QQuickItem* object. "Expression must have class type" when using

Hodenbrecher

hi,

I'm trying to convert this python code in C++

def setPresetBase( self ):
        object = self.view.rootObject()
        items = object.childItems()
        parameters = []
        for i in items:
            if type(i) == QtQuick.QQuickItem and i.objectName() != "" and i.objectName() != "EditPanel" and i.objectName() != "EditGrid":
                parameters.append( [ i.objectName(), i.x(), i.y(), i.z(), i.width(), i.height(), i.isVisible() ] )
        self._preset_base = Preset( "base", parameters )

i started to write this but i can't use w_object, the visual studio tells me that the expression must have a class type. So I can't call childItems().

void PresetModel::setPresetBase(void)
		{
			QQuickItem* w_object = mp_view->rootObject();
			QList<QQuickItem*> w_items = w_object.childItems();
		}

That's just a pointer so I don't need to allocate any QQuickItem, right ? What's wrong ?

J.Hilk

@Hodenbrecher
I'm not sure, what mp_view is, so I can't say for sure, but my guess is rootObject() returns and actual QObject pointer not a QQuickItem pointer.
So you'll have to cast it:

{
			QQuickItem* w_object = qObject_cast<QQuickItem*> (mp_view->rootObject());
			QList<QQuickItem*> w_items = w_object.childItems();
		}

Nifiro

It's a pointer. Use -> instead of .

w_object->childItems()

Hodenbrecher

@J.Hilk
thanks for your answer.

mp_view is a QQuickView*

QQuickView * mp_view;
PresetModel::PresetModel(QQuickView * aip_view, QObject * aip_parent/*=nullptr by default*/):mp_view(aip_view)
{
}

The documentation says that rootObject returns a QQuickitem* : https://doc.qt.io/qt-5/qquickview.html#rootObject

However I tried the qobject_cast and the IDE says
no instance of overloaded function "qobject_cast" matches the argument list
arguments are: (QQuickItem*)

@Nifiro
i tried, of course. But because it did not work I tried with the "."
Anyway, visual studio underlines the error before any compilation. Just by checking the code.

The error is weird as I can compile

QQuickItem* w_object = mp_view->rootObject();
   		if (w_object == nullptr);

But if I try to access to it's attribute... NO !!!

[edit]
I can't tell if the pointer is null, there's another error probably not linked.

int argc = 0; char** argv=nullptr;
	QGuiApplication(argc, argv);

	QQuickView* view = new QQuickView();//in console : "QPixmap: Must construct a QGuiApplication before a QPixmap

	view->setResizeMode(QQuickView::SizeRootObjectToView);
	QQmlContext *ctxt = view->rootContext();
	view->setSource(QString(QML_GENERIC_VIEW_PATH));
	QQuickItem* w_object = view->rootObject();

	if (w_object == nullptr)printf("\nthe pointer is null\n");
	else printf("\nthe pointer is not null\n");
	QList<QQuickItem*> w_items = w_object->childItems();//got the same error here. w_object underlined

J.Hilk

@Hodenbrecher

possible stupid question, but did you #include <QQuickItem> ?

Hodenbrecher

@J.Hilk this is never a stupid question haha

problem solved. thank you very much

I didn't know that the program could know the type QQuickItem and compile a QQuickItem* object while missing the include...

J.Hilk

@Hodenbrecher
one of the quirks of c++

QQuickItem is a forward-declared class
https://en.cppreference.com/w/cpp/language/class#Forward_declaration