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Function after setupUi()

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  • 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
      M Offline
      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.

                K Offline
                K Offline
                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

                1 Reply Last reply
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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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                  • T Offline
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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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                      • T Offline
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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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                          M Offline
                          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.

                            T Offline
                            T Offline
                            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.

                                  M Offline
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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
                                  0
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                                    J Offline
                                    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.

                                    1 Reply Last reply
                                    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
                                        0
                                        • T t0msk
                                          7 Feb 2017, 11:34

                                          @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?

                                          K Offline
                                          K Offline
                                          kshegunov
                                          Moderators
                                          wrote on 7 Feb 2017, 11:43 last edited by
                                          #27

                                          @t0msk said in Function after setupUi():

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

                                          Of course not. I had put it in main only to provide a fully self-contained example. You could put it wherever it suits you as long as the function is executed in the context of the main thread.

                                          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()?

                                          pBarSetValue is the actual signal. Look here: http://doc.qt.io/qt-5/signalsandslots.html

                                          And QtConcurrent::run() will run function in new thread, yes?

                                          Yes.

                                          So it is same solution like this?

                                          It's very similar, yes.

                                          Another question what syntax is this QtConcurrent::run( [ = ] () ?

                                          It's a lambda (anonymous) function. It's part of the C++11 standard. Look here: http://en.cppreference.com/w/cpp/language/lambda

                                          I got an error at the end of function

                                          Because there's a typo at the end of the code - it doesn't close the function arguments' parenthesis. It should be like this:

                                          QtConcurrent::run([=] () {
                                              // ...
                                          });
                                          

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

                                          If you mean you have a single core CPU, then it's the OS's responsibility to switch between the threads (so called context switches) and execute things (by things I mean the assembly) sequentially, but this doesn't directly affect you. From your perspective as a programmer it still looks like the threads are executing in parallel.

                                          Read and abide by the Qt Code of Conduct

                                          1 Reply Last reply
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