一、蓝牙打印技术基础与设备适配

1.1 CoreBluetooth框架原理

iOS系统通过CoreBluetooth框架实现与蓝牙设备的通信，该框架采用GATT（Generic Attribute Profile）协议栈，支持BLE 4.0及以上设备。开发者需掌握CBPeripheralManager（服务端）和CBCentralManager（客户端）的协作机制，其中打印设备通常作为服务端提供特征值（Characteristic）供iOS端写入数据。

1.2 打印机协议解析

主流蓝牙小票打印机（如佳博、汉印）采用ESC/POS指令集，其数据传输格式包含：

• 初始化指令：\x1B\x40（重置打印机状态）
• 文字对齐：\x1B\x61\x00（左对齐）/\x01（居中）/\x02（右对齐）
• 二维码模式：\x1D\x28\x6B\x03\x00\x31\x50\x30（设置QR码模型1，版本2）
• 打印指令：\x0A（换行）/\x0C（走纸）

1.3 设备发现与连接管理

import CoreBluetooth
class BluetoothPrinterManager: NSObject, CBCentralManagerDelegate, CBPeripheralDelegate {
    private var centralManager: CBCentralManager!
    private var targetPeripheral: CBPeripheral?
    private var writeCharacteristic: CBCharacteristic?
    override init() {
        super.init()
        centralManager = CBCentralManager(delegate: self, queue: nil)
    }
    func centralManagerDidUpdateState(_ central: CBCentralManager) {
        if central.state == .poweredOn {
            central.scanForPeripherals(withServices: [CBUUID(string: "FFE0")], options: nil)
        }
    }
    func centralManager(_ central: CBCentralManager, didDiscover peripheral: CBPeripheral, advertisementData: [String : Any], rssi RSSI: NSNumber) {
        if peripheral.name?.contains("Printer") == true {
            targetPeripheral = peripheral
            central.stopScan()
            central.connect(peripheral, options: nil)
        }
    }
    func centralManager(_ central: CBCentralManager, didConnect peripheral: CBPeripheral) {
        peripheral.delegate = self
        peripheral.discoverServices([CBUUID(string: "FFE0")])
    }
    func peripheral(_ peripheral: CBPeripheral, didDiscoverServices error: Error?) {
        guard let services = peripheral.services else { return }
        for service in services {
            peripheral.discoverCharacteristics([CBUUID(string: "FFE1")], for: service)
        }
    }
    func peripheral(_ peripheral: CBPeripheral, didDiscoverCharacteristicsFor service: CBService, error: Error?) {
        guard let characteristics = service.characteristics else { return }
        for characteristic in characteristics {
            if characteristic.uuid.uuidString == "FFE1" {
                writeCharacteristic = characteristic
                print("打印机准备就绪")
            }
        }
    }
}

二、发票二维码生成与指令封装

2.1 二维码数据编码规范

根据《增值税发票税控码规范》，二维码需包含：

• 发票代码（10-12位数字）
• 发票号码（8位数字）
• 开票日期（YYYYMMDD）
• 校验码（6-20位字符）
• 金额（含税合计，单位元）

示例数据结构：

{
    "code": "123456789012",
    "number": "87654321",
    "date": "20230815",
    "checkCode": "ABC123",
    "amount": "100.50"
}

2.2 二维码指令序列构建

完整打印指令需包含：

1. 初始化序列
2. 文字信息（商户名称、交易时间等）
3. 二维码指令块
4. 切割指令（如需）
5. 走纸指令

struct PrintCommandBuilder {
    static func buildInvoiceQRCommand(invoiceData: InvoiceData) -> Data {
        var commands = Data()
        // 1. 初始化打印机
        commands.append("\x1B\x40".data(using: .ascii)!)
        // 2. 设置中文编码（如需）
        commands.append("\x1B\x74\x01".data(using: .ascii)!) // GBK编码
        // 3. 添加标题
        let title = "电子发票".centerAligned(width: 32)
        commands.append(title.data(using: .ascii)!)
        commands.append("\x0A".data(using: .ascii)!)
        // 4. 构建二维码数据
        let qrContent = """
        FPCODE:\(invoiceData.code)
        NUMBER:\(invoiceData.number)
        DATE:\(invoiceData.date)
        CHECK:\(invoiceData.checkCode)
        AMOUNT:\(invoiceData.amount)
        """
        // 5. 二维码指令（模型2，版本5，纠错L）
        let qrCommand = "\x1D\x28\x6B\x04\x00\x31\x50\x30\x05" + 
                        String(format: "%02X", qrContent.count) + 
                        qrContent + 
                        "\x1D\x28\x6B\x03\x00\x31\x51\x30"
        commands.append(qrCommand.data(using: .ascii)!)
        // 6. 走纸
        commands.append("\x0A\x0A\x0C".data(using: .ascii)!)
        return commands
    }
}
extension String {
    func centerAligned(width: Int) -> String {
        let padding = (width - count) / 2
        return String(repeating: " ", count: padding) + self
    }
}

三、完整打印流程实现

3.1 打印状态管理

class PrinterSession {
    private let manager = BluetoothPrinterManager()
    private var isPrinting = false
    func printInvoice(invoice: InvoiceData, completion: @escaping (Bool, Error?) -> Void) {
        guard !isPrinting else {
            completion(false, PrinterError.busy)
            return
        }
        isPrinting = true
        let command = PrintCommandBuilder.buildInvoiceQRCommand(invoiceData: invoice)
        DispatchQueue.global().async {
            let semaphore = DispatchSemaphore(value: 0)
            self.manager.writeData(command) { success, error in
                self.isPrinting = false
                completion(success, error)
                semaphore.signal()
            }
            semaphore.wait()
        }
    }
}
extension BluetoothPrinterManager {
    func writeData(_ data: Data, completion: @escaping (Bool, Error?) -> Void) {
        guard let characteristic = writeCharacteristic else {
            completion(false, PrinterError.notConnected)
            return
        }
        targetPeripheral?.writeValue(data, for: characteristic, type: .withResponse) { error in
            if let error = error {
                completion(false, error)
            } else {
                completion(true, nil)
            }
        }
    }
}

3.2 异常处理机制

需重点处理的异常场景：

1. 连接超时：设置10秒超时重试机制
2. 指令格式错误：验证打印机支持的二维码版本
3. 数据截断：检查特征值MTU（通常20字节）
4. 打印卡纸：监听打印机状态特征值

enum PrinterError: Error {
    case notConnected
    case busy
    case timeout
    case invalidData
    case unknown(Error)
}
class RetryPolicy {
    static func withRetry<T>(maxAttempts: Int = 3, 
                             delay: TimeInterval = 2,
                             operation: @escaping () -> (T?, Error?)) -> (T?, Error?) {
        var lastError: Error?
        for attempt in 1...maxAttempts {
            let result = operation()
            if let value = result.0 {
                return (value, nil)
            } else if let error = result.1 {
                lastError = error
                if attempt < maxAttempts {
                    Thread.sleep(forTimeInterval: delay)
                }
            }
        }
        return (nil, lastError ?? PrinterError.unknown(NSError(domain: "", code: 0, userInfo: nil)))
    }
}

四、性能优化与兼容性处理

4.1 指令分包传输

当打印数据超过特征值MTU时，需实现分包逻辑：

extension Data {
    func chunked(for characteristic: CBCharacteristic) -> [Data] {
        let mtu = characteristic.maximumWriteValueLength - 3 // 减去ATT头开销
        var chunks = [Data]()
        var offset = 0
        while offset < count {
            let endIndex = min(offset + mtu, count)
            let chunk = subdata(in: offset..<endIndex)
            chunks.append(chunk)
            offset = endIndex
        }
        return chunks
    }
}

4.2 打印机型号适配

不同厂商指令差异处理：

protocol PrinterProtocol {
    func initialize() -> Data
    func setQRModel(version: Int, errorCorrection: Int) -> Data
    func printQR(data: String) -> Data
}
class GenericPrinter: PrinterProtocol {
    func initialize() -> Data { "\x1B\x40".data(using: .ascii)! }
    // ...其他默认实现
}
class HanxinPrinter: GenericPrinter {
    override func setQRModel(version: Int, errorCorrection: Int) -> Data {
        // 汉印特殊指令格式
        return "\x1D\x28\x6B\x03\x00\x31\x52\x30".data(using: .ascii)!
    }
}

五、实际应用建议

1. 打印预览：在发送指令前，使用Core Graphics生成预览图
2. 日志记录：保存每次打印的指令和结果，便于故障排查
3. 固件更新：检查打印机是否支持动态二维码版本调整
4. 能耗优化：在非打印时段断开蓝牙连接

通过上述技术实现，开发者可以构建稳定可靠的iOS蓝牙打印系统，满足电子发票二维码的合规打印需求。实际开发中需结合具体打印机型号的文档进行指令微调，并通过大量测试验证兼容性。