Qt signals and slots for multiple objects

Question

I'm having little problem here. I'm having troubles with signals & slots. I'll try to explain with pseudocode. So, here it goes.

I have main thread (mainwindow.cpp) where I'm creating new objects when new client connects.

mainwindow.h:

signals:
   void changeText();
...

mainwindow.cpp:

connect(tcpserver, SIGNAL(changeText()), this, SIGNAL(changeText()));

...

MyClass *m = new MyClass(this);
connect(this, SIGNAL(changeText()), m, SLOT(changeText()));

I have also tcpserver class, which creates new QThread when client connects and connects both signals.

tcpserver.h:

signals:
    void changeText();
protected:
    void incomingConnection(int handle);

tcpserver.cpp:

void incomingConnection(int handle)
{
    QTcpSocket *s = new QTcpSocket(this);
    s->setSocketDescriptor(handle);
    mythread *thread = new mythread(s, this);
    connect(thread, SIGNAL(changeText()), this, SIGNAL(changeText()));
}

The problem is following: I have 3 objects, main thread, tcpserver class which inherits from QTcpServer, and the mythread class which inherits from QThread class.

When I'm creating new "mythread"-s from "tcpserver" and connecting signals, all signals from new threads are connected to "tcpserver"-s signals, so, e.g if 10 clients do something, all signals are sent to "tcpserver" which makes problem for me. I want to understand which signal should I connect to MyClass via QTread -> TcpServer -> MainWindow.

Sorry for my English, if you don't understand what I mean, I'll try to explain better.

Thank you.

I don't understand what you mean by "makes problem for me" are you trying to differentiate the incoming connections? If so you can use the int socketDescriptor as a signal argument to differentiate the calls in the MyClass slot — Viv
I'm bit confused here, because I'm new to Qt. If I pass socketDescriptor in signal, it will still cause a lot of signals to be emitted instead of one-by-one. Can you show me little example of it please? — Nika
I'm sorry but I do not understand your problem. I do not mind showing you an example provided I understand what you are trying to do. Can you update your question and state what your expected output should be and what your currently getting. — Viv
You have not stated what you want or why the current situation is a problem for you. Without either information there is no way to help. — Thomas
I'm sorry, code is really big but I can show you graph of flow how it should work. s21.postimage.org/yfm1ufudz/Signal_Slot.png If you take a look here, I want to QThread_1's signal to be connected to Object_1, QThread_2's to Object_2 and so on.. — Nika

YamHon.CHAN YamHon.CHAN · Accepted Answer · 2013-03-11T12:41:58

Some suggestions:

in your "incomingConnection(int)", i doubt any memory leak for the objects created in heap (tcpsocket, and mythread), use QList (or other container) in your tcpserver to hold the sockets created in your "incomingConnection(int)"
prefix the name of SLOT(changeText) with your classes to clarify which objects is your intented sender/receiver
I dont think you cant connect two signal like

connect(thread, SIGNAL(changeText()), this, SIGNAL(changeText()));

Qt signals and slots for multiple objects

1 Answers