Update GUI from another thread

Hi Everyone!

I'm struggling with the following problem for quite some time. My application runs heavy mathematical equations based on input files. The actual work is done within a separate thread. This way the GUI remains responsive. Everything works great, but I just can't figure out how to update the GUI from the separate thread. While processing the equations I want the GUI to show which equation is currently processed.

I just recently started using QT. This because I need to develop a application that runs on both Windows and Mac. The concept of slots is hard to me. I have developed many applications using Xcode and Cocoa. In this environment I can create complicated multithreading applications (that continuously update the GUI) without any problem. My C++ knowledge is average.

It drives me crazy. I spend to much time figuring this out. And still no result.

To the point:
Who can create an sample project for me?

The sample must contain:
- GUI with one text-box / button
- Clicking the button starts a new thread
- The new thread executes a loop 5 times.
- The loop simulates a heavy process (for example by using 1-second sleep)
- Every time the loop starts the GUI is updated by appending a line to the textbox.

I'm willing to pay for your time. I definitely need some help here. Please keep the sample as simple as possible. This way i can understand how it works.

(A little desperate)
Kind regards,
Anne

How does your thread look like? Add in *.h file

Code:

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Q_SIGNALS:
void currentEquitation(QString);

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In the cpp, where you calculate a new equation simple do

Code:

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Q_EMIT currentEquitation("Equitation foo");

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And then in your GUI class where you start your thread (assuming it is called thread and you have a QLabel called label):

Code:

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QObject::connect(thread, SIGNAL(currentEquitation(QString)), label, SLOT(setText(QString)));

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That's all.

Hi,

Hope this simple example will help you.

You don't have to subclass QThread, you can simply use existing classes for compilation and use them "directly":

Code:

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#include <QtGui>
 
 
class calc : public QObject
{
    Q_OBJECT
 
  public Q_SLOTS:
    void doCalc()
    {
      for (int i = 1; i < 25; ++i)
      {
        Q_EMIT message(QString::number(i));
        QTime t = QTime::currentTime();
        t = t.addSecs(2);
        while (t > QTime::currentTime()) {}
      }
    }
 
  Q_SIGNALS:
    void message(QString);
};
 
 
int main(int argv, char** args)
{
  QApplication app(argv, args);
 
  // GUI
  QWidget w;
  QPushButton* b = new QPushButton("start", &w);
  QLabel* l = new QLabel(&w);
  QLineEdit* le = new QLineEdit(&w);
  QVBoxLayout* la = new QVBoxLayout();
  la->addWidget(l);
  la->addWidget(b);
  la->addWidget(le);
  w.setLayout(la);
  w.show();
 
  // Thread
  calc c;
  QThread t;
  c.moveToThread(&t);
  t.start();
 
  // Connections
  QObject::connect(&c, SIGNAL(message(QString)), l, SLOT(setText(QString)));
  QObject::connect(b, SIGNAL(clicked()), &c, SLOT(doCalc()));
 
  return app.exec();
}
 
#include "main.moc"

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Quote:

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Originally Posted by Anne

I'm willing to pay for your time.

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If you want to offer a job, even if it is a small one, please use your "Jobs" forum.

Nevertheless, if you found the answers usefull, nobody will stop you if you spend some money to QtCentre.org or KDE e.V. or or or... :)

Dear Lykurg and ^NyAw^,

Wow, is it just that simple?! QT really amazes me.

You really helped me out here, everything is perfectly clear right now. I was thinking too complicated. In Xcode / Cocoa it's actually much harder to do exactly this. If you ever have any Xcode / Cocoa related question, please contact me!

Generally I never ask for help. I want to figure out things like these myself. In the long run this is the best way to learn a new language in my opinion. But in this case I was completely stuck.

I did not really intend to offer a job, was just asking for an example. Please give me some info on how to donate to qtcentre.org (can't find the PayPal address). I love communities like these and always support them.

All your help is greatly appreciated,
Kind regards,
Anne

Quote:

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Originally Posted by Anne

Please give me some info on how to donate to qtcentre.org (can't find the PayPal address). I love communities like these and always support them.

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Qt Centre paypal account is foundation at qtcentre.org.

@wysota
Thanks for the address!

@^NyAw^ and Others
I tried to open your sample project, but the folder does not contain any .pro files.
The only files I see are .h, .cpp, .ui and .qrc.
How can I open such an project directly with QT? The .qrc is not recognized?
(Of cours I now just directly used the .cpp and .h files, but was just curious)

You can run "qmake -project" inside that folder. Then Qt is generating a pro file for you.

Hi,

Quote:

---

Originally Posted by Anne

@^NyAw^ and Others
I tried to open your sample project, but the folder does not contain any .pro files.
The only files I see are .h, .cpp, .ui and .qrc.
How can I open such an project directly with QT? The .qrc is not recognized?
(Of cours I now just directly used the .cpp and .h files, but was just curious)

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I just don't added the pro file because I'm using Visual Studio on Windows and I'm not using the pro file, but there is an option to create the pro file that then I can attach.
Just use "qmake -project" as Lykurg said to create the "pro" file and then call "make" to compile the project.

Quote:

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Originally Posted by Anne

Generally I never ask for help

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It's a good idea to learn by yourself, but sometimes the examples don't show what you are expecting or you are not able really how something works. Then, ask the forum! (but first of all try to find similar posts on it).