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Updating c++ data in Qml

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  • jsulmJ jsulm

    @dziko147 said in Updating c++ data in Qml:

    If I don't create MainWindow instance, how can i access to mainwindow variable from UploadCSV.

    Don't create a SECOND MainWindow instance! Use the one you already have (you probably create it in main.cpp, right?)...

    D Offline
    D Offline
    dziko147
    wrote on last edited by
    #29

    @jsulm Yes sure . so I use it ?

    jsulmJ 1 Reply Last reply
    0
    • D dziko147

      @jsulm Yes sure . so I use it ?

      jsulmJ Offline
      jsulmJ Offline
      jsulm
      Lifetime Qt Champion
      wrote on last edited by
      #30

      @dziko147 said in Updating c++ data in Qml:

      so I use it ?

      Yes, the one you already have

      https://forum.qt.io/topic/113070/qt-code-of-conduct

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      • D Offline
        D Offline
        dziko147
        wrote on last edited by
        #31

        @KroMignon Is this code correct ??

        I create a class member :

        class MainWindow : public QMainWindow
        {
            Q_OBJECT
        public:
            Backend *back;
        

        then in uploadCSV.cpp

          connect(ui->parambtn_2, SIGNAL(clicked()),MainWindow().back, SLOT(statuspican()),Qt::QueuedConnection);
        
        

        But still doesn't work !

        jsulmJ 1 Reply Last reply
        0
        • D dziko147

          @KroMignon Is this code correct ??

          I create a class member :

          class MainWindow : public QMainWindow
          {
              Q_OBJECT
          public:
              Backend *back;
          

          then in uploadCSV.cpp

            connect(ui->parambtn_2, SIGNAL(clicked()),MainWindow().back, SLOT(statuspican()),Qt::QueuedConnection);
          
          

          But still doesn't work !

          jsulmJ Offline
          jsulmJ Offline
          jsulm
          Lifetime Qt Champion
          wrote on last edited by
          #32

          @dziko147 said in Updating c++ data in Qml:

          connect(ui->parambtn_2, SIGNAL(clicked()),MainWindow().back, SLOT(statuspican()),Qt::QueuedConnection);

          You're creating a new MainWindow instance in the connect.
          I give up...

          https://forum.qt.io/topic/113070/qt-code-of-conduct

          D 1 Reply Last reply
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          • jsulmJ jsulm

            @dziko147 said in Updating c++ data in Qml:

            connect(ui->parambtn_2, SIGNAL(clicked()),MainWindow().back, SLOT(statuspican()),Qt::QueuedConnection);

            You're creating a new MainWindow instance in the connect.
            I give up...

            D Offline
            D Offline
            dziko147
            wrote on last edited by
            #33

            @jsulm Sorry :( :( :(
            why you don't/want give an example ?
            I can understand you with example :)

            jsulmJ 1 Reply Last reply
            0
            • D dziko147

              @jsulm Sorry :( :( :(
              why you don't/want give an example ?
              I can understand you with example :)

              jsulmJ Offline
              jsulmJ Offline
              jsulm
              Lifetime Qt Champion
              wrote on last edited by jsulm
              #34

              @dziko147 You should really learn C++ basics first before you continue with Qt.
              This is now second thread from you where people are trying to explain to you what you are doing wrong. Your problem is not Qt but missing C++ knowledge.

              For example: why did you write "MainWindow()" bellow? Do you know what MainWindow() does? And how does this relate to what I wrote (use existing MainWindow instance)? You again create a new MainWindow instance, even if you was told many times to not to do so!

              connect(ui->parambtn_2, SIGNAL(clicked()),MainWindow().back, SLOT(statuspican()),Qt::QueuedConnection);
              

              https://forum.qt.io/topic/113070/qt-code-of-conduct

              D 1 Reply Last reply
              0
              • jsulmJ jsulm

                @dziko147 You should really learn C++ basics first before you continue with Qt.
                This is now second thread from you where people are trying to explain to you what you are doing wrong. Your problem is not Qt but missing C++ knowledge.

                For example: why did you write "MainWindow()" bellow? Do you know what MainWindow() does? And how does this relate to what I wrote (use existing MainWindow instance)? You again create a new MainWindow instance, even if you was told many times to not to do so!

                connect(ui->parambtn_2, SIGNAL(clicked()),MainWindow().back, SLOT(statuspican()),Qt::QueuedConnection);
                
                D Offline
                D Offline
                dziko147
                wrote on last edited by
                #35

                @jsulm ok told me how to do this . I am a student in first year . So i am already learning :/ .
                Yes I understand that i create a second instance but i haven't another choice . the only solution for me is to ask you . :(

                jsulmJ 1 Reply Last reply
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                • D dziko147

                  @jsulm ok told me how to do this . I am a student in first year . So i am already learning :/ .
                  Yes I understand that i create a second instance but i haven't another choice . the only solution for me is to ask you . :(

                  jsulmJ Offline
                  jsulmJ Offline
                  jsulm
                  Lifetime Qt Champion
                  wrote on last edited by
                  #36

                  @dziko147 said in Updating c++ data in Qml:

                  Yes I understand that i create a second instance

                  You need to understand that it is quite disappointing for others to repeat the same thing again and again and again and then see that you are still doing EXACTLY the same mistake even if you know that it is wrong! So, why do you again post code which is wrong if you know that it is wrong?

                  I can't tell you how exactly you need to do it because I don't have your code and so don't know how it is structured...
                  From architectural point of view it is strange why uploadCSV should connect a signal to a slot in a member variable in another class? uploadCSV should not even know that MainWindow has a member called "back". This was already pointed out by @SGaist

                  Where is the uploadCSV instance created? Does MainWindow create it?

                  https://forum.qt.io/topic/113070/qt-code-of-conduct

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                  • D Offline
                    D Offline
                    dziko147
                    wrote on last edited by
                    #37

                    @jsulm this is my situation.

                    My project compouned of 3 classes :
                    1/Mainwindow
                    2/backend
                    /UploadCSV
                    In Mainwindow :
                    1/ I have a quickwidget which integrate a qml file .
                    2/ I create a backend instance to get data from it and fill the QMl File

                    In Backend
                    1/I have the defenition of my data (getter, setter, change slots).

                    In UploadCSV
                    1/I have a button when it's clicked a slot in Backend will change some data .
                    2/After change data I would like to display it on QML .

                    I hope it's clear

                    jsulmJ 1 Reply Last reply
                    0
                    • D dziko147

                      @jsulm this is my situation.

                      My project compouned of 3 classes :
                      1/Mainwindow
                      2/backend
                      /UploadCSV
                      In Mainwindow :
                      1/ I have a quickwidget which integrate a qml file .
                      2/ I create a backend instance to get data from it and fill the QMl File

                      In Backend
                      1/I have the defenition of my data (getter, setter, change slots).

                      In UploadCSV
                      1/I have a button when it's clicked a slot in Backend will change some data .
                      2/After change data I would like to display it on QML .

                      I hope it's clear

                      jsulmJ Offline
                      jsulmJ Offline
                      jsulm
                      Lifetime Qt Champion
                      wrote on last edited by
                      #38

                      @dziko147 said in Updating c++ data in Qml:

                      I hope it's clear

                      No, you did not answer my question, which is actually quite clear...

                      https://forum.qt.io/topic/113070/qt-code-of-conduct

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                      • D Offline
                        D Offline
                        dziko147
                        wrote on last edited by
                        #39

                        I give uuuuuuuuuuuuuup

                        1 Reply Last reply
                        0
                        • J.HilkJ Offline
                          J.HilkJ Offline
                          J.Hilk
                          Moderators
                          wrote on last edited by
                          #40

                          alright @jsulm
                          alt text

                          @dziko147 this does actually help

                          My project compouned of 3 classes :
                          1/Mainwindow
                          2/backend
                          /UploadCSV
                          In Mainwindow :
                          1/ I have a quickwidget which integrate a qml file .
                          2/ I create a backend instance to get data from it and fill the QMl File

                          In Backend
                          1/I have the defenition of my data (getter, setter, change slots).

                          In UploadCSV
                          1/I have a button when it's clicked a slot in Backend will change some data .
                          2/After change data I would like to display it on QML .

                          I hope it's clear

                          some more required information:

                          • how do you expose backend to the qml context, and where (in your code)
                          • name of your backend and uploadcsv instances, and where they are defined
                          • does UploadCSV have its own UI components? do you mean that with "button"

                          I have the high suspicion that everything is centered in and around mainwindow already and its only a matter of connecting it. But truthfully code will help, it doesn't look like you have much yet, so post as much as you can


                          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.

                          D 1 Reply Last reply
                          2
                          • J.HilkJ J.Hilk

                            alright @jsulm
                            alt text

                            @dziko147 this does actually help

                            My project compouned of 3 classes :
                            1/Mainwindow
                            2/backend
                            /UploadCSV
                            In Mainwindow :
                            1/ I have a quickwidget which integrate a qml file .
                            2/ I create a backend instance to get data from it and fill the QMl File

                            In Backend
                            1/I have the defenition of my data (getter, setter, change slots).

                            In UploadCSV
                            1/I have a button when it's clicked a slot in Backend will change some data .
                            2/After change data I would like to display it on QML .

                            I hope it's clear

                            some more required information:

                            • how do you expose backend to the qml context, and where (in your code)
                            • name of your backend and uploadcsv instances, and where they are defined
                            • does UploadCSV have its own UI components? do you mean that with "button"

                            I have the high suspicion that everything is centered in and around mainwindow already and its only a matter of connecting it. But truthfully code will help, it doesn't look like you have much yet, so post as much as you can

                            D Offline
                            D Offline
                            dziko147
                            wrote on last edited by
                            #41

                            @J-Hilk
                            1/ I expose backend to qml like this :

                            back= new Backend();
                                m_ui->quickWidget->setVisible(true);
                                m_ui->quickWidget->rootContext()->setContextProperty("cppObject",back);
                                m_ui->quickWidget->setResizeMode(QQuickWidget::SizeRootObjectToView);
                                m_ui->quickWidget->setSource(QUrl(QStringLiteral("qrc:/qml/automotive.qml")));
                            

                            2/ And UploadCSV in MainWindow just for show . I dont use UploadCSV in MainWindow

                            //BTW CAN i define the connect signal of UploadCSV button here ?
                            void MainWindow::on_actionUpload_CSV_File_triggered()
                            {
                                uploadcsv = new UploadCSV();
                                uploadcsv->show();
                            }
                            

                            3/ Yes Sure UploadCSV has a UI form .

                            J.HilkJ 1 Reply Last reply
                            0
                            • D dziko147

                              @J-Hilk
                              1/ I expose backend to qml like this :

                              back= new Backend();
                                  m_ui->quickWidget->setVisible(true);
                                  m_ui->quickWidget->rootContext()->setContextProperty("cppObject",back);
                                  m_ui->quickWidget->setResizeMode(QQuickWidget::SizeRootObjectToView);
                                  m_ui->quickWidget->setSource(QUrl(QStringLiteral("qrc:/qml/automotive.qml")));
                              

                              2/ And UploadCSV in MainWindow just for show . I dont use UploadCSV in MainWindow

                              //BTW CAN i define the connect signal of UploadCSV button here ?
                              void MainWindow::on_actionUpload_CSV_File_triggered()
                              {
                                  uploadcsv = new UploadCSV();
                                  uploadcsv->show();
                              }
                              

                              3/ Yes Sure UploadCSV has a UI form .

                              J.HilkJ Offline
                              J.HilkJ Offline
                              J.Hilk
                              Moderators
                              wrote on last edited by
                              #42

                              @dziko147 alright,

                              we are getting closer,

                              I assume this:

                              back= new Backend();
                                  m_ui->quickWidget->setVisible(true);
                                  m_ui->quickWidget->rootContext()->setContextProperty("cppObject",back);
                                  m_ui->quickWidget->setResizeMode(QQuickWidget::SizeRootObjectToView);
                                  m_ui->quickWidget->setSource(QUrl(QStringLiteral("qrc:/qml/automotive.qml")));
                              

                              is inside the MainWindow constructor ?

                              //BTW CAN i define the connect signal of UploadCSV button here ?
                              void MainWindow::on_actionUpload_CSV_File_triggered()
                              {
                                  uploadcsv = new UploadCSV();
                                  uploadcsv->show();
                              }
                              

                              The way you have it currently set up, you have to make the connect call here.

                              but that won't work quite yet.

                              • I assume the button you want to press, to update your backend is part of the UploadCSV ui ? Therefore ui->parambtn_2 is the button you want to press and is part of the UploadCSV ui?
                              • have you yet defined a (custom)signal inside the UploadCSV class ?

                              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
                              0
                              • J.HilkJ Offline
                                J.HilkJ Offline
                                J.Hilk
                                Moderators
                                wrote on last edited by J.Hilk
                                #43

                                If my assumptions are correct, I'm writing this before a response,

                                you can/should make the following changes:

                                inside UploadCSV .h add a custom signal, for example purpose we'll name it myCustomButtonClicked(),

                                public:
                                    explicit UploadCSV(QObject *parent = nullptr);
                                .....
                                
                                signals:
                                      void myCustomButtonClicked();
                                
                                

                                inside UploadCSV.cpp constructor definition, after ui->setupUi(this), connect the button to the recently created signal:

                                {
                                    ui->setupUi(this);
                                    connect(ui->parambtn_2, &QAbstractButton::clicked, this, &UploadCSV::myCustomButtonClicked); // this connects/forwards the button clicked signal to the  class signal 'myCustomButtonClicked'
                                }
                                

                                in mainwindow constructor, instantiate the UploadCSV in the constructor and connect it to the backend:

                                {
                                    ui->setupUi(this);
                                back= new Backend();
                                    m_ui->quickWidget->setVisible(true);
                                    m_ui->quickWidget->rootContext()->setContextProperty("cppObject",back);
                                    m_ui->quickWidget->setResizeMode(QQuickWidget::SizeRootObjectToView);
                                    m_ui->quickWidget->setSource(QUrl(QStringLiteral("qrc:/qml/automotive.qml")));
                                
                                uploadcsv = new UploadCSV();
                                connect(uploadcsv, & UploadCSV:: myCustomButtonClicked, backend, &Backend::status); //status has to be public!
                                
                                }
                                

                                your on_actionUpload_CSV_File_triggered now only contains this:

                                void MainWindow::on_actionUpload_CSV_File_triggered()
                                {
                                    uploadcsv->show();
                                }
                                

                                let's see if that worked.

                                code my contain typos, so be aware :D


                                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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                                • D Offline
                                  D Offline
                                  dziko147
                                  wrote on last edited by
                                  #44

                                  @J-Hilk said in Updating c++ data in Qml:

                                  If my assumptions are correct, I'm writing this before a response,

                                  Finally it works :D :D :D
                                  téléchargement (1).jpg

                                  J.HilkJ 1 Reply Last reply
                                  1
                                  • D Offline
                                    D Offline
                                    dziko147
                                    wrote on last edited by
                                    #45

                                    And thanks @KroMignon @jsulm thank you for the effort you made for me

                                    1 Reply Last reply
                                    2
                                    • D dziko147

                                      @J-Hilk said in Updating c++ data in Qml:

                                      If my assumptions are correct, I'm writing this before a response,

                                      Finally it works :D :D :D
                                      téléchargement (1).jpg

                                      J.HilkJ Offline
                                      J.HilkJ Offline
                                      J.Hilk
                                      Moderators
                                      wrote on last edited by
                                      #46

                                      @dziko147 WUHUH congrats!

                                      If you would be so kind and use the topic tool button and set the topic to solved :D


                                      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
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