Signal Slot connection from different classes



  • Hello people,

    I have two different classes, lets say Class_A and Class_B, where:

    @
    Class_A::Class_A( Class_B &ref, QWidget *a_parent )
    : QDockWidget( "DOCKW", a_parent )
    , ref2ClassB( ref )
    {
    connect( ref2ClassB, SIGNAL(trigger_Do_Some(int, int)), this, SLOT( slot_Do_Some(int, int)) );
    }

    void Class_A::slot_Do_Some(int value1, int value2)
    {
    //.. do work
    }
    //EOF
    @

    and in its header:
    @
    class Class_A
    : public QDockWidget
    , public Ui_DockWidget
    {
    Q_OBJECT
    public:
    Class_A( Class_B &ref2b, QWidget *parent);

    private slots:
    

    void slot_Do_Some(int, int);

    private:
        Class_B &ref2ClassB; ///< Reference to Class_B.
    

    };
    #endif
    //EOF
    @

    As you can see in Class_B:
    @
    class Class_B
    {
    private:
    void aMethod();

    signals:
    void trigger_Do_Some(int, int);
    };
    #endif
    @

    and its source:
    @
    void Class_B::aMethod( void )
    {
    // blabla
    int t = 32;
    int r = 45;
    emit trigger_Do_Some(t, r);
    }
    // EOF
    @
    Class_A is parent and contains a reference to Class_B. My intention is following: When I call Class_B::aMethod() SIGNAL trigger_Do_Some(int, int) is being emitted.
    And in the parent class this signal is connected to its slot. Unfortunately I get a error:
    @
    error C2664: 'bool QObject::connect(const QObject *,const char *,const QObject *,const char *,Qt::ConnectionType)' : cannot convert parameter 1 from 'Class_B' to 'const QObject *'
    @

    Does anybody have a solution for me? Thanks in advise

    Huck


  • Moderators

    Q_OBJECT is missing in Class_B . That should help.



  • You need that Class_B inherited QObject or derived from it, then add macro Q_OBJECT:
    @class Class_B: public QObject
    {
    Q_OBJECT
    private:
    void aMethod();

    signals:
    void trigger_Do_Some(int, int);
    };@
    and in "connect":http://doc.qt.nokia.com/latest/qobject.html#connect use pointers.



  • You need Q_OBJECT declaration in class B.. isnt it ?



  • Not really, I just added Q_OBJECT, but I have the same error.
    class Class_B : public QThread, public QObject, also the same error.

    Then I added via Singleton:
    @
    const Class_B * pCB = ref2ClassB.GetInstance();
    connect( pCB, SIGNAL(trigger_Do_Some(int, int)), this, SLOT( slot_Do_Some(int, int)) );
    @

    Now I can compile, but therefore LNK2001 and LNK2019 link errors.



  • Ok, LNK2001 gone, when I removed Q_OBJECT from Class_B. I only let Class_B : public QThread, public QObject



  • Just use
    class Class_B : public QThread

    QThread is already inherited from QObject.
    Does it work ?



  • QThread inherits from QObject, so class Class_B : public QThread -,public QObject-



  • Ok, removed.

    @
    const Class_B * pCB = ref2ClassB.GetInstance();
    /// error C2594: 'argument' : ambiguous conversions from 'const Class_B *' to 'const QObject *'
    connect( pCB, SIGNAL(trigger_Do_Some(int, int)), this, SLOT( slot_Do_Some(int, int)) );
    /// error C2664: 'bool QObject::connect(const QObject *,const char *,const QObject *,const char *,Qt::ConnectionType)' : cannot convert parameter 1 from 'Class_B' to 'const QObject *'
    1> No user-defined-conversion operator available that can perform this conversion, or the operator cannot be called
    connect( ref2ClassB, SIGNAL(trigger_Do_Some(int, int)), this, SLOT( slot_Do_Some(int, int)) );
    @



  • [quote]
    All classes that contain signals or slots must mention Q_OBJECT at the top of their declaration. They must also derive (directly or indirectly) from QObject.
    [/quote] from "here":http://doc.qt.nokia.com/4.7/signalsandslots.html

    const Class_B * pCB = ref2ClassB.GetInstance();
    // here the Class_B must inherit from QOBject
    connect( pCB, SIGNAL(trigger_Do_Some(int, int)), this, SLOT( slot_Do_Some(int, int)) );

    // here you need the pointer
    connect( &ref2ClassB, SIGNAL(trigger_Do_Some(int, int)), this, SLOT( slot_Do_Some(int, int)) );



  • [quote author="rokemoon" date="1313050079"]
    // here you need the pointer
    connect( &ref2ClassB, SIGNAL(trigger_Do_Some(int, int)), this, SLOT( slot_Do_Some(int, int)) );
    [/quote]

    This way I get an error C2594: 'argument' : ambiguous conversions from 'Class_B *' to 'const QObject *'



  • Class_B must inherite QObject (directly or indirectly), can you give us latest code of your Class_B?



  • Latest Class_B:
    @
    #include <QtCore/QThread>

    template class SWITCHEXPORT QMap< int, QString >;

    class Class_A;
    class QModelIndex;

    class SWITCHEXPORT Class_B : public QThread {
    Q_OBJECT

    public:
    /// @brief Constructor
    Class_B( void );

    void aMethod();

    signal:
    void trigger_Do_Some(int, int);

    private:
    QMap< int, QString > categoryNameByID;
    }
    @



  • Can you tell us why you use QThread? Can you try inherite from QObject and tell us about result?



  • There is a @QThread::start();@ in the source .cpp .

    So when I inherit from both @clas.s Class_B : public QThread, public QObject@ and I am able to compile it.

    But now I have linking errors:
    @
    3>Linking...
    3> Creating library C:\MyProject\Debug\MyProject.lib and object C:\MyProject\Debug\MyProject.exp
    3>Class_B.obj : error LNK2001: unresolved external symbol "public: static struct QMetaObject const Class_B::staticMetaObject" (?staticMetaObject@Class_B@@2UQMetaObject@@B)
    3>Class_A.obj : error LNK2001: unresolved external symbol "public: static struct QMetaObject const Class_B::staticMetaObject" (?staticMetaObject@Class_B@@2UQMetaObject@@B)
    3>Class_3.obj : error LNK2001: unresolved external symbol "public: static struct QMetaObject const Class_B::staticMetaObject" (?staticMetaObject@Class_B@@2UQMetaObject@@B)
    3>Class_B.obj : error LNK2001: unresolved external symbol "public: virtual struct QMetaObject const * __thiscall Class_B::metaObject(void)const " (?metaObject@Class_B@@UBEPBUQMetaObject@@XZ)
    3>Class_B.obj : error LNK2001: unresolved external symbol "public: virtual void * __thiscall Class_B::qt_metacast(char const *)" (?qt_metacast@Class_B@@UAEPAXPBD@Z)
    3>Class_B.obj : error LNK2001: unresolved external symbol "public: virtual int __thiscall Class_B::qt_metacall(enum QMetaObject::Call,int,void * *)" (?qt_metacall@Class_B@@UAEHW4Call@QMetaObject@@HPAPAX@Z)
    3>Class_B.obj : error LNK2019: unresolved external symbol "protected: void __thiscall Class_B::trigger_Do_Some(long,long)" (?trigger_Do_Some@Class_B@@IAEXJJ@Z) referenced in function "public: virtual void __thiscall Class_B::HandleMessage(void * const)" (?HandleMessage@Class_B@@UAEXQAX@Z)
    3>C:\MyProject\Debug\MyProject.dll : fatal error LNK1120: 5 unresolved externals
    @



  • When you have added Q_OBJECT to Class_B.h recently, then assure yourself that moc_ClassB.cxx has been generated as well.
    If that is the case, this moc-file should be listed in the .pro or .vcpro file as Source
    e.g.:
    @
    <Files>
    <Filter Name="Source Files">
    <File RelativePath="C:\path\moc_Class_B.cxx">
    </File>
    <!-- ....etc...-->
    @



  • I added these tags to the vcpro file, now I can compile and run my application.

    However, now I have a
    @
    warning C4584: 'Class_B' : base-class 'QObject' is already a base-class of 'OtherClass'
    @

    I dont like warnings :(



  • Multiple inheritance is NOT supported for QObject based classes. Can you change your code?



  • main.cpp :
    @
    #include <QtGui>
    #include <converter.h>

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

    QGraphicsScene scene(0,0,500,300);
    QGraphicsView view(&scene);
    
    QLabel *l = new QLabel();
    QSlider *s = new QSlider();
    
    l->setText("Move the slider handle");
    s->setOrientation(Qt::Horizontal);
    
    l->setGeometry(100,100,150,50);
    s->setGeometry(100,200,150,50);
    
    Converter *ms = new Converter(s,l);
    
    
    scene.addWidget(l);
    scene.addWidget(s);
    
    view.show();
    return app.exec&#40;&#41;;
    

    }@

    converter.cpp :
    @
    #include "converter.h"

    Converter::Converter(QSlider *s, QLabel *l)
    {
    connect(s,SIGNAL(valueChanged(int)),this,SLOT(Changer(int)));
    connect(this,SIGNAL(Changer(QString)),l,SLOT(setText(QString)));
    }

    void Converter::Changer(int x)
    {
    Changer(QString::number(x));
    }
    @

    converter.h :
    @
    #ifndef CONVERTER_H
    #define CONVERTER_H

    #include <QtGui>

    class Converter : public QObject
    {
    Q_OBJECT

    public:
    Converter(QSlider*,QLabel*);

    protected slots:
    void Changer(int);

    signals:
    void Changer(QString);

    };

    #endif // CONVERTER_H
    @

    [Edit: Please use @ tags around code. I have added them here. -- mlong]



  • Use Q_PROPERTY for passing arguments in Class-B


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