Tag Archives: Programming - Page 2

Storing pointer in QVariant

You can store many types of data into QVariant, like int, string, etc. Also you can store pointers, but only pointers to void (void*).
But what happens when you want to set a property of a object to a instance of class, with setProperty, and after that, you want to retrieve that property? QVariant accepts void*, so you can do something like the following, to store it into QVariant:

QVariant v = qVariantFromValue((void *) yourPointerHere);

and then something like this, in order to retrieve it back from QVariant:

yourPointer = (YourClass *) v.value<void *>();

Having this done each time you have to get the property or set the property is a bit tendentious. We can make this more friendly, using templates:

template <class T> class VPtr
    static T* asPtr(QVariant v)
	return  (T *) v.value<void *>();

    static QVariant asQVariant(T* ptr)
	return qVariantFromValue((void *) ptr);

So how do you use this? Assuming you have a class MyClass, and you want to store a pointer to this class as a property of a QWidget, or any QObject, or you want to convert it to QVariant, you can do the following:

MyClass *p;
QVariant v = VPtr<MyClass>::asQVariant(p);

MyClass *p1 = VPtr<MyClass>::asPtr(v);

I think this is more developer friendly than having to write each time those conversion code sequences.