我是BLE设备集成的新手。我已经实现了与BLE设备连接的代码，它已经成功连接，但现在我想传递自定义命令从该设备获取数据。
下面是需要传递给BLE设备的Json。

获取设备电量。

应用程序到设备：

{"cmd": "getBatteryLevel"}

设备到应用程序（OK响应）：

{"cmd": "getBatteryLevel", "response":100}

我试过下面。但这并不奏效。

func peripheral(_ peripheral: CBPeripheral, didDiscoverCharacteristicsFor service: CBService, error: Error?) {
    
    guard let characteristics = service.characteristics else { return }
    
    for characteristic in characteristics {
        if characteristic.properties.contains(.write) && !isValueWritten {
            // Save the characteristic for later use
            self.characteristic = characteristic
            guard let data = self.viewModel.setBLELightCommand() else { return
                print("Invalid data")
            }
            
            peripheral.writeValue(data, for: characteristic, type: .withResponse)
        }
    }
}

func convertJsonDictToData(_ dict:[String:Any])->Data?{
    do {
        let jsonData = try JSONSerialization.data(withJSONObject: dict, options: .prettyPrinted)
        // here "jsonData" is the dictionary encoded in JSON data
        guard let jsonString = String(data: jsonData, encoding: .utf8), let data = jsonString.data(using: .utf8) else {
            return nil
        }
        return data
        
    } catch {
        print(error.localizedDescription)
        return nil
    }
}

func setBLELightCommand()->Data?{
    let setLightCommand = [
        "cmd" : "setLight",
        "channel" : "0",
        "brightness" : "50",
        "state" : "ON"
    ]
    return convertJsonDictToData(setLightCommand)
}