hrChar always invalid! Is somebody can help me?

[Zhang_Yubiao]

if(m_service)
{
// 服务对象创建成功后，坚挺服务状态变化，如果状态变成已发现，则进行后续服务下特征对象获取
connect(m_service,&QLowEnergyService::stateChanged, this, this
{
qDebug() << "service state change" << m_service->state() << ",||||||----";

                        //发现服务, 建立characteristic对象实例
                        if(m_service->state() == QLowEnergyService::ServiceDiscovered)
                        {
                            QLowEnergyCharacteristic hrChar = m_service->characteristic(QBluetoothUuid(QUuid("6e400003-b5a3-f393-e0a9-e50e24dcca9e")));


                            if(!hrChar.isValid())
                            {
                                qDebug() << "characteristic 6e400003-b5a3-f393-e0a9-e50e24dcca9e error:::";
                            }
                            // 设置特征对象可用
                            //enable the chracteristic notification by write 0x01 to client characteristic configuration
                            QLowEnergyDescriptor m_notificationDesc = hrChar.descriptor(QBluetoothUuid::ClientCharacteristicConfiguration);
                            if (m_notificationDesc.isValid())
                            {
                                if(hrChar.properties() & QLowEnergyCharacteristic::Notify) {
                                     qDebug() << "abcdef";
                                }
                                m_service->writeDescriptor(m_notificationDesc, QByteArray::fromHex("0100"));
                            }
                        }
                    });