Qt interfaces or abstract classes and qobject_cast()
I have a fairly complex set of C++ classes that are re-written from Java. So each class has a single inherited class, and then it also implements one or more abstract classes (or interfaces).
Is it possible to use qobject_cast()
to convert from a class to one of the interfaces? If I derive all interfaces from QObject
, I get an error due to ambiguous QObject
references. If however, I only have the base class inherited from QObject
, I can't use qobject_cast()
because that operates with QObject
s.
I'd like to be able to throw around classes between plugins and DLLs referred to by t开发者_运维技巧heir interfaces.
After some research and reading the qobject_cast documentation, I found this:
qobject_cast() can also be used in conjunction with interfaces; see the Plug & Paint example for details.
Here is the link to the example: Plug & Paint.
After digging up the interfaces header in the example, I found the Q_DECLARE_INTERFACE macro that should let you do what you want.
First, do not inherit QObject
from your interfaces. For every interface you have, use the Q_DECLARE_INTERFACE declaration like this:
class YourInterface
{
public:
virtual void someAbstractMethod() = 0;
};
Q_DECLARE_INTERFACE(YourInterface, "Timothy.YourInterface/1.0")
Then in your class definition, use the Q_INTERFACES macro, like this:
class YourClass: public QObject, public YourInterface, public OtherInterface
{
Q_OBJECT
Q_INTERFACES(YourInterface OtherInterface)
public:
YourClass();
//...
};
After all this trouble, the following code works:
YourClass *c = new YourClass();
YourInterface *i = qobject_cast<YourInterface*>(c);
if (i != NULL)
{
// Yes, c inherits YourInterface
}
精彩评论