KndKnd knd_device_ = new QModbusTcpClient; QObjectconnectknd_device_ &QModbusClientstateChangedthis &KndOnStateChanged;连接状态发生改变时处理函数connect or discennect

This code defines a constructor for the class "Knd". Inside the constructor, a new instance of the "QModbusTcpClient" class is created and assigned to the "knd_device_" member variable. Then, a connection is established between the "stateChanged" signal of the "knd_device_" object and the "OnStateChanged" slot of the "Knd" object using the "QObject::connect" function. This connection allows the "OnStateChanged" function to be called whenever the connection state of the "knd_device_" object changes (i.e. when it is connected or disconnected).