蓝牙BLE中Central发送带响应写请求后无法接收Peripheral回复

已正常实现的特征读取功能 #

当前BLE特征读取功能运行正常，相关代码如下：

Central端发送读请求 #

func readCharacteristicValue() {
    if let peripheral = connectedPeripheral, let characteristic = targetCharacteristic {
        peripheral.readValue(for: characteristic)
    }
}

Peripheral端处理读请求 #

func peripheralManager(_ peripheral: CBPeripheralManager, didReceiveRead request: CBATTRequest) {
    
    // 根据服务调用不同逻辑
    switch request.characteristic.uuid {
        
    case Constants.uuid.AuthService:
            let authenticationInstance = PAuthentication.pAuthentication
            authenticationInstance.responseToReadRequest(request: request, peripheralManager: peripheralManager, clearServiceCharacteristic: clearServiceCharacteristic)
        
        case Constants.uuid.OtherService: print("Other implementation")
        
        default: print("Nothing")
    }
    
}

Central端接收读响应 #

func peripheral(_ peripheral: CBPeripheral, didUpdateValueFor characteristic: CBCharacteristic, error: Error?){
    // 处理错误
    if let error = error {
        print("Error reading characteristic value: \(error)")
    }

    // 根据响应的特征处理不同逻辑
    switch characteristic.uuid {
        
    case Constants.uuid.AuthService:
            let authenticationInstance = CAuthentication.cAuthentication
            authenticationInstance.responceFromReadRequest(characteristic: characteristic, disconnect: disconnect)
        
        default:
            print("Nothing")
    }
}

带响应写请求的问题描述 #

实现带响应的写请求时出现异常：Central端发送带响应的写请求后，Peripheral端能正常接收并处理请求，但Central端无法收到Peripheral的回复数据。

Central端写请求代码 #

func writeStringToCharacteristic(_ string: String) {
    if let data = string.data(using: .utf8), let peripheral = connectedPeripheral, let characteristic = targetCharacteristic {
        peripheral.writeValue(data, for: characteristic, type: .withResponse)
    }
}

Peripheral端处理写请求代码 #

func peripheralManager(_ peripheral: CBPeripheralManager, didReceiveWrite requests: [CBATTRequest]) {
     for request in requests {
         if request.characteristic == characteristic {
             if let value = request.value {
                 // 处理Central发送的数据示例
                 let receivedString = String(data: value, encoding: .utf8)
                 print("Received data from Central: \(receivedString ?? "")")
                 if (receivedString == "Auth"){
                     
                     var dataToSend:Data?
                     if let name = SharedData.shared.AuthData["name"],
                        let surname = SharedData.shared.AuthData["surname"],
                        let date = SharedData.shared.AuthData["date"] {
                        dataToSend = "\(name), \(surname), \(date)".data(using: .utf8)
                         // 准备通过蓝牙特征发送数据
                     } else {
                         print("One or more values are missing")
                     }
                     
                     request.value = dataToSend
                     peripheralManager.respond(to: request, withResult: .success)
                     // 无法将回复送达Central
                 }
             }
         }
     }
 }

可能的原因及排查方向 #

• 写请求响应逻辑误解：BLE协议中，带响应的写请求（.withResponse）的CBATTRequest.value字段仅用于读请求返回数据，写请求的响应仅告知Central写操作成功/失败，不会主动附带数据。若需在处理写请求后返回数据，必须使用**通知（Notify）或指示（Indicate）**机制。
• 特征属性配置不全：检查目标特征的属性，需同时开启write（或writeWithoutResponse）和notify/indicate属性，否则Peripheral无法主动推送数据给Central。
• Central端未订阅特征通知：若要接收Peripheral主动推送的数据，Central必须先调用setNotifyValue(true, for: characteristic)订阅目标特征的通知/指示。
• Central端未实现写操作回调：带响应的写请求的结果（成功/失败）需通过peripheral(_:didWriteValueFor:error:)回调接收，而非didUpdateValueFor（该回调用于接收读响应和通知数据），若未实现此回调会误以为没收到回复。

修正示例 #

Peripheral端修改：处理写请求后发送通知 #

func peripheralManager(_ peripheral: CBPeripheralManager, didReceiveWrite requests: [CBATTRequest]) {
    for request in requests {
        if request.characteristic == characteristic {
            if let value = request.value {
                let receivedString = String(data: value, encoding: .utf8)
                print("Received data from Central: \(receivedString ?? "")")
                if receivedString == "Auth" {
                    var dataToSend: Data?
                    if let name = SharedData.shared.AuthData["name"],
                       let surname = SharedData.shared.AuthData["surname"],
                       let date = SharedData.shared.AuthData["date"] {
                        dataToSend = "\(name), \(surname), \(date)".data(using: .utf8)
                    } else {
                        print("One or more values are missing")
                    }
                    
                    // 先回复写操作成功状态
                    peripheralManager.respond(to: request, withResult: .success)
                    
                    // 若有数据需要返回，通过通知发送给已订阅的Central
                    if let data = dataToSend, let targetChar = characteristic {
                        peripheralManager.updateValue(data, for: targetChar, onSubscribedCentrals: nil)
                    }
                }
            }
        }
    }
}

Central端配套修改 #

1. 订阅目标特征的通知：

// 连接Peripheral并发现特征后执行
if let peripheral = connectedPeripheral, let characteristic = targetCharacteristic {
    peripheral.setNotifyValue(true, for: characteristic)
}

2. 实现写操作结果回调：

func peripheral(_ peripheral: CBPeripheral, didWriteValueFor characteristic: CBCharacteristic, error: Error?) {
    if let error = error {
        print("Write operation failed: \(error)")
        return
    }
    print("Write operation succeeded")
}

3. 保留原didUpdateValueFor回调接收通知数据（与读响应共用）：

func peripheral(_ peripheral: CBPeripheral, didUpdateValueFor characteristic: CBCharacteristic, error: Error?){
    if let error = error {
        print("Error receiving data: \(error)")
        return
    }
    
    switch characteristic.uuid {
    case Constants.uuid.AuthService:
        let authenticationInstance = CAuthentication.cAuthentication
        authenticationInstance.responceFromReadRequest(characteristic: characteristic, disconnect: disconnect)
    default:
        print("Nothing")
    }
}

内容的提问来源于stack exchange，提问作者Emanuele Mele