[CLOSED] Qt Q_PROPERTY: how to pass custom C struct in QML

Tycos

Hi to everyone,

this is my problem: I've a C struct (I cannot modify this) and I want pass it to a QML.
For example:

@
typedef struct
{
int a;
int b;
} INT_CUSTOM_STRUCT;

typedef struct
{
char c;
char b;
} CHAR_CUSTOM_STRUCT;

typedef struct
{
INT_CUSTOM_STRUCT num;
CHAR_CUSTOM_STRUCT varChar;
} CUSTOM_C_TYPE;
@

and in the header of my object (c++)
@
class MyCustomClass : public QObject
{
Q_OBJECT
Q_PROPERTY(CUSTOM_C_TYPE myStruct READ getMyStruct CONSTANT)

public:
explicit MyCustomClass(QObject *parent = 0);
CUSTOM_C_TYPE getMyStruct() { return myObj;}

private:
CUSTOM_C_TYPE myObj;
};
@

in main.cpp, I've add this line:
@
int main(int argc, char *argv[])
{
qmlRegisterType<MyCustomClass>("com.example.myClass", 1, 0, "MyCustomClass");
QApplication app(argc, argv);

MyCustomClass *myClass = new MyCustomClass();

QQmlApplicationEngine engine;
engine.load(QUrl(QStringLiteral("qrc:///main.qml")));
engine.rootContext()->setContextProperty("myClass",myClass);


return app.exec&#40;&#41;;

}@

in my Qml:
@
import QtQuick 1.2
import com.example.myClass 1.0

Item {
Component.onCompleted: console.log(myClass.myStruct.num.a);
}
@

It doesn't works...

t3685

Custom properties need to inherit QObject. So you probably need to write a wrapper class for your C struct.

Check the Q_PROPERTY documentation for more information:

http://qt-project.org/doc/qt-5/properties.html#requirements-for-declaring-properties

Tycos

But it's very difficult create a wrapper class.... this is only an example... but I have a very big structure to pass in a qml
I've modify my files in this way:

mycustomclass.h
@
typedef struct
{
int a;
int b;
} INT_CUSTOM_STRUCT;

typedef struct
{
char c;
char b;
} CHAR_CUSTOM_STRUCT;

typedef struct
{
int test;
INT_CUSTOM_STRUCT num;
CHAR_CUSTOM_STRUCT varChar;
} CUSTOM_C_TYPE;

Q_DECLARE_METATYPE(CUSTOM_C_TYPE)

class MyCustomClass : public QObject
{
Q_OBJECT
Q_PROPERTY(CUSTOM_C_TYPE myStruct READ getMyStruct CONSTANT)
public:
explicit MyCustomClass(QObject *parent = 0);
CUSTOM_C_TYPE getMyStruct() { return myObj;}

private:
CUSTOM_C_TYPE myObj;

};
@

mycustomclass.cpp
@
MyCustomClass::MyCustomClass(QObject *parent) :
QObject(parent)
{
myObj.num.a = 10;
myObj.test = 50;
}
@

main.cpp
@
int main(int argc, char *argv[])
{
qmlRegisterType<MyCustomClass>("com.example.myClass", 1, 0, "MyCustomClass");
qRegisterMetaType<CUSTOM_C_TYPE>("CUSTOM_C_TYPE");
QApplication app(argc, argv);

MyCustomClass *myClass = new MyCustomClass();

QQmlApplicationEngine engine;
engine.rootContext()->setContextProperty("myClass",myClass);
engine.load(QUrl(QStringLiteral("qrc:///main.qml")));


return app.exec&#40;&#41;;

}
@

main.qml
@
import QtQuick 2.2
import QtQuick.Controls 1.1
import com.example.myClass 1.0

ApplicationWindow {

Component.onCompleted: console.log(myClass.myStruct)

}
@

output:
@
qml: QVariant(CUSTOM_C_TYPE)
@

if i change my qml file in this way:
@
import QtQuick 2.2
import QtQuick.Controls 1.1
import com.example.myClass 1.0

ApplicationWindow {

Component.onCompleted: console.log(myClass.myStruct.test)

}
@

my new output is:
@
qml: undefined
@

t3685

Please read the documentation some more. The Q_PROPERTY must be a subclass of QObject.
You are using your C-struct as the Q_PROPERTY.

Tycos

thank you for the reply

there isn't an other way to pass this c-native struct to a Qml?

t3685

Not without wrapping it in a QObject-derived class.