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C++ to change QML object properties

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  • V Offline
    V Offline
    Vignes
    wrote on last edited by
    #12

    Hi,
    I have objects window, text and mouse area to text in qml document and I want to implement in c++: when text area is clicked: if the window is not on fullscreen, it should become fullscreen and the text in the text are should change to "Window is Fullscreen" with a animated color chage to "white". Next time it clicked it should come out of fullscreen and chanege the text and color. Also console.log equivalent output of the this event along with screen resolution should be output from c++ (not via qml).

    main.qml :
    @
    import QtQuick 2.2
    import QtQuick.Window 2.1

    Window {
    id: window1
    visible: true
    width: 360
    height: 360
    color: "red"
    title: "MyWindow"

    Text {
        objectName: "myText"
        text: qsTr("Hello World!<br><i>I'm </i><b>not Fullscreen<i> Now</i></b>")
        font.bold: true
        horizontalAlignment: Text.AlignHCenter
        font.family: "Times New Roman"
        font.pointSize: 18
        anchors.centerIn: parent
        color: "steelblue"
    
        MouseArea {
            anchors.fill: parent
        }
    }
    

    }
    @

    main.cpp
    @
    #include <QGuiApplication>
    #include <QQmlApplicationEngine>
    #include <QtQuick/QQuickItem>
    #include <QtQuick/QQuickWindow>

    int main(int argc, char *argv[])
    {
    QGuiApplication app(argc, argv);

    QQmlApplicationEngine engine;
    engine.load(QUrl(QStringLiteral("qrc:///main.qml")));
    

    //here I need function for
    //1 clicke event
    //check fullscreen value
    //2 text changing
    //3 animation
    //4 console.log output of Screen resolution and action
    //5 finaly Window : showMaximized(); or showFullScreen();

    return app.exec();
    

    }
    @

    Could you help me with this please?
    Thank you

    1 Reply Last reply
    0
    • p3c0P Offline
      p3c0P Offline
      p3c0
      Moderators
      wrote on last edited by
      #13

      You can,

      1. Create a QObject based class
      2. Create a SLOT in it
      3. Pass QQuickWindow pointer (which we obtained as shown above) to it
      4. Create a signal in your QML
      5. Do the connections
      6. In the created class cast the QObject pointer to QQuickWindow using qobject_cast
      7. Use this pointer to access/modify the properties of the QML window in the SLOT when the SIGNAL is fired from QML

      157

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      0
      • V Offline
        V Offline
        Vignes
        wrote on last edited by
        #14

        Hi,
        I created QObject: called iobject.h
        @
        #ifndef IOBJECT_H
        #define IOBJECT_H

        #include <QObject>

        class iObject : public QObject
        {
        Q_OBJECT
        Q_PROPERTY(QString name READ name WRITE setName)
        public:
        explicit iObject(QObject *parent = 0);

        QString name() const;
        
            Q_INVOKABLE void nameChang();
        

        signals:
        void nameChanged(int newValue);

        public slots:
        void setName(const QString &name);

        private:
        QString m_name;
        };

        #endif // IOBJECT_H
        @

        iobject.cpp
        @
        #include "iobject.h"

        iObject::iObject(QObject *parent) :
        QObject(parent)
        {
        }
        QString iObject::name() const
        {
        return m_name;
        }
        iObject::setName(const QString &name){
        if(name != m_name)
        m_name = name;
        emit nameChanged(name);
        }
        @

        main.cpp
        @
        #include "iobject.h"
        #include <QGuiApplication>
        #include <QQmlApplicationEngine>

        int main(int argc, char *argv[])
        {
        QGuiApplication app(argc, argv);

        qmlRegisterType<iObject>("myObject", 1, 0, "iObject");
        
        QQmlApplicationEngine engine;
        engine.load(QUrl(QStringLiteral("qrc:///main.qml")));
        
        return app.exec();
        

        }
        @

        main.qml
        @
        import QtQuick 2.2
        import QtQuick.Window 2.1
        import myObject 1.0

        Window {
        visible: true
        width: 360
        height: 360
        title: iObject.name

        MouseArea {
            anchors.fill: parent
            onClicked: {
                Qt.quit();
            }
        }
        
        Text {
            text: qsTr("Hello World!<br><i>I'm </i><b>not Fullscreen<i> Now</i></b>")
            horizontalAlignment: Text.AlignHCenter
            font.family: "Times New Roman"
            font.pointSize: 18
            anchors.centerIn: parent
            color: "steelblue"
        
            MouseArea {
                anchors.fill: parent
            }
        }
        

        }
        @

        At this point, It did not work. erros on main.cpp 'qmlRegisterType'
        what am I doing wrong?

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        0
        • p3c0P Offline
          p3c0P Offline
          p3c0
          Moderators
          wrote on last edited by
          #15

          Just create a the class and pass the QQuickWindow pointer. No need use qmlRegisterType.
          Something like this,
          main.cpp
          @
          QQmlApplicationEngine engine;
          engine.load(QUrl(QStringLiteral("qrc:///main.qml")));
          QQuickWindow *W = (QQuickWindow *)engine.rootObjects().first();
          iObject a(W);
          QObject::connect(engine.rootObjects().first(),SIGNAL(callCpp()),&a,SLOT(onCallCpp()));
          @

          No need of custom properties in the class.
          Remember to cast back QObject back to QQuickWindow in iObject and then you can modify QQuickWindow properties as shown earlier.

          157

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          0
          • V Offline
            V Offline
            Vignes
            wrote on last edited by
            #16

            I'm getting error "main.obj:-1: error: LNK2019: unresolved external symbol "public: __cdecl iObject::iObject(class QObject *)" (??0iObject@@QEAA@PEAVQObject@@@Z) referenced in function main"

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            0
            • p3c0P Offline
              p3c0P Offline
              p3c0
              Moderators
              wrote on last edited by
              #17

              Have you included its corresponding header file (probably iobject.h) in main.cpp ?

              157

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              • V Offline
                V Offline
                Vignes
                wrote on last edited by
                #18

                Yes
                main.cpp
                @
                #include "iobject.h"
                #include <QGuiApplication>
                #include <QQmlApplicationEngine>
                #include <QtQuick/QQuickWindow>

                int main(int argc, char *argv[])
                {
                QGuiApplication app(argc, argv);

                QQmlApplicationEngine engine;
                engine.load(QUrl(QStringLiteral("qrc:///main.qml")));
                
                QQuickWindow *W = (QQuickWindow *)engine.rootObjects().first();
                iObject a(W);
                QObject::connect(engine.rootObjects().first(),SIGNAL(callCpp()),&a,SLOT(onCallCpp()));
                
                return app.exec();
                

                }
                @

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                0
                • p3c0P Offline
                  p3c0P Offline
                  p3c0
                  Moderators
                  wrote on last edited by
                  #19

                  Can you post the new iobject.cpp and .h file ?

                  157

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                  • V Offline
                    V Offline
                    Vignes
                    wrote on last edited by
                    #20

                    iobject.h
                    @
                    #ifndef IOBJECT_H
                    #define IOBJECT_H

                    #include <QObject>

                    class iObject : public QObject
                    {
                    Q_OBJECT
                    public:
                    explicit iObject(QObject *parent = 0);

                    signals:

                    public slots:

                    };

                    #endif // IOBJECT_H
                    @

                    iobject.cpp
                    @
                    #include "iobject.h"

                    iObject::iObject(QObject *parent) :
                    QObject(parent)
                    {
                    }
                    @

                    1 Reply Last reply
                    0
                    • p3c0P Offline
                      p3c0P Offline
                      p3c0
                      Moderators
                      wrote on last edited by
                      #21

                      Everything seems to be fine to me.
                      Try to clean, run qmake and build the project again.
                      Apart from that declare the SLOT onCallCpp in iObject class.

                      157

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                      • V Offline
                        V Offline
                        Vignes
                        wrote on last edited by
                        #22

                        Still same error, the
                        @
                        iObject a(W);
                        @

                        Creates following errors:
                        "main.obj:-1: error: LNK2019: unresolved external symbol "public: _cdecl iObject::iObject(class QObject *)" (??0iObject@@QEAA@PEAVQObject@@@Z) referenced in function main""
                        And
                        "debug\HEVC
                        .exe:-1: error: LNK1120: 1 unresolved externals
                        "
                        I tried cleaning and rebuild it and created a new project and tried it, same error

                        All the code in new project follows:
                        main.qml
                        @
                        import QtQuick 2.2
                        import QtQuick.Window 2.1

                        Window {
                        visible: true
                        width: 360
                        height: 360

                        MouseArea {
                            anchors.fill: parent
                            onClicked: {
                                Qt.quit();
                            }
                        }
                        
                        Text {
                            text: qsTr("Hello World")
                            anchors.centerIn: parent
                        }
                        

                        }
                        @

                        main.cpp
                        @
                        #include <QGuiApplication>
                        #include <QQmlApplicationEngine>
                        #include <QtQuick/QQuickWindow>
                        #include "iobject.h"

                        int main(int argc, char *argv[])
                        {
                        QGuiApplication app(argc, argv);

                        QQmlApplicationEngine engine;
                        engine.load(QUrl(QStringLiteral("qrc:///main.qml")));
                        QQuickWindow *W = (QQuickWindow *)engine.rootObjects().first();
                            iObject a(W);
                            QObject::connect(engine.rootObjects().first(),SIGNAL(callCpp()),&a,SLOT(onCallCpp()));
                        
                        return app.exec();
                        

                        }
                        @

                        iobject.h
                        @
                        #ifndef IOBJECT_H
                        #define IOBJECT_H

                        #include <QObject>

                        class iObject : public QObject
                        {
                        Q_OBJECT
                        public:
                        explicit iObject(QObject *parent = 0);

                        signals:

                        public slots:
                        void onCallCpp();

                        };

                        #endif // IOBJECT_H
                        @

                        iobject.cpp
                        @
                        #include "iobject.h"

                        iObject::iObject(QObject *parent) :
                        QObject(parent)
                        {
                        }
                        @

                        I went though several examples and foud ""Animated Tiles":http://qt-project.org/doc/qt-4.8/animation-animatedtiles.html" example. This one uses different library like QtWidgets, QtCore/qstate.h and main.moc. here not QML. This is an old version qt-4.8 as well.

                        I'm now wondering, that am I using the right QT tool for my project, which uses 4K video playing, editing, analytics tools with the support of OpenGL to be implimented using Cpp.

                        I chose QML, because of built in OpenGL, and Cpp and JS support. Now Qt Widgets, Qt Quick Application, Qt Quick UI and old version, new version are confusion to me.

                        It would be great, If you could please help me with these.

                        Thank you

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                        • p3c0P Offline
                          p3c0P Offline
                          p3c0
                          Moderators
                          wrote on last edited by
                          #23

                          Have the files iobject.cpp and .h included in the project structure from Qt Creator?
                          I have created a small test app based upon the example.
                          Here's the "Link":https://docs.google.com/file/d/0B3rkZH6q1E7ocTdnOFQwNVBDM2c/edit?pli=1
                          Please check if it works.

                          Also Animated Tiles is a completely different example. It doesnot use Qt Quick.
                          Please do not go over to Qt 4.8 or less. It's lot different from Qt 5.3

                          You can refer Qt 5 docs for more information.
                          Following are good links
                          "http://qt-project.org/doc/qt-5/qtqml-index.html":http://qt-project.org/doc/qt-5/qtqml-index.html
                          "http://qt-project.org/doc/qt-5/qtqml-cppintegration-topic.html":http://qt-project.org/doc/qt-5/qtqml-cppintegration-topic.html

                          Let me know if the Sample Application works.

                          157

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                          • V Offline
                            V Offline
                            Vignes
                            wrote on last edited by
                            #24

                            Thanks, your sample works. I got main working after deleting the build folder. Some reason cleaning didn't work, even when I copy and pasted your code.

                            I was thinking like this, creating object and connecting it to QML types:
                            iObject A
                            A.screenSize (connect to Window : visibility)
                            A.textApped (connect to Text : text)
                            A.animantionStart (connect to Animation : start)

                            Then changing it in cpp and then emitting signal or even creating, changing & destroying QML types in cpp. Like JavaScript in HTML application.

                            If you can provide this type of sample works on would be very grateful.

                            *Note: I learn using simple working example rather than reading text with pieces of code, because of my DYSLEXIA.

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                            • p3c0P Offline
                              p3c0P Offline
                              p3c0
                              Moderators
                              wrote on last edited by
                              #25

                              You can also use "QMetaObject::invokeMethod":http://qt-project.org/doc/qt-5/qmetaobject.html#invokeMethod to call a javascript function inside a QML and in that function you can do the operations.
                              For eg.
                              Test.qml
                              @
                              Window {
                              visible: true
                              width: 400
                              height: 400

                              function changeColor() {
                                  rect.color="blue"
                              }
                              
                              Rectangle {
                                  id: rect
                                  anchors.fill: parent
                                  color: "red"
                              }
                              

                              }
                              @

                              and to call it from main.cpp

                              @
                              QMetaObject::invokeMethod(engine.rootObjects().first(), "changeColor");
                              @

                              You can also keep these calls in separate cpp methods of the iObject class.

                              157

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                              • V Offline
                                V Offline
                                Vignes
                                wrote on last edited by
                                #26

                                Say I have following main.qml
                                @
                                Window {
                                visible: true
                                width: 400
                                height: 400

                                Rectangle {
                                id: rect
                                anchors.fill: parent
                                color: "red"
                                
                                    Text {
                                    id: mytext
                                    text: qsTr("<b>Hello World!</b>")
                                    color: "blue"
                                    }
                                    MouseArea {
                                    anchors.fill: parent
                                    onClicked: {
                                        Qt.quit();}
                                    }
                                }
                                

                                }
                                @

                                How do I use this "const char * QMetaObject::className() const" to get Text object name.

                                How do I use "QMetaProperty::write(QObject * object, const QVariant & value) const" to change text value

                                Thank you

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                                • p3c0P Offline
                                  p3c0P Offline
                                  p3c0
                                  Moderators
                                  wrote on last edited by
                                  #27

                                  bq. How do I use this “const char * QMetaObject::className() const” to get Text object name.

                                  As shown earlier you can find the exact Item using findChild and then use "metaObject()":http://qt-project.org/doc/qt-5/qobject.html#metaObject to get it's corresponding metaObject and then use it to get "className()":http://qt-project.org/doc/qt-5/qmetaobject.html#className;

                                  bq. How do I use “QMetaProperty::write(QObject * object, const QVariant & value) const” to change text value

                                  This kind of bit tedious, you have to first findChild then get it's metaObject and then iterate over it to find the exact index of the "property":http://qt-project.org/doc/qt-5/qmetaobject.html#property which you want to set and then change the property for that particular index using "write":http://qt-project.org/doc/qt-5/qmetaproperty.html#write

                                  Alternatively you use more user friendly "setProperty":http://qt-project.org/doc/qt-5/qobject.html#setProperty to directly set it instead of first iterating,finding and then changing.

                                  157

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                                  • V Offline
                                    V Offline
                                    Vignes
                                    wrote on last edited by
                                    #28

                                    how do I fix the following issue
                                    @
                                    MouseArea {
                                    id: oneClick
                                    anchors.fill: parent
                                    onClicked: opacity_1.running = true;
                                    }
                                    MouseArea {
                                    id: twoClick
                                    anchors.fill: parent
                                    onDoubleClicked: window1.callCpp()
                                    }
                                    @

                                    Thank you

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                                    0
                                    • V Offline
                                      V Offline
                                      Vignes
                                      wrote on last edited by
                                      #29

                                      How do I use access mouse right click? I tried the following without success:
                                      @
                                      onClicked: {if(mouse.button == Qt.RightButton){if(menu.opacity == 0){opacity_1.running = true;}}}
                                      @
                                      and
                                      @
                                      onPressed: {if(mouse.button == Qt.RightButton){if(menu.opacity == 0){opacity_1.running = true;}}}
                                      @

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                                      • V Offline
                                        V Offline
                                        Vignes
                                        wrote on last edited by
                                        #30

                                        Could you tell me how to set-up Git in QtCreator Option > Version Control: Configuration, Miscellaneous, Gitk and Repository Browser ?

                                        Thank you

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                                        0
                                        • V Offline
                                          V Offline
                                          Vignes
                                          wrote on last edited by
                                          #31

                                          What am I doing wrong here :
                                          I have included <QScreen>
                                          @
                                          QScreen *screen;
                                          qDebug() << "Information for screen:" << screen->name();
                                          qDebug() << " Available geometry:" << screen->availableGeometry().x() << screen->availableGeometry().y() << screen->availableGeometry().width() << "x" << screen->availableGeometry().height();
                                          qDebug() << " Available size:" << screen->availableSize().width() << "x" << screen->availableSize().height();
                                          qDebug() << " Available virtual geometry:" << screen->availableVirtualGeometry().x() << screen->availableVirtualGeometry().y() << screen->availableVirtualGeometry().width() << "x" << screen->availableVirtualGeometry().height();
                                          qDebug() << " Available virtual size:" << screen->availableVirtualSize().width() << "x" << screen->availableVirtualSize().height();
                                          qDebug() << " Depth:" << screen->depth() << "bits";
                                          qDebug() << " Geometry:" << screen->geometry().x() << screen->geometry().y() << screen->geometry().width() << "x" << screen->geometry().height();
                                          qDebug() << " Logical DPI:" << screen->logicalDotsPerInch();
                                          qDebug() << " Logical DPI X:" << screen->logicalDotsPerInchX();
                                          qDebug() << " Logical DPI Y:" << screen->logicalDotsPerInchY();
                                          @
                                          Help please

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