在QT4中没有这样的信号

Question

I have a signal and a slot that should fit together quite nicely.

class MemberVisitor: public QObject
{
    Q_OBJECT
signals:
    void processMember(Member* member, bool &breakLoop);
public:
    void processList(QList<Member*>* list);
};

along with:

class MemberFinder: public QObject
{
    Q_OBJECT
public slots:
    void processMember(Member* member, bool &breakLoop);
public:
    Member* member();
    MemberFinder(QString memID): m_member(0), m_memID(memID) {};
private:
    Member* m_member;
    QString m_memID;
};

Not exactly complex, right? But I am definitely missing something, because QT keeps giving me the error: "Object::connect: No such signal MemberVisitor::processMember() in OperationsOnMembers.cpp:29"

Here's the code that should be hooking them up:

QObject::connect(visitor, SIGNAL(processMember()), finder, SLOT(processMember()));

I've also tried all the reasonable alternatives, like calling the function on finder. But I keep getting the same problem. What am I missing?

Answer 1

The call to connect() should be:

QObject::connect(visitor, SIGNAL(processMember(Member*, bool&)), 
    finder, SLOT(processMember(Member*, bool&)));

..provided that visitor and finder are pointers.

Answer 2

You need to include the parameter types (but not the parameter names) in the QObject::connect() call. eg

QObject::connect(visitor, SIGNAL(processMember(Member*, bool&)), finder, SLOT(processMember(Member*, bool&)));

That also lets you overload signals and slots, so you can emit signals with the same name but different parameters (same as overloading of a function, which is basically what a slot is).

This also lets you connect a signal to a slot that has fewer parameters. If your Member finder had a second slot as such :

class MemberFinder: public QObject
{
    Q_OBJECT
public slots:
    void processMember(Member* member, bool &breakLoop);
    void processMember(Member* member);
public:
    Member* member();
    MemberFinder(QString memID): m_member(0), m_memID(memID) {};
private:
    Member* m_member;
    QString m_memID;
};

You could connect the same signal to the second slot as such :

QObject::connect(visitor, SIGNAL(processMember(Member*, bool&)), finder, SLOT(processMember(Member*)));