Exposing a user defined class / structure to qt meta object system and accessing the same in qml

divaindie

Hi all,
i was trying something like this..i had defined my own class in cpp which is as below.

class myclass{
public :
int k;int m;
QString str;
};

and my code has one more class which has a function ' retval' which will return an object of type myclass

class reduntclass : public QObject {
Q_OBJECT
public :
....................
...................
myclass retval() {
...............
..............
return myclass_object;
}//ret val ends here
....................
...................
....................
...................
};//reduntclass class ends here

and i have exposed "reduntclass" object to qml (with the help of context->setContextProperty("reduntclass", &(reduntclassobj));).also iam able to access reduntclass object from qml.problem is whenever i press a key , qml will call retval function as below

onclicked {
...........
var k = reduntclass.retval()
...........
}

but qml is not able identify the returned value ,and it gives the below errro message
Error: Unknown method return type: myclass
how i can solve this? i think qml is not able to identify myclass type,so i guess i need to expose my 'myclass' class to qt meta object system?

sierdzio

QML only understands QObjects. Your myclass should be a QObject, or at the very least a Q_GADGET.

divaindie

if possible please give one example code

divaindie

i tried the below code . in my .hpp file i have one structure and one class

struct MyStruct {
    Q_GADGET
    int intval;
    QString str1;
    QString str2;
};

class MyClass:public QObject
    {
        Q_OBJECT
public:
     MyClass(QObject *parent = nullptr){
          qDebug() <<"object created ";
    }
    MyStruct strObj;
    ~MyClass() {
    }
MyStruct strObj;
   Q_INVOKABLE  MyStruct getMyStruct() const
     {
         return strObj;
     }
};

in main.cpp i have below piece of code

MyClass classObj;
    context->setContextProperty("classObj",&classObj);

on qml

onClicked: {
             var k  = classObj.getMyStruct()
}

but still getting below error message,what is wrong with the code?? please help!!!

Error: Unknown method return type: MyStruct

jsulm

This post is deleted!

sierdzio

I'm not sure if Q_GADGET will work (QObject will for sure). Things to try:

return a pointer to your gadget, not a copy
declare pointer to your gadget as Qt meta type, register it with QML

VRonin

You can't have a Q_GADGET and a Q_OBJECT in the same header file, moc is not smart enough to process that.

seyed

1- your struct or simple class must have Q_GADGET as minimum
2- you should declare properties in order to access from qml
2- you must declare your struct/class by Q_DECLARE_METATYPE()
3- you must register it using qRegisterMetaType<>() somewhere before loading qml file by engine such as main.cpp

so you have something like this:

struct MyStruct {
    Q_GADGET
    Q_PROPERTY(QString str1 MEMBER m_str1)
public:
    QString m_str1;
};
Q_DECLARE_METATYPE(MyStruct)

main.cpp

//...
qRegisterMetaType<MyStruct>();
//...
engine.load(url);
//...

NOTE: be careful, is seems that nested classes/struct not supported by Qt meta

seyed

@VRonin same header is not problem, but it seems that nested struct/classes with Q_GADGET and Q_OBJECT is not supported.