qt app无法构建

Question

我正在使用Qt / C ++开发应用程序，此应用程序的目标只是定期扫描USB端口，如果应用程序找到特定的USB设备，它就会启动应用程序。

我使用过QTimer，但似乎无法正常工作。不同的搜索显示需要Q_OBJECT才能使其工作，但是一旦我添加Q_OBJECT，构建就失败了。

这是错误

Undefined symbols for architecture x86_64:
  "vtable for UsbDetection", referenced from:
      UsbDetection::UsbDetection() in usbdetection.o
      UsbDetection::~UsbDetection() in usbdetection.o
  NOTE: a missing vtable usually means the first non-inline virtual member function has no definition.

这是标题

class UsbDetection : public QObject
{
    Q_OBJECT
public:
    UsbDetection();
    ~UsbDetection();
    bool isConnected();
    QTimer *activeTimer;
    void StartAgent();

public slots:
    void ScanUSB();
};

这里是类

的c代码

UsbDetection::UsbDetection()
{
}

UsbDetection::~UsbDetection()
{
    activeTimer->deleteLater();
}

void UsbDetection::StartAgent() {
    activeTimer = new QTimer(0);
    activeTimer->setSingleShot(false);
    activeTimer->setInterval(1000);
    connect(activeTimer, SIGNAL(timeout()), this, SLOT(UsbDetection::ScanUSB()));
    activeTimer->start();

}

bool UsbDetection::isConnected() {
    libusb_context *context = NULL;
    libusb_device **list = NULL;
    bool DeviceConnected = false;
    int rc = 0;
    ssize_t count = 0;

    rc = libusb_init(&context);

    count = libusb_get_device_list(context, &list);
    if(count == 0) {
        return DeviceConnected;
    }
    for (size_t idx = 0; idx < count; ++idx) {
            libusb_device *device = list[idx];
            libusb_device_descriptor desc = {0};
            rc = libusb_get_device_descriptor(device, &desc);
            if(rc != 0) {
                return DeviceConnected;
            }
            if(desc.idVendor == PRODUCT_ID) {
                DeviceConnected = true;
                return DeviceConnected;
            }
     }
    return DeviceConnected;
}

void UsbDetection::ScanUSB() {
    if(isConnected() == true) {
        QString agentExecutableDirPath = QApplication::applicationDirPath();
        QString fileBrowserExecutablePath = agentExecutableDirPath + "/../../../../MacOS/connect";
        QProcess *process = new QProcess();
        process->startDetached(fileBrowserExecutablePath);
    }
}

我不明白为什么构建失败。