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Function after setupUi()

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  • T t0msk
    5 Feb 2017, 13:13

    @kshegunov said in Function after setupUi():

    You can't because you're assuming you can know when the last paint event is going to be dispatched and which paint event is "last", which is equivalent to asking a psychic about the future. We are talking event-driven programming here, so just respond to the relevant events. What is it that you want to do in that function anyway?

    In function will be connecting to server, getting data from server, parsing data, etc. So I would like to create Dialog with progressbar like loader, which shows you what is program currently doing.

    It is simple loader window, lot of apps use this.

    I am looking for Form_Load function like in C#

    M Offline
    M Offline
    mrjj
    Lifetime Qt Champion
    wrote on 5 Feb 2017, 16:17 last edited by mrjj 2 May 2017, 16:17
    #7

    @t0msk
    To be sure main window is fully shown and then app will popup a Dialog over it then you can use

    void MainWindow::showEvent( QShowEvent* event ) {
        QMainWindow::showEvent( event );
        //your code here
    
    } 
    
    T 1 Reply Last reply 5 Feb 2017, 16:54
    0
    • M mrjj
      5 Feb 2017, 16:17

      @t0msk
      To be sure main window is fully shown and then app will popup a Dialog over it then you can use

      void MainWindow::showEvent( QShowEvent* event ) {
          QMainWindow::showEvent( event );
          //your code here
      
      } 
      
      T Offline
      T Offline
      t0msk
      wrote on 5 Feb 2017, 16:54 last edited by
      #8

      @mrjj

      It doesnt work

      I added into mainwindow.cpp:

      void MainWindow::showEvent( QShowEvent* event ) {
          QMainWindow::showEvent( event );
          //your code here
      
          QThread::sleep(10);
      
          ui->progressBar->setValue(80);
      }
      

      and mainwindow.h:

      public:
          explicit MainWindow(QWidget *parent = 0);
          ~MainWindow();
          void showEvent(QShowEvent* event);
      

      Problem is that, mainwindow shows after 10 seconds.

      Student who loves C/C++

      M 1 Reply Last reply 5 Feb 2017, 16:56
      0
      • T t0msk
        5 Feb 2017, 16:54

        @mrjj

        It doesnt work

        I added into mainwindow.cpp:

        void MainWindow::showEvent( QShowEvent* event ) {
            QMainWindow::showEvent( event );
            //your code here
        
            QThread::sleep(10);
        
            ui->progressBar->setValue(80);
        }
        

        and mainwindow.h:

        public:
            explicit MainWindow(QWidget *parent = 0);
            ~MainWindow();
            void showEvent(QShowEvent* event);
        

        Problem is that, mainwindow shows after 10 seconds.

        M Offline
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        mrjj
        Lifetime Qt Champion
        wrote on 5 Feb 2017, 16:56 last edited by
        #9

        @t0msk

        Hi
        Do not use QThread::sleep(10);
        You Freeze whole appfor 10 secs... :)

        T 1 Reply Last reply 5 Feb 2017, 17:05
        2
        • T t0msk
          5 Feb 2017, 13:13

          @kshegunov said in Function after setupUi():

          You can't because you're assuming you can know when the last paint event is going to be dispatched and which paint event is "last", which is equivalent to asking a psychic about the future. We are talking event-driven programming here, so just respond to the relevant events. What is it that you want to do in that function anyway?

          In function will be connecting to server, getting data from server, parsing data, etc. So I would like to create Dialog with progressbar like loader, which shows you what is program currently doing.

          It is simple loader window, lot of apps use this.

          I am looking for Form_Load function like in C#

          K Offline
          K Offline
          kshegunov
          Moderators
          wrote on 5 Feb 2017, 16:57 last edited by kshegunov 2 May 2017, 16:58
          #10

          @t0msk said in Function after setupUi():

          I am looking for Form_Load function like in C#

          I don't know C#, but from a quick search it appears you want to put that code in the constructor after the setupUi call. Nothing is shown until the events are processed, so I don't see why you want to know when the window's shown. Just create your dialog and call show() on it (don't call exec() as it will block the event loop). Connect the signals and slots as appropriate for the case. The data fetching and/or processing you can offload to a worker thread (for example take a look at the concurrent framework).

          @mrjj said in Function after setupUi():

          To be sure main window is fully shown and then app will popup a Dialog over it then you can use

          True, however you are probably going to get multiple show events, so then that part of the code would be executed multiple times. Additionally, you may not have a correct geometry at the time as there's no specific documented order of events; it all will depend on the underlying window manager (although from my experience one gets the show event last at least for Win and X11).

          Read and abide by the Qt Code of Conduct

          1 Reply Last reply
          1
          • M mrjj
            5 Feb 2017, 16:56

            @t0msk

            Hi
            Do not use QThread::sleep(10);
            You Freeze whole appfor 10 secs... :)

            T Offline
            T Offline
            t0msk
            wrote on 5 Feb 2017, 17:05 last edited by
            #11

            @mrjj said in Function after setupUi():

            @t0msk

            Hi
            Do not use QThread::sleep(10);
            You Freeze whole appfor 10 secs... :)

            Is there something else that sleep? Is there for example wait? Because sleep can means that app will freeze, but thread is locked in your app, something like mutex if you want to free thread.

            @kshegunov

            My goal is that app will show Dialog where is progress bar and after all data fetching/processing is shown mainwindow and dialog closed.

            Student who loves C/C++

            K 1 Reply Last reply 5 Feb 2017, 17:12
            0
            • T t0msk
              5 Feb 2017, 17:05

              @mrjj said in Function after setupUi():

              @t0msk

              Hi
              Do not use QThread::sleep(10);
              You Freeze whole appfor 10 secs... :)

              Is there something else that sleep? Is there for example wait? Because sleep can means that app will freeze, but thread is locked in your app, something like mutex if you want to free thread.

              @kshegunov

              My goal is that app will show Dialog where is progress bar and after all data fetching/processing is shown mainwindow and dialog closed.

              K Offline
              K Offline
              kshegunov
              Moderators
              wrote on 5 Feb 2017, 17:12 last edited by
              #12

              @t0msk said in Function after setupUi():

              Is there something else that sleep?

              The point is you should not sleep.

              My goal is that app will show Dialog where is progress bar and after all data fetching/processing is shown mainwindow and dialog closed.

              Fine, so why have a main window at all. Also this in no way contradicts what I wrote, just call show() on whatever widget you want to show and connect the signals and slots appropriately.

              Read and abide by the Qt Code of Conduct

              1 Reply Last reply
              1
              • T Offline
                T Offline
                t0msk
                wrote on 5 Feb 2017, 18:34 last edited by t0msk 2 May 2017, 18:35
                #13

                ok, so I created quite hard function for CPU, without sleep:

                void MainWindow::showEvent( QShowEvent* event ) {
                    QMainWindow::showEvent( event );
                    //your code here
                
                    ui->progressBar->setValue(20);
                
                    int i;
                    double result;
                    QString string;
                
                    for(i = 0;i < 5000000;i++) {
                
                        result = ((((i * 1337) / 7) * 3) - 5) % 1937;
                
                        string = QString::number(result);
                
                        ui->label->setText(string);
                    }
                
                    ui->progressBar->setValue(80);
                }
                

                It took some seconds, BUT window displayed after math, so I cannot see initial value of progress bar (20). Sorry but I am confused.

                Student who loves C/C++

                K 1 Reply Last reply 5 Feb 2017, 20:25
                1
                • T t0msk
                  5 Feb 2017, 18:34

                  ok, so I created quite hard function for CPU, without sleep:

                  void MainWindow::showEvent( QShowEvent* event ) {
                      QMainWindow::showEvent( event );
                      //your code here
                  
                      ui->progressBar->setValue(20);
                  
                      int i;
                      double result;
                      QString string;
                  
                      for(i = 0;i < 5000000;i++) {
                  
                          result = ((((i * 1337) / 7) * 3) - 5) % 1937;
                  
                          string = QString::number(result);
                  
                          ui->label->setText(string);
                      }
                  
                      ui->progressBar->setValue(80);
                  }
                  

                  It took some seconds, BUT window displayed after math, so I cannot see initial value of progress bar (20). Sorry but I am confused.

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                  kshegunov
                  Moderators
                  wrote on 5 Feb 2017, 20:25 last edited by
                  #14

                  Here, however I provide no text here as instruction. You need to read what an event loop is, how it relates to the GUI, what blocking the event loop means and how one can process things without blocking the event loop (multiple topics all available in the documentation).

                  #include <QApplication>
                  #include <QProgressDialog>
                  #include <QTimer>
                  
                  int main(int argc, char ** argv)
                  {
                      QApplication application(argc, argv);
                  
                      QTimer timer;
                      timer.setInterval(100); //< Simulates a long running operation in the background
                      timer.start();
                  
                      QProgressDialog dialog(QStringLiteral("Test dialog"), QStringLiteral("Cancel"), 0, 100);
                      dialog.show();
                  
                      int counter = 0;
                      QObject::connect(&timer, &QTimer::timeout, &dialog, [&dialog, &timer, &counter] () -> void {
                          counter++;
                          if (counter >= dialog.maximum())  {
                              timer.stop();
                              dialog.close();
                              return;
                          }
                  
                          dialog.setValue(counter);
                      });
                  
                      QObject::connect(&dialog, &QProgressDialog::canceled, &timer, &QTimer::stop);
                      QObject::connect(&dialog, &QProgressDialog::canceled, &application, &QApplication::quit);
                  
                      return QApplication::exec();
                  }
                  

                  Read and abide by the Qt Code of Conduct

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                    J.Hilk
                    Moderators
                    wrote on 6 Feb 2017, 05:50 last edited by
                    #15

                    Hi,

                    I would suggest looking into QSplashScreen it might me the class for your problems.

                    If I understand it correctly, you want to paint the gui, and than initialize the rest of your program displayed by a progressbar.

                    Simplest way to do this would be to call

                    QTimer::singleShot(10,this,&YourClass::SetupWithProgressbar);
                    

                    out of your constructor, right after

                    ui->setupUi(this);
                    

                    but, if your SetupCode is in the same thread as your progressbar, the pbar will most likely not update itself correctly. You'll have to do that manualy.

                    I hope this helps.


                    Be aware of the Qt Code of Conduct, when posting : https://forum.qt.io/topic/113070/qt-code-of-conduct


                    Q: What's that?
                    A: It's blue light.
                    Q: What does it do?
                    A: It turns blue.

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                      t0msk
                      wrote on 6 Feb 2017, 14:11 last edited by
                      #16

                      @J.Hilk said in Function after setupUi():

                      If I understand it correctly, you want to paint the gui, and than initialize the rest of your program displayed by a progressbar.

                      Exactly!

                      So my code now looks like this:

                      #include "mainwindow.h"
                      #include "ui_mainwindow.h"
                      
                      #include "QTimer"
                      #include "QThread"
                      
                      void MainWindow::SetupWithProgressbar() {
                      
                          ui->progressBar->setValue(20);
                      
                          int i;
                          double result;
                          QString string;
                      
                          for(i = 0;i < 5000000;i++) {
                      
                              result = ((((i * 1337) / 7) * 3) - 5) % 1937;
                      
                              string = QString::number(result);
                      
                              ui->label->setText(string);
                          }
                      
                          ui->progressBar->setValue(80);
                      }
                      
                      MainWindow::MainWindow(QWidget *parent) :
                          QMainWindow(parent),
                          ui(new Ui::MainWindow)
                      {
                          ui->setupUi(this);
                      
                          QTimer::singleShot(10, this, MainWindow::SetupWithProgressbar());
                      }
                      
                      MainWindow::~MainWindow()
                      {
                          delete ui;
                      }
                      

                      But I am getting an error:

                      error: invalid use of void expression
                           QTimer::singleShot(10, this, MainWindow::SetupWithProgressbar());
                                                                              ^
                      

                      I think it is correct.

                      @kshegunov said in Function after setupUi():

                      Here, however I provide no text here as instruction. You need to read what an event loop is, how it relates to the GUI, what blocking the event loop means and how one can process things without blocking the event loop (multiple topics all available in the documentation).

                      #include <QApplication>
                      #include <QProgressDialog>
                      #include <QTimer>
                      
                      int main(int argc, char ** argv)
                      {
                          QApplication application(argc, argv);
                      
                          QTimer timer;
                          timer.setInterval(100); //< Simulates a long running operation in the background
                          timer.start();
                      
                          QProgressDialog dialog(QStringLiteral("Test dialog"), QStringLiteral("Cancel"), 0, 100);
                          dialog.show();
                      
                          int counter = 0;
                          QObject::connect(&timer, &QTimer::timeout, &dialog, [&dialog, &timer, &counter] () -> void {
                              counter++;
                              if (counter >= dialog.maximum())  {
                                  timer.stop();
                                  dialog.close();
                                  return;
                              }
                      
                              dialog.setValue(counter);
                          });
                      
                          QObject::connect(&dialog, &QProgressDialog::canceled, &timer, &QTimer::stop);
                          QObject::connect(&dialog, &QProgressDialog::canceled, &application, &QApplication::quit);
                      
                          return QApplication::exec();
                      }
                      

                      Isnt it quite complicated for such simple thing? :/

                      Student who loves C/C++

                      J K 2 Replies Last reply 6 Feb 2017, 14:16
                      0
                      • T t0msk
                        6 Feb 2017, 14:11

                        @J.Hilk said in Function after setupUi():

                        If I understand it correctly, you want to paint the gui, and than initialize the rest of your program displayed by a progressbar.

                        Exactly!

                        So my code now looks like this:

                        #include "mainwindow.h"
                        #include "ui_mainwindow.h"
                        
                        #include "QTimer"
                        #include "QThread"
                        
                        void MainWindow::SetupWithProgressbar() {
                        
                            ui->progressBar->setValue(20);
                        
                            int i;
                            double result;
                            QString string;
                        
                            for(i = 0;i < 5000000;i++) {
                        
                                result = ((((i * 1337) / 7) * 3) - 5) % 1937;
                        
                                string = QString::number(result);
                        
                                ui->label->setText(string);
                            }
                        
                            ui->progressBar->setValue(80);
                        }
                        
                        MainWindow::MainWindow(QWidget *parent) :
                            QMainWindow(parent),
                            ui(new Ui::MainWindow)
                        {
                            ui->setupUi(this);
                        
                            QTimer::singleShot(10, this, MainWindow::SetupWithProgressbar());
                        }
                        
                        MainWindow::~MainWindow()
                        {
                            delete ui;
                        }
                        

                        But I am getting an error:

                        error: invalid use of void expression
                             QTimer::singleShot(10, this, MainWindow::SetupWithProgressbar());
                                                                                ^
                        

                        I think it is correct.

                        @kshegunov said in Function after setupUi():

                        Here, however I provide no text here as instruction. You need to read what an event loop is, how it relates to the GUI, what blocking the event loop means and how one can process things without blocking the event loop (multiple topics all available in the documentation).

                        #include <QApplication>
                        #include <QProgressDialog>
                        #include <QTimer>
                        
                        int main(int argc, char ** argv)
                        {
                            QApplication application(argc, argv);
                        
                            QTimer timer;
                            timer.setInterval(100); //< Simulates a long running operation in the background
                            timer.start();
                        
                            QProgressDialog dialog(QStringLiteral("Test dialog"), QStringLiteral("Cancel"), 0, 100);
                            dialog.show();
                        
                            int counter = 0;
                            QObject::connect(&timer, &QTimer::timeout, &dialog, [&dialog, &timer, &counter] () -> void {
                                counter++;
                                if (counter >= dialog.maximum())  {
                                    timer.stop();
                                    dialog.close();
                                    return;
                                }
                        
                                dialog.setValue(counter);
                            });
                        
                            QObject::connect(&dialog, &QProgressDialog::canceled, &timer, &QTimer::stop);
                            QObject::connect(&dialog, &QProgressDialog::canceled, &application, &QApplication::quit);
                        
                            return QApplication::exec();
                        }
                        

                        Isnt it quite complicated for such simple thing? :/

                        J Offline
                        J Offline
                        J.Hilk
                        Moderators
                        wrote on 6 Feb 2017, 14:16 last edited by
                        #17

                        @t0msk said in Function after setupUi():

                        error: invalid use of void expression
                             QTimer::singleShot(10, this, MainWindow::SetupWithProgressbar());
                                                                                ^
                        

                        You're using the wrong syntax,

                        Use ne new one

                        QTimer::singleShot(10, this, &MainWindow::SetupWithProgressbar);
                        

                        or the old one

                        QTimer::singleShot(10, this, SLOT(SetupWithProgressbar()));
                        

                        If you mix them, the compiler will complain :)


                        Be aware of the Qt Code of Conduct, when posting : https://forum.qt.io/topic/113070/qt-code-of-conduct


                        Q: What's that?
                        A: It's blue light.
                        Q: What does it do?
                        A: It turns blue.

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                          t0msk
                          wrote on 6 Feb 2017, 14:29 last edited by
                          #18

                          @J.Hilk said in Function after setupUi():

                          @t0msk said in Function after setupUi():

                          error: invalid use of void expression
                               QTimer::singleShot(10, this, MainWindow::SetupWithProgressbar());
                                                                                  ^
                          

                          You're using the wrong syntax,

                          Use ne new one

                          QTimer::singleShot(10, this, &MainWindow::SetupWithProgressbar);
                          

                          or the old one

                          QTimer::singleShot(10, this, SLOT(SetupWithProgressbar()));
                          

                          If you mix them, the compiler will complain :)

                          Ah yes there is newer syntax :D So app was compiled successfully, but window displayed without UI (app freezes until math was completed), so i didint see "changing" progress bar.

                          Student who loves C/C++

                          M 1 Reply Last reply 6 Feb 2017, 14:35
                          0
                          • T t0msk
                            6 Feb 2017, 14:29

                            @J.Hilk said in Function after setupUi():

                            @t0msk said in Function after setupUi():

                            error: invalid use of void expression
                                 QTimer::singleShot(10, this, MainWindow::SetupWithProgressbar());
                                                                                    ^
                            

                            You're using the wrong syntax,

                            Use ne new one

                            QTimer::singleShot(10, this, &MainWindow::SetupWithProgressbar);
                            

                            or the old one

                            QTimer::singleShot(10, this, SLOT(SetupWithProgressbar()));
                            

                            If you mix them, the compiler will complain :)

                            Ah yes there is newer syntax :D So app was compiled successfully, but window displayed without UI (app freezes until math was completed), so i didint see "changing" progress bar.

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                            mrjj
                            Lifetime Qt Champion
                            wrote on 6 Feb 2017, 14:35 last edited by mrjj 2 Jun 2017, 14:37
                            #19

                            @t0msk
                            well as long as you keep block the app , it will freeze like that

                            When you do
                            for(i = 0;i < 5000000;i++) {

                            You kill the event loop and hence nothing else work.

                            An ugly and not recommended way is to call
                            QCoreApplication::processEvents()
                            in such loops but its not good design and not needed if you stop blocking it with loops.

                            T 1 Reply Last reply 6 Feb 2017, 14:40
                            0
                            • M mrjj
                              6 Feb 2017, 14:35

                              @t0msk
                              well as long as you keep block the app , it will freeze like that

                              When you do
                              for(i = 0;i < 5000000;i++) {

                              You kill the event loop and hence nothing else work.

                              An ugly and not recommended way is to call
                              QCoreApplication::processEvents()
                              in such loops but its not good design and not needed if you stop blocking it with loops.

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                              t0msk
                              wrote on 6 Feb 2017, 14:40 last edited by t0msk 2 Jun 2017, 14:42
                              #20

                              @mrjj said in Function after setupUi():

                              @t0msk
                              well as long as you keep block the app , it will freeze like that

                              When you do
                              for(i = 0;i < 5000000;i++) {

                              You kill the event loop and hence nothing else work.

                              An ugly and not recommended way is to call
                              QCoreApplication::processEvents()
                              in such loops but its not good design and not needed if you stop blocking it with loops.

                              I know that I am blocking app, but I dont know how can I create some "logic" (because every logic will occupy CPU) and display it by a progressbar.

                              Student who loves C/C++

                              M 1 Reply Last reply 6 Feb 2017, 14:43
                              0
                              • T t0msk
                                6 Feb 2017, 14:40

                                @mrjj said in Function after setupUi():

                                @t0msk
                                well as long as you keep block the app , it will freeze like that

                                When you do
                                for(i = 0;i < 5000000;i++) {

                                You kill the event loop and hence nothing else work.

                                An ugly and not recommended way is to call
                                QCoreApplication::processEvents()
                                in such loops but its not good design and not needed if you stop blocking it with loops.

                                I know that I am blocking app, but I dont know how can I create some "logic" (because every logic will occupy CPU) and display it by a progressbar.

                                M Offline
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                                mrjj
                                Lifetime Qt Champion
                                wrote on 6 Feb 2017, 14:43 last edited by
                                #21

                                @t0msk

                                Ok. so u know that the LOOP is the reason it do not work and you see NO change in the progress bar ?

                                Anyway, what is wrong with @kshegunov code ?
                                its 100% non blocking.

                                1 Reply Last reply
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                                  t0msk
                                  wrote on 6 Feb 2017, 16:11 last edited by
                                  #22

                                  @mrjj said in Function after setupUi():

                                  @t0msk

                                  Ok. so u know that the LOOP is the reason it do not work and you see NO change in the progress bar ?

                                  Anyway, what is wrong with @kshegunov code ?
                                  its 100% non blocking.

                                  Because I dont understand it, why there is timer? why is he setting a value into dialog and what is it mean?, I am newbie in Qt, so I am looking for simpler solution.

                                  I used this in C# and it worked out of box.

                                  Student who loves C/C++

                                  M 1 Reply Last reply 6 Feb 2017, 17:09
                                  0
                                  • T t0msk
                                    6 Feb 2017, 16:11

                                    @mrjj said in Function after setupUi():

                                    @t0msk

                                    Ok. so u know that the LOOP is the reason it do not work and you see NO change in the progress bar ?

                                    Anyway, what is wrong with @kshegunov code ?
                                    its 100% non blocking.

                                    Because I dont understand it, why there is timer? why is he setting a value into dialog and what is it mean?, I am newbie in Qt, so I am looking for simpler solution.

                                    I used this in C# and it worked out of box.

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                                    mrjj
                                    Lifetime Qt Champion
                                    wrote on 6 Feb 2017, 17:09 last edited by mrjj 2 Jun 2017, 17:09
                                    #23

                                    @t0msk
                                    His example just makes the dialog have a counter (progress) as to simulate something is going on. like
                                    downloading a patch.
                                    The timer will post a "timeout" to the event loop ( which in this case is NOT blocked) and
                                    the dialog can update and "do stuff"

                                    The syntax
                                    "QObject::connect(&timer, &QTimer::timeout, &dialog, [&dialog, &timer, &counter] () ->"
                                    just creates a function in the spot. So all inside
                                    {
                                    // normal slot code.
                                    }
                                    Is just the code you would put in a normal slot function.
                                    This allows for the logic to be in main and not inside mainwindow.

                                    So the timer allows to draw and update the Progress while for loops do not as easy.

                                    Hope this makes it more clear.

                                    T 1 Reply Last reply 7 Feb 2017, 11:34
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                                      J.Hilk
                                      Moderators
                                      wrote on 7 Feb 2017, 05:44 last edited by J.Hilk 2 Jul 2017, 06:46
                                      #24

                                      I personaly would approach this situation differently from what was suggestet so far.

                                      The "proper" way would be to put your "CPU-heavy function" in a different thread and use Signal/Slots to update the UI.

                                      something along the lines:

                                      *.h:

                                      signals:
                                          void pBarSetValue(int value);
                                          void showResult(QString result);
                                      

                                      *.cpp

                                      ui->setupUi(this);
                                      
                                      connect(this, &MyClass::pBarSetValue, ui->progressBar, QProgressBar::setValue);
                                      connect(this, &MyClass::showResult, ui->label, &QLabel::setText);
                                      
                                      ui->progressBar->setRange(0,5000000);
                                      
                                      
                                      QtConcurrent::run([=]() {
                                          for(i = 0;i < 5000000;i++) {
                                      
                                                double dResult = ((((i * 1337) / 7) * 3) - 5) % 1937;
                                      
                                                emit showResult(QString::number(dResult));
                                                emit pBarSetValue(i);
                                          }
                                      }
                                      

                                      Be aware of the Qt Code of Conduct, when posting : https://forum.qt.io/topic/113070/qt-code-of-conduct


                                      Q: What's that?
                                      A: It's blue light.
                                      Q: What does it do?
                                      A: It turns blue.

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                                      2
                                      • T t0msk
                                        6 Feb 2017, 14:11

                                        @J.Hilk said in Function after setupUi():

                                        If I understand it correctly, you want to paint the gui, and than initialize the rest of your program displayed by a progressbar.

                                        Exactly!

                                        So my code now looks like this:

                                        #include "mainwindow.h"
                                        #include "ui_mainwindow.h"
                                        
                                        #include "QTimer"
                                        #include "QThread"
                                        
                                        void MainWindow::SetupWithProgressbar() {
                                        
                                            ui->progressBar->setValue(20);
                                        
                                            int i;
                                            double result;
                                            QString string;
                                        
                                            for(i = 0;i < 5000000;i++) {
                                        
                                                result = ((((i * 1337) / 7) * 3) - 5) % 1937;
                                        
                                                string = QString::number(result);
                                        
                                                ui->label->setText(string);
                                            }
                                        
                                            ui->progressBar->setValue(80);
                                        }
                                        
                                        MainWindow::MainWindow(QWidget *parent) :
                                            QMainWindow(parent),
                                            ui(new Ui::MainWindow)
                                        {
                                            ui->setupUi(this);
                                        
                                            QTimer::singleShot(10, this, MainWindow::SetupWithProgressbar());
                                        }
                                        
                                        MainWindow::~MainWindow()
                                        {
                                            delete ui;
                                        }
                                        

                                        But I am getting an error:

                                        error: invalid use of void expression
                                             QTimer::singleShot(10, this, MainWindow::SetupWithProgressbar());
                                                                                                ^
                                        

                                        I think it is correct.

                                        @kshegunov said in Function after setupUi():

                                        Here, however I provide no text here as instruction. You need to read what an event loop is, how it relates to the GUI, what blocking the event loop means and how one can process things without blocking the event loop (multiple topics all available in the documentation).

                                        #include <QApplication>
                                        #include <QProgressDialog>
                                        #include <QTimer>
                                        
                                        int main(int argc, char ** argv)
                                        {
                                            QApplication application(argc, argv);
                                        
                                            QTimer timer;
                                            timer.setInterval(100); //< Simulates a long running operation in the background
                                            timer.start();
                                        
                                            QProgressDialog dialog(QStringLiteral("Test dialog"), QStringLiteral("Cancel"), 0, 100);
                                            dialog.show();
                                        
                                            int counter = 0;
                                            QObject::connect(&timer, &QTimer::timeout, &dialog, [&dialog, &timer, &counter] () -> void {
                                                counter++;
                                                if (counter >= dialog.maximum())  {
                                                    timer.stop();
                                                    dialog.close();
                                                    return;
                                                }
                                        
                                                dialog.setValue(counter);
                                            });
                                        
                                            QObject::connect(&dialog, &QProgressDialog::canceled, &timer, &QTimer::stop);
                                            QObject::connect(&dialog, &QProgressDialog::canceled, &application, &QApplication::quit);
                                        
                                            return QApplication::exec();
                                        }
                                        

                                        Isnt it quite complicated for such simple thing? :/

                                        K Offline
                                        K Offline
                                        kshegunov
                                        Moderators
                                        wrote on 7 Feb 2017, 11:30 last edited by
                                        #25

                                        @t0msk said in Function after setupUi():

                                        Isnt it quite complicated for such simple thing? :/

                                        You have a working example in 15-20 lines, so what is the complicated part?

                                        Because I dont understand it, why there is timer?

                                        Because for the example one needs to simulate a long-running operation (as the comment states). In real code the timer would be substituted with a thread to offload the GUI thread and that thread would raise a signal (just like QTimer::timeout) which notifies the GUI thread about the progress.

                                        I am newbie in Qt, so I am looking for simpler solution.

                                        Eh? Can't get simpler than this. You need to read the topics I mentioned. Did you?

                                        I used this in C# and it worked out of box.

                                        Perhaps that's true, I have no knowledge of C# but I really don't see the relevance here. Qt is a C++ library, so if you want to work with C++ you need to stick to C++'s specifics - memory management, threading, etc.

                                        @J.Hilk said in Function after setupUi():

                                        The "proper" way would be to put your "CPU-heavy function" in a different thread and use Signal/Slots to update the UI.

                                        It would.

                                        something along the lines

                                        Your code has one serious drawback, however - you can't stop the operation in the middle if you need for example to quit the application. For this to be feasible one needs to ensure the worker thread's event loop isn't blocked.

                                        Read and abide by the Qt Code of Conduct

                                        1 Reply Last reply
                                        1
                                        • M mrjj
                                          6 Feb 2017, 17:09

                                          @t0msk
                                          His example just makes the dialog have a counter (progress) as to simulate something is going on. like
                                          downloading a patch.
                                          The timer will post a "timeout" to the event loop ( which in this case is NOT blocked) and
                                          the dialog can update and "do stuff"

                                          The syntax
                                          "QObject::connect(&timer, &QTimer::timeout, &dialog, [&dialog, &timer, &counter] () ->"
                                          just creates a function in the spot. So all inside
                                          {
                                          // normal slot code.
                                          }
                                          Is just the code you would put in a normal slot function.
                                          This allows for the logic to be in main and not inside mainwindow.

                                          So the timer allows to draw and update the Progress while for loops do not as easy.

                                          Hope this makes it more clear.

                                          T Offline
                                          T Offline
                                          t0msk
                                          wrote on 7 Feb 2017, 11:34 last edited by
                                          #26

                                          @mrjj said in Function after setupUi():

                                          @t0msk
                                          His example just makes the dialog have a counter (progress) as to simulate something is going on. like
                                          downloading a patch.
                                          The timer will post a "timeout" to the event loop ( which in this case is NOT blocked) and
                                          the dialog can update and "do stuff"

                                          The syntax
                                          "QObject::connect(&timer, &QTimer::timeout, &dialog, [&dialog, &timer, &counter] () ->"
                                          just creates a function in the spot. So all inside
                                          {
                                          // normal slot code.
                                          }
                                          Is just the code you would put in a normal slot function.
                                          This allows for the logic to be in main and not inside mainwindow.

                                          So the timer allows to draw and update the Progress while for loops do not as easy.

                                          Hope this makes it more clear.

                                          Must it be in main? I would like to have code from mainwindow in mainwindow.cpp not in main

                                          @J.Hilk said in Function after setupUi():

                                          I personaly would approach this situation differently from what was suggestet so far.

                                          The "proper" way would be to put your "CPU-heavy function" in a different thread and use Signal/Slots to update the UI.

                                          something along the lines:

                                          *.h:

                                          signals:
                                              void pBarSetValue(int value);
                                              void showResult(QString result);
                                          

                                          *.cpp

                                          ui->setupUi(this);
                                          
                                          connect(this, &MyClass::pBarSetValue, ui->progressBar, QProgressBar::setValue);
                                          connect(this, &MyClass::showResult, ui->label, &QLabel::setText);
                                          
                                          ui->progressBar->setRange(0,5000000);
                                          
                                          
                                          QtConcurrent::run([=]() {
                                              for(i = 0;i < 5000000;i++) {
                                          
                                                    double dResult = ((((i * 1337) / 7) * 3) - 5) % 1937;
                                          
                                                    emit showResult(QString::number(dResult));
                                                    emit pBarSetValue(i);
                                              }
                                          }
                                          

                                          Thank you, so if I understood correctly, emit will "send" signal to function pBarSetValue() and connect will "catch" this signal with value and redirect it to QProgressBar::setValue() ? :)

                                          And QtConcurrent::run() will run function in new thread, yes? So it is same solution like this? :

                                          QThread thread;
                                          moveToThread(&thread);
                                          connect(&thread, SIGNAL(started()), this, SLOT(myfunction()));
                                          thread.start();
                                          

                                          Another question what syntax is this QtConcurrent::run( [ = ] () ? I have never seen anything like this before, and I got an error at the end of function:

                                          error: expected ')' before '}' token
                                           }
                                           ^
                                          

                                          The last question what happens if computer has only 1 thread CPU?

                                          Student who loves C/C++

                                          K jsulmJ 2 Replies Last reply 7 Feb 2017, 11:43
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