Question

I’m trying to show a busy waiting bar when one function is executing, my problem is it stop moving once the function starts.

MyProgressDialog *progBar= new MyProgressDialog();
    QProgressBar* bar = new QProgressBar(progBar);
    bar->setRange(0, 0);
    bar->setValue(0);

    progBar->setBar(bar);
    QString labeltext=QString("<qt> <center><big><b>%1</b></big></center> <br><b>%2</b><br> %3 <br><b>%4</b><br> %5</qt>")
                         .arg(progBar->labeltext)
                         .arg("File in :")
                         .arg(FileI)
                         .arg("File out :")
                         .arg(FileO);
    progBar->label->setText(labeltext);    
    progBar->setValue(10);
    progBar->show();
    progBar->setValue(20);
    Sleep(500);
    progBar->setValue(50);
    Sleep(500);
    MyFunction(FileI,FileO,mode,key);
    Sleep(500);
    progBar->setValue(80);
    Sleep(500);
    progBar->setValue(100);
    progBar->close();
    delete bar;
    delete progBar;

I warpped my function with a sleep and set value in purpose to let it moving but in vain, when I remove them MyProgressdialog didn’t show its contents, am I need to lunch my function in a separate thread ?
I tried to use QFutureWatcher:

 QFutureWatcher<void> futureWatcher;
                       QFuture<void> f1 = run(
                                              MyFunction,
                                              filePath,
                                              file.absolutePath()+"/OUT_"+fileN,
                                              1,
                                              key
                                              );
                       QObject::connect(&futureWatcher, SIGNAL(finished()), progBar, SLOT(reset()));
                       QObject::connect(progBar, SIGNAL(canceled()), &futureWatcher, SLOT(cancel()));
                       QObject::connect(&futureWatcher, SIGNAL(progressRangeChanged(int,int)), progBar, SLOT(setRange(int,int)));
                       QObject::connect(&futureWatcher, SIGNAL(progressValueChanged(int)), progBar, SLOT(setValue(int)));

                       // Start the computation.
                       futureWatcher.setFuture(f1);
                       // Display the dialog and start the event loop.
                       progBar->exec();
                       futureWatcher.waitForFinished();
                       delete progBar;

It works fine and my bar is moving when I call MyFunction just one time (for one file) but the problem occurs when I call MyFunction more than one time (for many files successively): it works but I get the same OUT_file for all files treated, I think it is multithreading issue.

EDIT: class MyProgressDialog

class MyProgressDialog: public QProgressDialog
{
  Q_OBJECT

  public:

    MyProgressDialog()
      {

      qDebug()<<"MyProgressDialog constructor";

      label=new QLabel(this);

      QPalette* palette = new QPalette();
      palette->setColor(QPalette::Window,"#F8F8FF");
      setPalette(*palette);

      QFont* font = new QFont("Courier New");
          font->setItalic(true);
          font->setPixelSize(15);
      setFont(*font);
      adjustSize();

     setWindowIcon(QIcon(QApplication::applicationDirPath()+"/icons/icon1.png"));
     setWindowFlags(Qt::WindowStaysOnTopHint);
     setMinimumWidth(500);
     setMinimumHeight(200);
     labeltext=QString("Please wait until Encryption/Decryption was done");
     label->setText(labeltext);
     label->adjustSize();
     label->setWordWrap (true);
     setLabel(label);

     setRange(0,100);
     setWindowTitle("MyFunction progress");        
     setModal(true);    

    }
    ~MyProgressDialog()
    {
        qDebug()<<"MyProgressDialog destructor";
        delete label;
    }



public:

  int value;     
  QString labeltext;
  QLabel* label;

};

Answer 1

UI in Qt is event driven. So executing your code in same thread as ui will block every ui event untill your function is finished. There are two aproaches to show progress.

1. Use thread for computing and send update events to UI
2. Easier way: after each setValue and show calls call QApplication::processEvents(); static method. Calling QApplication::processEvents() will dispatch events currently queued on event loop. Those events include all ui related events

Here is code sample for gcc/mingw gcc

#include <QApplication>
#include <QProgressBar>

int main(int argc, char * argv[])
{
    QApplication app(argc, argv);

    QProgressBar bar;
    bar.setRange(0, 100);
    bar.show();
    app.processEvents();
    usleep(250000);

    for(int i = 1; i <= 10; ++i)
    {
            bar.setValue(i * 10);
            app.processEvents();
            usleep(250000);
    }

    return 0;
}

It shows progress bar and steps it by 10 every 0,25s

Your code should look something like this:

MyProgressDialog *progBar= new MyProgressDialog();
QProgressBar* bar = new QProgressBar(progBar);
bar->setRange(0, 100); // note your "busy state won't be shown as you're changing value right after show
bar->setValue(0);

progBar->setBar(bar);
QString labeltext=QString("<qt> <center><big><b>%1</b></big></center> <br><b>%2</b><br> %3 <br><b>%4</b><br> %5</qt>")
                     .arg(progBar->labeltext)
                     .arg("File in :")
                     .arg(FileI)
                     .arg("File out :")
                     .arg(FileO);
progBar->label->setText(labeltext);    
progBar->setValue(10);
progBar->show();
QApplication::processEvents(); // HERE
progBar->setValue(20);
QApplication::processEvents(); // HERE
Sleep(500);
progBar->setValue(50);
QApplication::processEvents(); // HERE
Sleep(500);
MyFunction(FileI,FileO,mode,key);
Sleep(500);
progBar->setValue(80);
QApplication::processEvents(); // HERE
Sleep(500);
progBar->setValue(100);
progBar->close();
QApplication::processEvents(); // HERE
delete bar;
delete progBar;