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C++ to change QML object properties

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  • 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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    • 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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        • 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)
            {
            }
            @

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            • 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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                                  • p3c0P Offline
                                    p3c0P Offline
                                    p3c0
                                    Moderators
                                    wrote on last edited by
                                    #32

                                    [quote author="Vignes" date="1406045743"]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[/quote]

                                    What is the problem ? You need to elaborate.

                                    bq. onClicked: {if(mouse.button == Qt.RightButton){if(menu.opacity == 0){opacity_1.running = true;}}}

                                    set acceptedButtons: Qt.LeftButton | Qt.RightButton for MouseArea

                                    bq.
                                    QScreen *screen;
                                    qDebug() << "Information for screen:" << screen->name();
                                    .
                                    .
                                    .

                                    @
                                    QScreen *screen = QGuiApplication::primaryScreen();
                                    qDebug() << screen->availableGeometry();
                                    @

                                    157

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                                    • p3c0P Offline
                                      p3c0P Offline
                                      p3c0
                                      Moderators
                                      wrote on last edited by
                                      #33

                                      [quote author="Vignes" date="1406047246"]Could you tell me how to set-up Git in QtCreator Option > Version Control: Configuration, Miscellaneous, Gitk and Repository Browser ?

                                      Thank you[/quote]

                                      May be "this":https://qt-project.org/doc/qtcreator-2.8/creator-version-control.html#using-version-control-systems and a youtube tutorial "here":http://www.youtube.com/watch?v=3Dr05-bFMbw help you. I have never used git from Qt Creator, so can't help you that much on it. I normally do it through command line.

                                      157

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                                      • V Offline
                                        V Offline
                                        Vignes
                                        wrote on last edited by
                                        #34

                                        I tried to add two mouse area function on main window: double clicked and a clicked like below:
                                        @
                                        MouseArea {
                                        id: oneClick
                                        anchors.fill: parent
                                        onClicked: opacity_1.running = true;
                                        }
                                        MouseArea {
                                        id: twoClick
                                        anchors.fill: parent
                                        onDoubleClicked: window1.callCpp()
                                        }
                                        @

                                        • Here only the last muse area function works. So I tried merging two and it works :
                                          @
                                          MouseArea {
                                          id: windowClicks
                                          anchors.fill: parent
                                          onClicked: if(menu.opacity == 0){opacity_1.running = true;}{opacity_1.running = true;}}}
                                          onDoubleClicked: window1.callCpp()
                                          }
                                          @

                                        I wanted a mouse area function for right mouse clicked, for this I tried the bellow:
                                        @
                                        onPressed: {if(mouse.button == Qt.RightButton){if(menu.opacity == 0){opacity_1.running = true;}}}
                                        @

                                        • Here it did not work, but if I change the "Qt.RightButton" to "Qt.LeftButton" it works

                                        Is there any other way to add multiple mouse event to one area?

                                        How do I use the Right click to run a function?

                                        Is it possible to add or modify or remove mouse event in cpp?

                                        Thanks

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                                        • p3c0P Offline
                                          p3c0P Offline
                                          p3c0
                                          Moderators
                                          wrote on last edited by
                                          #35

                                          bq. Is there any other way to add multiple mouse event to one area?

                                          Yes. You just did it by adding onClicked and onDoubleClicked event handler to mousearea

                                          bq. How do I use the Right click to run a function?

                                          As I said earlier you need to set acceptedButtons
                                          @
                                          MouseArea {
                                          id: twoClick
                                          anchors.fill: parent
                                          acceptedButtons: Qt.LeftButton | Qt.RightButton
                                          onClicked: {
                                          if(mouse.button==Qt.RightButton) {
                                          console.log("Right Click")
                                          }
                                          }
                                          }
                                          @

                                          bq. Is it possible to add or modify or remove mouse event in cpp?

                                          You can set enabled property from C++ by finding child as shown earlier.

                                          157

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