C++ signal and custom type variable use in QML

[penguin_chris]

I have created a custom type inheriting from QObject.
I have declared the type with Q_DECLARE_METATYPE() with qmlDeclareType() and also with qRegisterMetaType().

From another object declared as a component in QML I emit a signal which has the type as a parameter now when the signal is handled from the QML I cannot access any of the properties of the type.
In debug output while debugging

Error: Cannot assign [undefined] to QString
is shown whenever I try to access any property of the variable and

Error: <variableName> is not defined
is shown.

my signal is declared as follows:

signals:
    void readTagBCard(const BCard& tagc);

and handled in qml as follows:

onReadTagBCard:{            
            txtFullName.text = tagc.lastName;
        }

the method is lastName is declared as follows:

QString lastName() const {return mlastName;};

How can I access methods on custom type variables in QML?

[akrynski]

Error: Cannot assign [undefined] to QString

I got this error whenever I tried assign something by object and not by object's id.
I.e. I have

 MyComponent{ id: mySomething //with many non visible properties}

and I tried to use it like in this:

Text{id: sometext; text: "I want to see my class property of QString type. Here it is: " + MyComponent.string_property}

It generates an error and property is undefined.
It should be done so:

MyComponent{ id: mySomething} //first initialize instance of class :)
Text{ id: sometext
         text: mySomething.string_property
...
}

Does it helps?
Regards, Andrzej

[penguin_chris]

My problem is a little bit different since I don't have the component declared in QML. What I am trying to do is to use properties of a class instance sent in signal without declaring it in the QML.

[akrynski]

ok, but i think this undefined value can be essential to find what happens. let us ask a question - why it is undefined?
if your type es really registered it can be instanced in any way and here seems it isn't

I am non sure what are you working on, but perhaps this links will help: http://www.google.pl/url?sa=t&source...-QDHjQ&cad=rja
http://www.google.pl/url?sa=t&source...CfroaA&cad=rja

[penguin_chris]

Thanks for the links but I still can not get it to work... While playing around with it I am now getting the following error

Result of expression 'nfcTagBCard.firstName' [undefined] is not a function.

In my class definition the result of the call to firstName method is a QString and it is declared as a slot so it should be visible from the QML.

[akrynski]

let us see some piece of code

[danhicksbyron]

Stupid question: Did you use the Q_OBJECT macro in your class's H file?

[penguin_chris]

Stupid question: Did you use the Q_OBJECT macro in your class's H file?

Yes, the macro is there

@akrynski: I will post some code later when I have some time to reopen that project...

[j.martin]

Hello, I've exactly the same problem than penguin_chris. I have created a custom type inheriting from QObject and this type is instanciated and emitted from the c++ part in a queued connection
No problem to receive the signal in a c++ slot ; In this case I'm able to read properties of the custom type. However in QML I receive the signal but when I want to read the custom type's properties it returns "undefined"

Just below the code snippet :

// .h : custom types
class EqtEventList : public QObject
{
Q_OBJECT

Q_PROPERTY(QString name READ name)

//number of events in the list
Q_PROPERTY(int eventscount READ eventscount)

//list property containing file names as QString
Q_PROPERTY(QDeclarativeListProperty<EqtEvent> events READ events CONSTANT )


public:

EqtEventList();

EqtEventList(const EqtEventList &eqtEventList);

~EqtEventList();

//properties' read functions
QString name() const { return QString("tutu");};
int eventscount() const;
QDeclarativeListProperty<EqtEvent> events();

QList<QSharedPointer<EqtEvent>> m_eqtEventList;
};

Q_DECLARE_METATYPE(EqtEvent) // EqtEvent class definition is not included in the code snippet, but it is a class which inherits from QObject, like EqtEventList
Q_DECLARE_METATYPE(EqtEventList)

------------------------------------------------

// main.cpp :
qmlRegisterType<EqtEvent>("Events",1,0,"EqtEvent");
qmlRegisterType<EqtEventList>("Events", 1, 0, "EqtEventList");

qRegisterMetaType<EqtEvent>("EqtEvent");
qRegisterMetaType<EqtEventList>("EqtEventList");

------------------------------------------------

// interface.h : abstract class, implementation of virtual methods are done in derived class, (signals are emitted in CEqtProxySoap)
class IEqtProxy : public QObject
{
Q_OBJECT

signals:
void eventsReceived(const EqtEventList eventlist);

....

------------------------------------------------

// eqtProxySoap.cpp
void CEqtProxySoap::notifyEventsReceived(
const EqtEventList eventlist)
{
emit eventsReceived(eventlist);
}

------------------------------------------------

// another.cpp : eventsReceived is not emitted in the GUI thread, so it is a queued connection

EqtEventList eqtEventList;
eqtEventList.m_eqtEventList.append(QSharedPointer<EqtEvent>(new EqtEvent(QString("Test"), QDateTime::currentTime(), QString("1")));

TheEqtInterface.notifyEventsReceived(eqtEventList);

------------------------------------------------

// test.qml

import QtQuick 1.0
import Events 1.0
import "content"

Rectangle {
id: window
width: 600; height: 800
color: "#d9d3b5"

Column {
Text {
id: test
text: "This is a test"

Connections {
target: eqtproxy
onEventsReceived: {
console.log("Received c++ signal : eventlist.name = " + eventlist.name)
}
}
}
}
}

------------------------------------------------

[j.martin]

I you have an idea it would be great ! I'm stucked on that topic for 2 days now...
Thanks