[Qt-qml] Custom data type in slot parameter

[michael.brasser at nokia.com]

Hi Robert,

On 22/10/2010, at 4:06 PM, ext Robert Voinea wrote:
> I have a QtDeclarative application and I want to connect a signal in my C++ 
> code to a QML slot.
> 
> The problem is that the signal in the C++ code has a custom data type 
> (ButtonInformation).
> I have registered the custom data type with qRegisterMetaType,
> Q_DECLARE_METATYPE (so that it can be used with signals/slots) and with 
> qmlRegisterType. 
> 
> If I set the parameter's type to QVariant, the slot gets called but I cannot 
> see any properties of the parameter.

Functions added to an object in QML will have parameters of type QVariant, so this is the correct "connect".

> If I set the parameter's type to ButtonInformation then connect says there is 
> no such slot...
> 
> Any hits on how to achieve this?

I think you are probably running into http://bugreports.qt.nokia.com/browse/QTBUG-13047, which should be fixed for 4.7.1 (commit 1bd2eb8ecd6b2377132beaa789c8b3b8a6f544d9). In the meantime, changing

v.setValue(b);

to

v.setValue(qobject_cast<QObject*>(b));

might get things working (though I haven't tested to confirm).

Regards,
Michael

> Code follows:
> 
> /** Button Information */
> class ButtonInformation;
> Q_DECLARE_METATYPE(ButtonInformation);
> 
> class ButtonInformation : public QObject
> {
> 	Q_OBJECT
> public:
> 	ButtonInformation(QObject* parent = 0);
> 	ButtonInformation(const ButtonInformation& b);
> 	virtual ~ButtonInformation();
> 
> 	Q_PROPERTY(QString text READ text WRITE setText);
> 	QString text() const;
> 	void setText(const QString& s);
> private:
> 	QString m_text;
> };
> 
> /** MainView.h */
> class MainView : public QDeclarativeView
> {
> 	Q_OBJECT
> public:
> 	explicit MainView(QWidget* parent = 0);
> 	virtual ~MainView();
> 	void doSomething();
> signals:
> 	// void buttonAdd(ButtonInformation b);
> 	void buttonAdd(QVariant b);
> };
> 
> /** MainView.cpp */
> void MainView::doSomething()
> {
> 	ButtonInformation b;
> 	b.setText("The Text");
> 	// emit buttonAdd(v);
> 
> 	QVariant v;
> 	v.setValue(b);
> 	emit buttonAdd(v);
> }
> 
> MainView::MainView(QWidget* parent) : QDeclarativeView(parent)
> {
> 	setSource("main.qml");
> 
> 	QObject* obj = rootObject();
> 	if (!obj)
> 		::exit(1);
> 
> 	// connect(this, SIGNAL(buttonAdd(ButtonInformation)), obj, 
> 	// 	SLOT(buttonAdd(ButtonInformation)));
> 	connect(this, SIGNAL(buttonAdd(QVariant)), obj, 
> 		SLOT(buttonAdd(QVariant)));
> 	show();
> }
> 
> /** main.cpp */
> int main(int argc, char** argv)
> {
> 	QApplication app(argc, argv);
> 
> 	qmlRegisterType<ButtonInformation>("btn", 1, 0, "ButtonInformation");
> 	qRegisterMetaType<ButtonInformation>("ButtonInformation");
> 
> 	MainView view;
> 	view.show();
> 	return app.exec();
> }
> 
> /** main.qml */
> import Qt 4.7
> import btn 1.0
> Rectangle
> {
> 	id: main;
> 	property alias text: txt.text;
> 
> 	Text
> 	{
> 		id: txt;
> 		text: "Default text";
> 	}
> 	function buttonAdd(ButtonInformation b)
> 	{
> 		main.text = b.text;
> 	}
> }
> -- 
> Robert Voinea
> IT Specialist
> +4 0740 467 262
> rvoinea (at) gmail [dot] com 
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