objectName property doesn't work as expected in C++ defined QML classes

[nuliknol]

I have a custom QML type which I register like this in main.cpp:

qmlRegisterType<Gate>("client_gate",1,0,"Gate");

qmlRegisterType<Gate>("client_gate",1,0,"Gate");

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Then in main.qml I declare it like this:

Gate {
       id: client_gate
       objectName: "oo"
    }

Gate {
       id: client_gate
       objectName: "oo"
    }

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The problem is I can't find it with my C++ code in main.cpp after QML engine is loaded:

QObject *root = engine.rootObjects()[0];
QObject *o;
o=root->findChild<QObject*>("oo");
if (!o) return 1;
Gate *g;
g=(Gate*) o;
g->set_Client(&client);

QObject *root = engine.rootObjects()[0];
QObject *o;
o=root->findChild<QObject*>("oo");
if (!o) return 1;
Gate *g;
g=(Gate*) o;
g->set_Client(&client);

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I know the code works, because I can find objects of standard QML type (like SwipeView for example) but it doesn't work with my own QML (C++) classes , findChild() just returns null. Why is this happening?
Do I have to define "objectName" property in "Gate" c++ class too ? Isn't it supposed that QObject already has "objectName" property ?

Any help will be greately appreciated.
TIA