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accessing aggregates (QVector of a struct)

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  • fcarneyF Offline
    fcarneyF Offline
    fcarney
    wrote on last edited by fcarney
    #12
    Repeater {
      model: changeConsumablesViewModel.getBottleListQv() // or use property, a property will have a signal to update if the list changes
      Bottle {
        cellText: modelData.name
      }
    }
    

    If you want more interaction then a model might be more appropriate.

    modelData Search for modelData on that page to understand where it comes from.

    C++ is a perfectly valid school of magic.

    mzimmersM 1 Reply Last reply
    0
    • kshegunovK kshegunov

      You can refer to the object by id. Like this:

      function loadRackDataFirst() {
          bottle1.cellText = changeConsumablesViewModel.getBottleListQv()[0].name
      }
      

      However you should convert to QString.

      mzimmersM Offline
      mzimmersM Offline
      mzimmers
      wrote on last edited by
      #13

      @kshegunov the "name" field isn't accessible as I've currently implemented it. I think I may have over-designed this. I've made several changes since my earlier posts, so let me recap my code:

      The struct:

      struct BottleData {
        Q_GADGET
      public:
        uint32_t m_volume;               // amount in bottle (in uL)
        uint32_t m_amountNeeded;         // amount needed for synth (in uL)
        int m_position;                  // still figuring this one out
        std::string m_name;              // name of the reagent
        ReagentBottleType m_bottleType;  // bottle type.
        Q_PROPERTY(uint32_t volume MEMBER m_volume)
        Q_PROPERTY(uint32_t amountNeeded MEMBER m_amountNeeded)
        Q_PROPERTY(int position MEMBER m_position)
        Q_PROPERTY(std::string name MEMBER m_name)
        Q_PROPERTY(ReagentBottleType bottleType MEMBER m_bottleType)
      };
      Q_DECLARE_METATYPE(BottleData)
      

      The class:

      typedef QVector<BottleData> BottleDataList;
      
      class BottleList : public QObject
      {
          Q_OBJECT
      private:
          BottleDataList m_bottleList;
      public:
          explicit BottleList(QObject *parent = nullptr);
          Q_PROPERTY(QVariantList qvl READ getBottleListQv)
          QVariantList getBottleListQv();
          ...
      

      From reading the docs, I was under the impression that I wouldn't need a getter for the fields in the struct, because I used the MEMBER macro. Did I misinterpret this?

      fcarneyF kshegunovK 2 Replies Last reply
      0
      • fcarneyF fcarney
        Repeater {
          model: changeConsumablesViewModel.getBottleListQv() // or use property, a property will have a signal to update if the list changes
          Bottle {
            cellText: modelData.name
          }
        }
        

        If you want more interaction then a model might be more appropriate.

        modelData Search for modelData on that page to understand where it comes from.

        mzimmersM Offline
        mzimmersM Offline
        mzimmers
        wrote on last edited by mzimmers
        #14

        @fcarney that looks really powerful. The complete definition of each model is like this:

                Bottle {
                    id: bottle1
                    cellX: 25
                    cellY: 105
                    cellHeight: 75
                    cellWidth: 75
                    bottleScaleFactor: scaleFactor
                    cellText: "W7"
                    cellColor: "red"
                }
        

        If I use the repeater to load the names, can I alter the individual bottles afterwards?

        Thanks...

        PS: I'm aware that there's a lot of ugly hard-coding in here; I was going to address that after I got the connections working.

        1 Reply Last reply
        0
        • fcarneyF Offline
          fcarneyF Offline
          fcarney
          wrote on last edited by fcarney
          #15

          If I use the repeater to load the names, can I alter the individual bottles afterwards?

          It only alters the copy given to the Repeater. It has no way to get that data back.

          I have not used Q_GADGETs before. What does it print out when you console.log(modelData)? Curious as what QML thinks that objects is.

          C++ is a perfectly valid school of magic.

          mzimmersM 1 Reply Last reply
          0
          • mzimmersM mzimmers

            @kshegunov the "name" field isn't accessible as I've currently implemented it. I think I may have over-designed this. I've made several changes since my earlier posts, so let me recap my code:

            The struct:

            struct BottleData {
              Q_GADGET
            public:
              uint32_t m_volume;               // amount in bottle (in uL)
              uint32_t m_amountNeeded;         // amount needed for synth (in uL)
              int m_position;                  // still figuring this one out
              std::string m_name;              // name of the reagent
              ReagentBottleType m_bottleType;  // bottle type.
              Q_PROPERTY(uint32_t volume MEMBER m_volume)
              Q_PROPERTY(uint32_t amountNeeded MEMBER m_amountNeeded)
              Q_PROPERTY(int position MEMBER m_position)
              Q_PROPERTY(std::string name MEMBER m_name)
              Q_PROPERTY(ReagentBottleType bottleType MEMBER m_bottleType)
            };
            Q_DECLARE_METATYPE(BottleData)
            

            The class:

            typedef QVector<BottleData> BottleDataList;
            
            class BottleList : public QObject
            {
                Q_OBJECT
            private:
                BottleDataList m_bottleList;
            public:
                explicit BottleList(QObject *parent = nullptr);
                Q_PROPERTY(QVariantList qvl READ getBottleListQv)
                QVariantList getBottleListQv();
                ...
            

            From reading the docs, I was under the impression that I wouldn't need a getter for the fields in the struct, because I used the MEMBER macro. Did I misinterpret this?

            fcarneyF Offline
            fcarneyF Offline
            fcarney
            wrote on last edited by fcarney
            #16

            @mzimmers said in accessing aggregates (QVector of a struct):

            From reading the docs, I was under the impression that I wouldn't need a getter for the fields in the struct, because I used the MEMBER macro. Did I misinterpret this?

            I "think" so. DOH! I meant to agree to the MEMBER macro doing that, not you misinterpreting this.

            C++ is a perfectly valid school of magic.

            1 Reply Last reply
            0
            • fcarneyF fcarney

              If I use the repeater to load the names, can I alter the individual bottles afterwards?

              It only alters the copy given to the Repeater. It has no way to get that data back.

              I have not used Q_GADGETs before. What does it print out when you console.log(modelData)? Curious as what QML thinks that objects is.

              mzimmersM Offline
              mzimmersM Offline
              mzimmers
              wrote on last edited by
              #17

              @fcarney my console.log isn't working for this app, so I can't tell you. I discovered Q_GADGET from some online searching; in simplest terms, it's a lightweight version of Q_OBJECT (no signals/slots).

              I'm not at all concerned with updating anything other than my display. But now you have me wondering where I should really define all those values. (I would rather not use JSON, but that's probably the right way to do this.)

              fcarneyF 1 Reply Last reply
              0
              • mzimmersM mzimmers

                @fcarney my console.log isn't working for this app, so I can't tell you. I discovered Q_GADGET from some online searching; in simplest terms, it's a lightweight version of Q_OBJECT (no signals/slots).

                I'm not at all concerned with updating anything other than my display. But now you have me wondering where I should really define all those values. (I would rather not use JSON, but that's probably the right way to do this.)

                fcarneyF Offline
                fcarneyF Offline
                fcarney
                wrote on last edited by fcarney
                #18

                @mzimmers If you want your display to interact with the data then a full blown QAbstractListModel would be a better fit. Then each piece of the BottleData object could be its own role. With a setData routine you can edit that model.

                C++ is a perfectly valid school of magic.

                1 Reply Last reply
                0
                • mzimmersM mzimmers

                  @kshegunov the "name" field isn't accessible as I've currently implemented it. I think I may have over-designed this. I've made several changes since my earlier posts, so let me recap my code:

                  The struct:

                  struct BottleData {
                    Q_GADGET
                  public:
                    uint32_t m_volume;               // amount in bottle (in uL)
                    uint32_t m_amountNeeded;         // amount needed for synth (in uL)
                    int m_position;                  // still figuring this one out
                    std::string m_name;              // name of the reagent
                    ReagentBottleType m_bottleType;  // bottle type.
                    Q_PROPERTY(uint32_t volume MEMBER m_volume)
                    Q_PROPERTY(uint32_t amountNeeded MEMBER m_amountNeeded)
                    Q_PROPERTY(int position MEMBER m_position)
                    Q_PROPERTY(std::string name MEMBER m_name)
                    Q_PROPERTY(ReagentBottleType bottleType MEMBER m_bottleType)
                  };
                  Q_DECLARE_METATYPE(BottleData)
                  

                  The class:

                  typedef QVector<BottleData> BottleDataList;
                  
                  class BottleList : public QObject
                  {
                      Q_OBJECT
                  private:
                      BottleDataList m_bottleList;
                  public:
                      explicit BottleList(QObject *parent = nullptr);
                      Q_PROPERTY(QVariantList qvl READ getBottleListQv)
                      QVariantList getBottleListQv();
                      ...
                  

                  From reading the docs, I was under the impression that I wouldn't need a getter for the fields in the struct, because I used the MEMBER macro. Did I misinterpret this?

                  kshegunovK Offline
                  kshegunovK Offline
                  kshegunov
                  Moderators
                  wrote on last edited by kshegunov
                  #19

                  @mzimmers said in accessing aggregates (QVector of a struct):

                  Q_DECLARE_METATYPE(BottleData)
                  

                  is already done by the Q_GADGET so it's superfluous.

                  Switch

                  std::string m_name;
                  

                  to QString.

                  Register the type with QML (qmlRegisterType) if you intend to create instances of it from there.

                  From reading the docs, I was under the impression that I wouldn't need a getter for the fields in the struct, because I used the MEMBER macro. Did I misinterpret this?

                  Nope, this is correct as far as I recall.

                  If I use the repeater to load the names, can I alter the individual bottles afterwards?

                  I don't think so, but I'm a noobster with QML. I believe you can imperatively create the items like this (untested):

                  Component {
                          id: component
                          Bottle { cellText: "default text" }
                          onCompleted: changeConsumablesViewModel.getBottleListQv().forEach(element => function(element)  {
                             createObject(parentItemId, { cellText: element.name });
                          }, this);
                  }
                  

                  or something akin.

                  Read and abide by the Qt Code of Conduct

                  1 Reply Last reply
                  0
                  • mzimmersM Offline
                    mzimmersM Offline
                    mzimmers
                    wrote on last edited by
                    #20

                    OK, so why doesn't this work?

                        Rectangle {
                            id: rack
                            function getBottleName(i) {
                                return changeConsumablesViewModel.getBottleListQv()[i].m_name
                            }
                            Bottle {
                                cellText: rack.getBottleName(0)// "W7"
                            }
                    

                    I get this error on the line with the "return" statement:

                    TypeError: Cannot read property 'm_name' of undefined

                    kshegunovK 1 Reply Last reply
                    0
                    • mzimmersM mzimmers

                      OK, so why doesn't this work?

                          Rectangle {
                              id: rack
                              function getBottleName(i) {
                                  return changeConsumablesViewModel.getBottleListQv()[i].m_name
                              }
                              Bottle {
                                  cellText: rack.getBottleName(0)// "W7"
                              }
                      

                      I get this error on the line with the "return" statement:

                      TypeError: Cannot read property 'm_name' of undefined

                      kshegunovK Offline
                      kshegunovK Offline
                      kshegunov
                      Moderators
                      wrote on last edited by
                      #21

                      @mzimmers said in accessing aggregates (QVector of a struct):

                      TypeError: Cannot read property 'm_name' of undefined

                      Your property is called name, also check the elements you get in that array. Side note: you may need to wait for the component to be fully loaded before doing that (but take with a grain of salt).

                      Read and abide by the Qt Code of Conduct

                      mzimmersM 1 Reply Last reply
                      1
                      • kshegunovK kshegunov

                        @mzimmers said in accessing aggregates (QVector of a struct):

                        TypeError: Cannot read property 'm_name' of undefined

                        Your property is called name, also check the elements you get in that array. Side note: you may need to wait for the component to be fully loaded before doing that (but take with a grain of salt).

                        mzimmersM Offline
                        mzimmersM Offline
                        mzimmers
                        wrote on last edited by
                        #22

                        @kshegunov said in accessing aggregates (QVector of a struct):

                        @mzimmers said in accessing aggregates (QVector of a struct):

                        TypeError: Cannot read property 'm_name' of undefined

                        Your property is called name, also check the elements you get in that array.

                        Tried with "name" -- same error.

                        Side note: you may need to wait for the component to be fully loaded before doing that (but take with a grain of salt).

                        Actually, I think you're on to it here. For some reason, the people who wrote this app (I'm just maintaining it) load all the QML files up-front, rather than as-needed. I think the problem is that this is an empty vector when this function is first called...I need to think of how best to handle that.

                        kshegunovK 1 Reply Last reply
                        0
                        • mzimmersM mzimmers

                          @kshegunov said in accessing aggregates (QVector of a struct):

                          @mzimmers said in accessing aggregates (QVector of a struct):

                          TypeError: Cannot read property 'm_name' of undefined

                          Your property is called name, also check the elements you get in that array.

                          Tried with "name" -- same error.

                          Side note: you may need to wait for the component to be fully loaded before doing that (but take with a grain of salt).

                          Actually, I think you're on to it here. For some reason, the people who wrote this app (I'm just maintaining it) load all the QML files up-front, rather than as-needed. I think the problem is that this is an empty vector when this function is first called...I need to think of how best to handle that.

                          kshegunovK Offline
                          kshegunovK Offline
                          kshegunov
                          Moderators
                          wrote on last edited by kshegunov
                          #23

                          @mzimmers said in accessing aggregates (QVector of a struct):

                          Actually, I think you're on to it here. For some reason, the people who wrote this app (I'm just maintaining it) load all the QML files up-front, rather than as-needed. I think the problem is that this is an empty vector when this function is first called...I need to think of how best to handle that.

                          Check that through the console. If you want, you can try to wait for the component by adding[1]:

                          Component.onCompleted: <js code to do w/e>
                          

                          [1]: https://doc.qt.io/qt-5/qml-qtqml-component.html#completed-signal

                          Read and abide by the Qt Code of Conduct

                          1 Reply Last reply
                          0
                          • fcarneyF Offline
                            fcarneyF Offline
                            fcarney
                            wrote on last edited by fcarney
                            #24

                            Okay, I tested it. I cannot get Q_GADGET to work so I used Q_OBJECT:
                            class in main.cpp:

                            using ReagentBottleType = int;
                            class BottleData : public QObject
                            {
                                Q_OBJECT
                            
                                Q_PROPERTY(int volume MEMBER m_volume NOTIFY somethingChanged)
                                Q_PROPERTY(int amountNeeded MEMBER m_amountNeeded NOTIFY somethingChanged)
                                Q_PROPERTY(int position MEMBER m_position NOTIFY somethingChanged)
                                Q_PROPERTY(std::string name MEMBER m_name NOTIFY somethingChanged)
                                Q_PROPERTY(ReagentBottleType bottleType MEMBER m_bottleType NOTIFY somethingChanged)
                            public:
                                BottleData(QObject* parent=nullptr)
                                    : QObject(parent)
                                {
                                    connect(this, &BottleData::somethingChanged, [this](){
                                        qDebug() << "somethingChanged" << m_position << QString::fromStdString(m_name) << m_volume;
                                    });
                                }
                            
                                int m_volume=0;               // amount in bottle (in uL)
                                int m_amountNeeded=0;         // amount needed for synth (in uL)
                                int m_position=0;                  // still figuring this one out
                                std::string m_name="";              // name of the reagent
                                int m_bottleType=0;  // bottle type.
                            
                            signals:
                                void somethingChanged();
                            };
                            

                            setting contextProperty in main.cpp for testing:

                            TestObj testobj;
                            auto context = engine.rootContext();
                            context->setContextProperty("varlisttestobj", &testobj);
                            

                            QML to exercise the object in C++:

                            Column {
                                    anchors.top: listview1.bottom
                                    Repeater {
                                        model: varlisttestobj.varList
                            
                                        Row {
                                            id: bottledelegate
                            
                                            width: 50
                                            spacing: 20
                            
                                            Component.onCompleted: console.log(modelData, modelData.position, modelData.volume)
                            
                                            Timer {
                                                interval: 1000
                                                repeat: true
                                                running: true
                                                onTriggered: {
                                                    modelData.volume += 1
                                                }
                                            }
                            
                                            Text {
                                                text: modelData.position
                                                height: 20
                                            }
                                            Text {
                                                text: modelData.volume
                                                height: 20
                                            }
                                        }
                                    }
                                }
                            

                            QML did not like uint32_t at all. So you will have to find another type that it likes on that page with compatible QML types I linked earlier.

                            C++ is a perfectly valid school of magic.

                            1 Reply Last reply
                            1
                            • fcarneyF Offline
                              fcarneyF Offline
                              fcarney
                              wrote on last edited by
                              #25

                              Oops, I forgot test object in main.cpp:

                              class TestObj : public QObject
                              {
                                  Q_OBJECT
                                  Q_PROPERTY(QVariantList varList READ varList NOTIFY varListChanged)
                                  //Q_PROPERTY(QObjectList objList READ objList NOTIFY objListChanged)
                              
                              public:
                                  TestObj(QObject* parent=nullptr)
                                      : QObject(parent)
                                  {
                                      for(int count=0; count<10; ++count){
                                          auto bottle = new BottleData();
                                          bottle->m_volume = count*10;
                                          bottle->m_position = count;
                                          m_bottleData.append(bottle);
                                      }
                              
                                      emit varListChanged();
                                  }
                              
                                  QVariantList varList(){
                                      QVariantList list;
                                      for(auto bottleData: qAsConst(m_bottleData)){
                                          list.append(QVariant::fromValue(bottleData));
                                      }
                                      return list;
                                  }
                                  /*
                                  QObjectList objList(){
                                      QObjectList list;
                                      for(auto bottleData: qAsConst(m_bottleData)){
                                          list.append(bottleData);
                                      }
                                      return list;
                                  }
                                  */
                              
                              
                              signals:
                                  void varListChanged();
                              
                              private:
                                  QVector<BottleData*> m_bottleData;
                              
                              };
                              

                              C++ is a perfectly valid school of magic.

                              1 Reply Last reply
                              0
                              • fcarneyF Offline
                                fcarneyF Offline
                                fcarney
                                wrote on last edited by
                                #26

                                I didn't expect it to trigger the somethingChanged signal in the BottleData object.

                                C++ is a perfectly valid school of magic.

                                1 Reply Last reply
                                0
                                • fcarneyF Offline
                                  fcarneyF Offline
                                  fcarney
                                  wrote on last edited by
                                  #27

                                  Trying to assign to std::string didnt work either:

                                  modelData.name = "fred"
                                  

                                  error:

                                  Error: Cannot assign QString to an unregistered type
                                  

                                  C++ is a perfectly valid school of magic.

                                  1 Reply Last reply
                                  0
                                  • kshegunovK Offline
                                    kshegunovK Offline
                                    kshegunov
                                    Moderators
                                    wrote on last edited by kshegunov
                                    #28

                                    Okay, so here you go:

                                    types.h

                                    #ifndef TYPES_H
                                    #define TYPES_H
                                    
                                    #include <QObject>
                                    #include <QVector>
                                    #include <QVariant>
                                    #include <QVariantList>
                                    
                                    struct Bottle
                                    {
                                        Q_GADGET
                                    
                                        Q_PROPERTY(QString name MEMBER m_name)
                                        Q_PROPERTY(qreal size MEMBER m_size)
                                    
                                    public:
                                        QString m_name;
                                        qreal m_size;
                                    };
                                    
                                    class DataSource : public QObject
                                    {
                                        Q_OBJECT
                                    
                                    public:
                                        Q_INVOKABLE QVariantList getData();
                                    };
                                    
                                    
                                    #endif // TYPES_H
                                    

                                    main.cpp

                                    #include <QGuiApplication>
                                    #include <QQmlApplicationEngine>
                                    #include <QQmlContext>
                                    
                                    #include "types.h"
                                    
                                    QVariantList DataSource::getData()
                                    {
                                        return {
                                            QVariant::fromValue<Bottle>({ "First bottle", 0.75 }),
                                            QVariant::fromValue<Bottle>({ "Second bottle", 0.70 })
                                        };
                                    }
                                    
                                    int main(int argc, char *argv[])
                                    {
                                        QGuiApplication app(argc, argv);
                                    
                                        QQmlApplicationEngine engine;
                                        engine.addImportPath(QStringLiteral("qrc:/"));
                                        QUrl url(QStringLiteral("qrc:/main.qml"));
                                        QObject::connect(&engine, &QQmlApplicationEngine::objectCreated, &app, [url] (QObject * obj, const QUrl & objUrl) -> void {
                                            if (!obj && url == objUrl)
                                                QCoreApplication::exit(-1);
                                        }, Qt::QueuedConnection);
                                    
                                        DataSource source;
                                        engine.rootContext()->setContextProperty(QStringLiteral("DataSource"), &source);
                                    
                                        qmlRegisterUncreatableType<Bottle>("Example", 1, 0, "Bottle", "");
                                    
                                        engine.load(url);
                                    
                                        return app.exec();
                                    }
                                    

                                    main.qml

                                    import QtQuick 2.15
                                    import QtQuick.Window 2.15
                                    import QtQuick.Controls 2.15
                                    
                                    import Example 1.0
                                    
                                    Window {
                                        id: mainWindow
                                        visible: true
                                        width: 300
                                        height: 200
                                        title: qsTr("Some title")
                                    
                                        Component {
                                            id: template
                                            Text {
                                                text: "defaultText"
                                            }
                                        }
                                    
                                        Column {
                                           Component.onCompleted: DataSource.getData().forEach(function(element) {
                                               template.createObject(this, { text: element.name });
                                           }, this)
                                        }
                                    }
                                    

                                    PS. QML is damn annoying ...

                                    Read and abide by the Qt Code of Conduct

                                    mzimmersM 1 Reply Last reply
                                    1
                                    • kshegunovK kshegunov

                                      Okay, so here you go:

                                      types.h

                                      #ifndef TYPES_H
                                      #define TYPES_H
                                      
                                      #include <QObject>
                                      #include <QVector>
                                      #include <QVariant>
                                      #include <QVariantList>
                                      
                                      struct Bottle
                                      {
                                          Q_GADGET
                                      
                                          Q_PROPERTY(QString name MEMBER m_name)
                                          Q_PROPERTY(qreal size MEMBER m_size)
                                      
                                      public:
                                          QString m_name;
                                          qreal m_size;
                                      };
                                      
                                      class DataSource : public QObject
                                      {
                                          Q_OBJECT
                                      
                                      public:
                                          Q_INVOKABLE QVariantList getData();
                                      };
                                      
                                      
                                      #endif // TYPES_H
                                      

                                      main.cpp

                                      #include <QGuiApplication>
                                      #include <QQmlApplicationEngine>
                                      #include <QQmlContext>
                                      
                                      #include "types.h"
                                      
                                      QVariantList DataSource::getData()
                                      {
                                          return {
                                              QVariant::fromValue<Bottle>({ "First bottle", 0.75 }),
                                              QVariant::fromValue<Bottle>({ "Second bottle", 0.70 })
                                          };
                                      }
                                      
                                      int main(int argc, char *argv[])
                                      {
                                          QGuiApplication app(argc, argv);
                                      
                                          QQmlApplicationEngine engine;
                                          engine.addImportPath(QStringLiteral("qrc:/"));
                                          QUrl url(QStringLiteral("qrc:/main.qml"));
                                          QObject::connect(&engine, &QQmlApplicationEngine::objectCreated, &app, [url] (QObject * obj, const QUrl & objUrl) -> void {
                                              if (!obj && url == objUrl)
                                                  QCoreApplication::exit(-1);
                                          }, Qt::QueuedConnection);
                                      
                                          DataSource source;
                                          engine.rootContext()->setContextProperty(QStringLiteral("DataSource"), &source);
                                      
                                          qmlRegisterUncreatableType<Bottle>("Example", 1, 0, "Bottle", "");
                                      
                                          engine.load(url);
                                      
                                          return app.exec();
                                      }
                                      

                                      main.qml

                                      import QtQuick 2.15
                                      import QtQuick.Window 2.15
                                      import QtQuick.Controls 2.15
                                      
                                      import Example 1.0
                                      
                                      Window {
                                          id: mainWindow
                                          visible: true
                                          width: 300
                                          height: 200
                                          title: qsTr("Some title")
                                      
                                          Component {
                                              id: template
                                              Text {
                                                  text: "defaultText"
                                              }
                                          }
                                      
                                          Column {
                                             Component.onCompleted: DataSource.getData().forEach(function(element) {
                                                 template.createObject(this, { text: element.name });
                                             }, this)
                                          }
                                      }
                                      

                                      PS. QML is damn annoying ...

                                      mzimmersM Offline
                                      mzimmersM Offline
                                      mzimmers
                                      wrote on last edited by
                                      #29

                                      @kshegunov said in accessing aggregates (QVector of a struct):

                                      PS. QML is damn annoying ...

                                      Heh...no argument there, but if I'm reading the tea leaves correctly, it's here to stay.

                                      I understand your C++ code, but I'm still trying to figure out what your QML results in. What exactly is this doing?

                                      Component {
                                              id: template
                                              Text {
                                                  text: "defaultText"
                                              }
                                          }
                                      
                                          Column {
                                             Component.onCompleted: DataSource.getData().forEach(function(element) {
                                                 template.createObject(this, { text: element.name });
                                             }, this)
                                          }
                                      
                                      kshegunovK 1 Reply Last reply
                                      0
                                      • mzimmersM mzimmers

                                        @kshegunov said in accessing aggregates (QVector of a struct):

                                        PS. QML is damn annoying ...

                                        Heh...no argument there, but if I'm reading the tea leaves correctly, it's here to stay.

                                        I understand your C++ code, but I'm still trying to figure out what your QML results in. What exactly is this doing?

                                        Component {
                                                id: template
                                                Text {
                                                    text: "defaultText"
                                                }
                                            }
                                        
                                            Column {
                                               Component.onCompleted: DataSource.getData().forEach(function(element) {
                                                   template.createObject(this, { text: element.name });
                                               }, this)
                                            }
                                        
                                        kshegunovK Offline
                                        kshegunovK Offline
                                        kshegunov
                                        Moderators
                                        wrote on last edited by kshegunov
                                        #30

                                        @mzimmers said in accessing aggregates (QVector of a struct):

                                        I understand your C++ code, but I'm still trying to figure out what your QML results in. What exactly is this doing?

                                        Well, I'm leveraging the fact that the QML engine is a glorified object factory. You know the widgets' basics, so with QtQuick it's the same story, more or less. It goes roughly like this:

                                        1. All visual items are derived from QQuickItem, these include the stuff you see in the QML file definition like Text and Column.
                                        2. Component does not(!) derive from QQuickItem, it is a QObject (or rather QQmlComponent) that's supposed to create your QQuickItems by calling QQmlComponent::createObject and passing it the correct visual parent and maybe a set of property values.
                                        3. When you load a QML file, this is what the engine does - it reads and instantiates the component your file represents, hence it creates all the visual and non-visual items described in said file. It parents everything by the way the items are nested (think of it as a big QObject tree). All the visual items are (re)parented to the root QQuickItem so they get painted correctly.
                                        4. After the object tree's loaded and the objects are instantiated you get the completed signal emitted and propagated through your items (visual and non-visual), so you can do w/e.
                                        5. In the above code you attach to the completed signal, then you call the getData to retrieve the list of structs, then forEach of the elements of the array you execute the anonymous function. The function is a dummy mostly. It just needs to go get the reference to the template component (which isn't a visual item, as mentioned) and call it's createObject to create the Text item contained. The first argument of the method is the visual parent (which is the Column in this case) and the second parameter is the set of properties to pass along, which is just the text value retrieved from the structure.

                                        PS. This code's tested (unlike most of the snippets I provide) so you can directly plug it in your project/app and play with it as you wish.

                                        Read and abide by the Qt Code of Conduct

                                        mzimmersM 1 Reply Last reply
                                        2
                                        • kshegunovK kshegunov

                                          @mzimmers said in accessing aggregates (QVector of a struct):

                                          I understand your C++ code, but I'm still trying to figure out what your QML results in. What exactly is this doing?

                                          Well, I'm leveraging the fact that the QML engine is a glorified object factory. You know the widgets' basics, so with QtQuick it's the same story, more or less. It goes roughly like this:

                                          1. All visual items are derived from QQuickItem, these include the stuff you see in the QML file definition like Text and Column.
                                          2. Component does not(!) derive from QQuickItem, it is a QObject (or rather QQmlComponent) that's supposed to create your QQuickItems by calling QQmlComponent::createObject and passing it the correct visual parent and maybe a set of property values.
                                          3. When you load a QML file, this is what the engine does - it reads and instantiates the component your file represents, hence it creates all the visual and non-visual items described in said file. It parents everything by the way the items are nested (think of it as a big QObject tree). All the visual items are (re)parented to the root QQuickItem so they get painted correctly.
                                          4. After the object tree's loaded and the objects are instantiated you get the completed signal emitted and propagated through your items (visual and non-visual), so you can do w/e.
                                          5. In the above code you attach to the completed signal, then you call the getData to retrieve the list of structs, then forEach of the elements of the array you execute the anonymous function. The function is a dummy mostly. It just needs to go get the reference to the template component (which isn't a visual item, as mentioned) and call it's createObject to create the Text item contained. The first argument of the method is the visual parent (which is the Column in this case) and the second parameter is the set of properties to pass along, which is just the text value retrieved from the structure.

                                          PS. This code's tested (unlike most of the snippets I provide) so you can directly plug it in your project/app and play with it as you wish.

                                          mzimmersM Offline
                                          mzimmersM Offline
                                          mzimmers
                                          wrote on last edited by
                                          #31

                                          @kshegunov OK, I think I understand 1-4. But where is the getData() function explicitly referenced/called? (I think your getData() is the equivalent to my QVariantList BottleList::getBottleListQv().)

                                          I still don't understand how to retrieve the information to use it in my bottle objects.

                                                  Bottle {
                                                      id: bottle1
                                                      cellX: 25
                                                      cellY: 105
                                                      cellHeight: 75
                                                      cellWidth: 75
                                                      bottleScaleFactor: scaleFactor
                                                      cellText: "W7" // how to replace this with something from getData()?
                                                      cellColor: "red"
                                                  }
                                          

                                          Thanks...

                                          ODБOïO kshegunovK 2 Replies Last reply
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