Skip to content
  • Categories
  • Recent
  • Tags
  • Popular
  • Users
  • Groups
  • Search
  • Get Qt Extensions
  • Unsolved
Collapse
Brand Logo
  1. Home
  2. Qt Development
  3. General and Desktop
  4. QtFileDialog stocks after until subprocess finished
Forum Updated to NodeBB v4.3 + New Features

QtFileDialog stocks after until subprocess finished

Scheduled Pinned Locked Moved Unsolved General and Desktop
20 Posts 3 Posters 1.4k Views 2 Watching
  • Oldest to Newest
  • Newest to Oldest
  • Most Votes
Reply
  • Reply as topic
Log in to reply
This topic has been deleted. Only users with topic management privileges can see it.
  • ademmlerA Offline
    ademmlerA Offline
    ademmler
    wrote on last edited by
    #1

    Hi there,

    in my application i use

    QString fileName = QFileDialog::getOpenFileName(this,
                                                        tr("Open Input Image"),
                                                        desktopPath,
                                                        tr("Open file") + " (*.jpg *.jpeg *.png *.bmp *.tif *.tiff *.pdf)");
    
    
        if(fileName.isEmpty()) {
             QMessageBox::warning(this, tr("Error"), tr("No input file selcted"));        
             return;
        }
        
       QApplication::processEvents();
        processFile(fileName);
    
        doSomething();
    

    Inside the doSomething() function I use a system call (I tried this two):

    int err = system(cmd.toLatin1().constData());
    QProcess::execute(cmd);
    

    The "FileDialog get stuck - until the subprocess has finished.
    Is there any option or trick to close the "open file dialog" after selecting a file and "ok click" ?

    thx to all

    JonBJ 1 Reply Last reply
    0
    • ademmlerA ademmler

      Hi there,

      in my application i use

      QString fileName = QFileDialog::getOpenFileName(this,
                                                          tr("Open Input Image"),
                                                          desktopPath,
                                                          tr("Open file") + " (*.jpg *.jpeg *.png *.bmp *.tif *.tiff *.pdf)");
      
      
          if(fileName.isEmpty()) {
               QMessageBox::warning(this, tr("Error"), tr("No input file selcted"));        
               return;
          }
          
         QApplication::processEvents();
          processFile(fileName);
      
          doSomething();
      

      Inside the doSomething() function I use a system call (I tried this two):

      int err = system(cmd.toLatin1().constData());
      QProcess::execute(cmd);
      

      The "FileDialog get stuck - until the subprocess has finished.
      Is there any option or trick to close the "open file dialog" after selecting a file and "ok click" ?

      thx to all

      JonBJ Offline
      JonBJ Offline
      JonB
      wrote on last edited by
      #2

      @ademmler

      int err = system(cmd.toLatin1().constData());
      QProcess::execute(cmd);
      

      You are running your OS cmd twice! First, get rid of the system() call, and don't use that again!

      It blocks because you use QProcess::execute(). Assuming as you say (I don't know any different) that the file dialog does not disappear, you need to allow the code to return into the main Qt event loop for it to get removed. You have a couple of possibly approaches:

      • Change to using QProcess::start(), and use the finished etc. signals if you need to know when it finishes. This is probably the best idea.

      • If you want to stick with QProcess::exec() (or QProcess::waitForFinished()), either emit a signal or your own which you have connect()ed with Qt::QueuedConnection as the connection type, or use a QTimer() to put in a tiny delay, and have the slot on either of these do the QProcess::exec().

      1 Reply Last reply
      1
      • ademmlerA Offline
        ademmlerA Offline
        ademmler
        wrote on last edited by ademmler
        #3

        thx, this was not the real code. just the commands I was trying out ;-)
        Here is a better writing.

        Inside the doSomething() function I use a system call (I tried this two):
        
        this "int err = system(cmd.toLatin1().constData());"
        or  this "QProcess::execute(cmd);"
        
        1 Reply Last reply
        0
        • ademmlerA Offline
          ademmlerA Offline
          ademmler
          wrote on last edited by ademmler
          #4

          Ok - I have tried this out:

          Globally I defined: QProcess myProcess

          a) In the subroutine I use: QProcess::start()
          In this case the dialog is still blocked.

          b) If I use: QProcess::startDetached()
          Now the dialog closes as expected.

          In order do wait until this process ist finished I use:
          myProcess.waitForFinished(-1);

          I knew (-1) means - never time out. I use it right now for testing.

          In my case the main routine does not wait for the process to be finished.
          This of course causes more issues than ...

          Finally I tried this suggestion - and it did not work.
          Is this maybe an Mac OS X issue?

          How can I detect securely the state of myProcess ?

          1 Reply Last reply
          0
          • ademmlerA Offline
            ademmlerA Offline
            ademmler
            wrote on last edited by ademmler
            #5

            Her is a minimal example to illustrate the issue.
            http://files.lacunasolutions.com/various/QtMinimal.zip

            Please note this might not work on windows. You may need to change the system call in the subroutine to something else.

            mrjjM 1 Reply Last reply
            0
            • ademmlerA ademmler

              Her is a minimal example to illustrate the issue.
              http://files.lacunasolutions.com/various/QtMinimal.zip

              Please note this might not work on windows. You may need to change the system call in the subroutine to something else.

              mrjjM Offline
              mrjjM Offline
              mrjj
              Lifetime Qt Champion
              wrote on last edited by
              #6

              @ademmler
              Hi
              Dont use myProcess.waitForFinished(-1); as it blocks the GUI.
              Use QProcess finished signal to wait to do rest of code until it sends signal.

              void MainWindow::on_openButton_clicked()
              {
                  ui->statusbar->showMessage("Open file dialog.", 0);
              
                  QString imagePath = QFileDialog::getOpenFileName(
                              this,
                              tr("Open File"),
                              QStandardPaths::writableLocation(QStandardPaths::DesktopLocation),
                              tr("TIFF (*.tif *tiff);;JPEG (*.jpg *.jpeg);;PNG (*.png)" )
                              );
              
                  QApplication::processEvents();
              
                  doSomething(imagePath);
              
                  ui->statusbar->showMessage("Waiting for subprocess to end.", 0);
              
                  connect(&process, QOverload<int, QProcess::ExitStatus>::of(&QProcess::finished), this, [this,imagePath](){
                      ui->statusbar->showMessage("Subprocess ended.", 0);
              
              
                      imageObject = new QImage();
                      imageObject->load(imagePath);
                      image = QPixmap::fromImage(*imageObject);
              
                      scene = new QGraphicsScene(this);
                      pixmap = scene->addPixmap(image);
                      scene->setSceneRect(image.rect());
                      ui->graphicsView->setScene(scene);
              
                      pixmap->setFlag(QGraphicsItem::ItemIsMovable);
                  });
              
              
              }
              
              1 Reply Last reply
              2
              • ademmlerA Offline
                ademmlerA Offline
                ademmler
                wrote on last edited by
                #7

                @mrjj

                Perfect - that fixed the issue.

                How can I access stdout or error messages in this way?

                Would you tell me what do do, if I need to launch multiple sub processes and catch them separate?

                JonBJ 1 Reply Last reply
                0
                • ademmlerA ademmler

                  @mrjj

                  Perfect - that fixed the issue.

                  How can I access stdout or error messages in this way?

                  Would you tell me what do do, if I need to launch multiple sub processes and catch them separate?

                  JonBJ Offline
                  JonBJ Offline
                  JonB
                  wrote on last edited by JonB
                  #8

                  @ademmler

                  How can I access stdout or error messages in this way?

                  Search the https://doc.qt.io/qt-5/qprocess.html docs page for stdout, stderr etc.

                  Would you tell me what do do, if I need to launch multiple sub processes and catch them separate?

                  Just create separate QProcess instances.

                  ademmlerA 1 Reply Last reply
                  0
                  • JonBJ JonB

                    @ademmler

                    How can I access stdout or error messages in this way?

                    Search the https://doc.qt.io/qt-5/qprocess.html docs page for stdout, stderr etc.

                    Would you tell me what do do, if I need to launch multiple sub processes and catch them separate?

                    Just create separate QProcess instances.

                    ademmlerA Offline
                    ademmlerA Offline
                    ademmler
                    wrote on last edited by
                    #9

                    @JonB

                    thx for telling me - I read this all day ... but still it did not work d for me ...

                    JonBJ 1 Reply Last reply
                    0
                    • ademmlerA ademmler

                      @JonB

                      thx for telling me - I read this all day ... but still it did not work d for me ...

                      JonBJ Offline
                      JonBJ Offline
                      JonB
                      wrote on last edited by
                      #10

                      @ademmler
                      Glancing at sample code https://gist.github.com/ynonp/8148340, this should work, and give you the idea of what is needed.

                      ademmlerA 1 Reply Last reply
                      1
                      • JonBJ JonB

                        @ademmler
                        Glancing at sample code https://gist.github.com/ynonp/8148340, this should work, and give you the idea of what is needed.

                        ademmlerA Offline
                        ademmlerA Offline
                        ademmler
                        wrote on last edited by
                        #11

                        @JonB

                        thx for pointing me to a working example.

                        1 Reply Last reply
                        0
                        • ademmlerA Offline
                          ademmlerA Offline
                          ademmler
                          wrote on last edited by ademmler
                          #12

                          @mrjj said in QtFileDialog stocks after until subprocess finished:

                          );

                          connect(&process, QOverload<int, QProcess::ExitStatus>::of(&QProcess::finished), this, [this,imagePath](){
                              ui->statusbar->showMessage("Subprocess ended.", 0
                          

                          I used this and it works fine so far - the blocked dialog gets free ...
                          But I am wondering how I can pause the whole application until this thread is finished.

                          Using process.waitForFinish() did not work here ...

                          What I want to achieve is - a free dialog, a progress bar telling me
                          that something is going on and at when all processes have end the image will be displayed and progress bar is stopped.

                          mrjjM 1 Reply Last reply
                          0
                          • ademmlerA ademmler

                            @mrjj said in QtFileDialog stocks after until subprocess finished:

                            );

                            connect(&process, QOverload<int, QProcess::ExitStatus>::of(&QProcess::finished), this, [this,imagePath](){
                                ui->statusbar->showMessage("Subprocess ended.", 0
                            

                            I used this and it works fine so far - the blocked dialog gets free ...
                            But I am wondering how I can pause the whole application until this thread is finished.

                            Using process.waitForFinish() did not work here ...

                            What I want to achieve is - a free dialog, a progress bar telling me
                            that something is going on and at when all processes have end the image will be displayed and progress bar is stopped.

                            mrjjM Offline
                            mrjjM Offline
                            mrjj
                            Lifetime Qt Champion
                            wrote on last edited by mrjj
                            #13

                            @ademmler said in QtFileDialog stocks after until subprocess finished:

                            But I am wondering how I can pause the whole application until this thread is finished.

                            You dont pause a GUI app. That is simply wrong thinking.
                            Most of Qt classes work with signal and slot.

                            So when you do something, you simply hook up to a signal and then when the signal comes, you
                            do what you need.

                            So often you have to split the code in 2 parts.
                            The setup part
                            and the processing part where you react to the signal.

                            You cannot pause an app. It will stop drawing and turns white etc.

                            and don't use waitForFinish as it hangs the app. really not a good idea in GUI apps. ever.

                            so just use signals and slots and the app will do nothing until some signal comes and then you
                            do what you need in the slot.

                            ademmlerA 1 Reply Last reply
                            2
                            • mrjjM mrjj

                              @ademmler said in QtFileDialog stocks after until subprocess finished:

                              But I am wondering how I can pause the whole application until this thread is finished.

                              You dont pause a GUI app. That is simply wrong thinking.
                              Most of Qt classes work with signal and slot.

                              So when you do something, you simply hook up to a signal and then when the signal comes, you
                              do what you need.

                              So often you have to split the code in 2 parts.
                              The setup part
                              and the processing part where you react to the signal.

                              You cannot pause an app. It will stop drawing and turns white etc.

                              and don't use waitForFinish as it hangs the app. really not a good idea in GUI apps. ever.

                              so just use signals and slots and the app will do nothing until some signal comes and then you
                              do what you need in the slot.

                              ademmlerA Offline
                              ademmlerA Offline
                              ademmler
                              wrote on last edited by
                              #14

                              @mrjj

                              Ok - thank your for clearing this - hence I need to get into slots and signals concept ...

                              mrjjM 1 Reply Last reply
                              0
                              • ademmlerA ademmler

                                @mrjj

                                Ok - thank your for clearing this - hence I need to get into slots and signals concept ...

                                mrjjM Offline
                                mrjjM Offline
                                mrjj
                                Lifetime Qt Champion
                                wrote on last edited by
                                #15

                                @ademmler
                                Yes its a must use with Qt :)
                                At least when its a GUI app.

                                1 Reply Last reply
                                0
                                • ademmlerA Offline
                                  ademmlerA Offline
                                  ademmler
                                  wrote on last edited by
                                  #16

                                  Hello guys,

                                  I have a conceptional question about Signals and slots which I could not find an answer.

                                  1. Lets say I launch 2 processes one directly after the other.

                                  2. Process A is much slower than process B.

                                  3. I need to wait for Process A (and his slot subtasks) to be finished before I execute the "slot" of process B.

                                  How can I achieve this?

                                  mrjjM JonBJ 2 Replies Last reply
                                  0
                                  • ademmlerA ademmler

                                    Hello guys,

                                    I have a conceptional question about Signals and slots which I could not find an answer.

                                    1. Lets say I launch 2 processes one directly after the other.

                                    2. Process A is much slower than process B.

                                    3. I need to wait for Process A (and his slot subtasks) to be finished before I execute the "slot" of process B.

                                    How can I achieve this?

                                    mrjjM Offline
                                    mrjjM Offline
                                    mrjj
                                    Lifetime Qt Champion
                                    wrote on last edited by
                                    #17

                                    @ademmler
                                    Hi
                                    I assume you mean 2 x QProcess ?

                                    You would simply hook up to A and when it says finished you
                                    call the B slot.

                                    Or do you mean inside B, it needs to wait for A ?

                                    If you just mean inside the app, then you can just use A signal and then
                                    do what you need to do as B should be finished long time ago.

                                    1 Reply Last reply
                                    1
                                    • ademmlerA ademmler

                                      Hello guys,

                                      I have a conceptional question about Signals and slots which I could not find an answer.

                                      1. Lets say I launch 2 processes one directly after the other.

                                      2. Process A is much slower than process B.

                                      3. I need to wait for Process A (and his slot subtasks) to be finished before I execute the "slot" of process B.

                                      How can I achieve this?

                                      JonBJ Offline
                                      JonBJ Offline
                                      JonB
                                      wrote on last edited by
                                      #18

                                      @ademmler said in QtFileDialog stocks after until subprocess finished:

                                      I need to wait for Process A (and his slot subtasks) to be finished before I execute the "slot" of process B.

                                      Maybe you mean you could/should not start process B until process A is finished? Saying you don't want to execute a slot connected to process B until after those of process A seems strange.

                                      1 Reply Last reply
                                      1
                                      • ademmlerA Offline
                                        ademmlerA Offline
                                        ademmler
                                        wrote on last edited by
                                        #19

                                        To go deeper into it.

                                        1. The reason is, that the time of the processes is always unknown and different. Hence I do not know how long each run of the app a process will take.

                                        2. The only rule is A has to follow B

                                        Isn't there any clear signal when a connect has taken place and when the related tasks are done?

                                        Can I emit another Signal with in a "connection" ?

                                        Regards Alexander

                                        JonBJ 1 Reply Last reply
                                        0
                                        • ademmlerA ademmler

                                          To go deeper into it.

                                          1. The reason is, that the time of the processes is always unknown and different. Hence I do not know how long each run of the app a process will take.

                                          2. The only rule is A has to follow B

                                          Isn't there any clear signal when a connect has taken place and when the related tasks are done?

                                          Can I emit another Signal with in a "connection" ?

                                          Regards Alexander

                                          JonBJ Offline
                                          JonBJ Offline
                                          JonB
                                          wrote on last edited by
                                          #20

                                          @ademmler said in QtFileDialog stocks after until subprocess finished:

                                          Isn't there any clear signal when a connect has taken place and when the related tasks are done?

                                          What "related tasks are done"? You have seen there is a QProcess::finished signal. If you want to only start B after A has finished, use that.

                                          1 Reply Last reply
                                          2

                                          • Login

                                          • Login or register to search.
                                          • First post
                                            Last post
                                          0
                                          • Categories
                                          • Recent
                                          • Tags
                                          • Popular
                                          • Users
                                          • Groups
                                          • Search
                                          • Get Qt Extensions
                                          • Unsolved