf8, allowLossyConversion: true) {
peripheral.writeValue(data, for: characteristic, type: .withoutResponse)
peripheral.writeValue(data, for: characteristic, type: .withResponse) // -> Message sent successfully
}
}
}
func peripheral(_ peripheral: CBPeripheral, didWriteValueFor characteristic: CBCharacteristic, error: Error?) {
if let error = error {
print("Writing error: \(error.localizedDescription)")
return
}
print("Message sent successfully")
}
}
My app has no trouble connecting to the bluetooth-connected printer. Initially, I called
discoverServices(peripheral:)
to get all services And I get a service identifier (5833FF01-9B8B-5191-6142-22A4536EF123) for my printer. peripheral(_:didDiscoverCharacteristicsFor:error:) doesn't return a thing for .writeWithoutResponse but does return a characteristic for .write. Eventually, if I call writeToPrinter(),
peripheral.writeValue(data, for: characteristic, type: .withoutResponse)
returns
WARNING: Characteristic <CBCharacteristic: 0x3019040c0, UUID = 5833FF02-9B8B-5191-6142-22A4536EF123, properties = 0x8, value = (null), notifying = NO> does not specify the "Write Without Response" property - ignoring response-less write
If I call
peripheral.writeValue(data, for: characteristic, type: .withResponse)
, there is no error. But I get no output from the printer. What am I doing wrong? Thanks.