[Solved] Easy way to run loops without GUI freezing?

Zamahra

Hello there,

I've got a little problem which i can't solve by myself. I have written a program which recieves pictures from a TCP-Socket. The program has to start and find its server by itself, because the computer it's going to run on hasn't got a monitor or a keyboard. When the program starts, it checks an IP-List for a running server. Following function is called from the GUI:

@void MultiClientSocket::firstTryConnect()
{
QString helper = QString::number(host);

blockSignals(true);                                                                                                                            
int counter = 0;
while((state() == QAbstractSocket::UnconnectedState) == true)                                                             
{
    ipAddress = ipList.at(counter);
    connectToHost(ipAddress,host,QIODevice::ReadWrite);
    if(waitForConnected(200))
        break;

    if((counter == (ipList.size()-1))==true)
    {
        counter = 0;
    }
    else
    {
        counter++;
    }
}
disconnectFromHost();                                                                                                      
blockSignals(false);
emit setIP(ipAddress);
QTimer::singleShot(100,this,SLOT(tryConnect()));                                                                         
emit setStatus("Connecting...");

}@

Of course the GUI is freezing when the program is searching for a server. I know there are many ways to stop that, with threading for example. But I don't know how to use them. Is there a possibility without threading or finding a running server without connecting?

Thank you for your help!

Zamahra

I'm using QT 5.0.1 with QT Creator 2.6.2 on a Windows 7 64Bit Computer

sierdzio

You can use qApp::processEvents() inside your loop to keep the GUI responsive. It's probably better to rethink the design, though.

raven-worx

why do you care if the gui freezes when the program is supposted to run on a computer without keyboard and a monitor? :)

SetBetterPass

You can try "QEventLoop":http://qt-project.org/doc/qt-5.0/qtcore/qeventloop.html

MuldeR

You probably want to put functions that take a lot of time into a "background" thread.

You can emit a signal from the "background" thread and then have the GUI thread react on it in a slot, as soon as the final result is known or some status update (which the GUI needs to know about) has occurred.

Use the Qt::QueuedConnection connection type for this purpose, so the slot will be executed in "main" thread.

--

See also:

Zamahra

Thank you for your help!

@qApp->processEvents();@
works very fine.

Even when the program should start by itself, I have to use the GUI for test-purposes. I think its better when the program runs on every computer and doesn't confuse users by freezing =)

MuldeR

Nevertheless, keep in mind that qApp->processEvents() processes all pending events, which means that it may process also pending signals, which in turn, may call into slot functions - which probably is not what you want in the middle of your loop. Also, it can easily construct a nice infinite recursion, if you call qApp->processEvents() from within a slot, as it might result in calling exactly that slot. So, you have to be very careful with it...

(Doesn't mean it can't work nice for your particular program)