In particular, I am implementing a QWizardPage ("MyWizardPage") for a QWizard, and I want to emit a signal ("sigLog") from my override of the QWizardPage::nextId virtual method.
Like so:
class MyWizardPage
: public QWizardPage
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Q_OBJECT
public:
MyWizardPage();
virtual int nextId() const;
Q_SIGNALS:
void sigLog(QString text);
};
int MyWizardPage::nextId() const
{
Q_EMIT sigLog("Something interesting happened");
}
But when I try this, I get the following compile error on the Q_EMIT line:
Error 1 error C2662: 'MyWizardPage::sigLog' : cannot convert 'this' pointer from 'const MyWizardPage' to 'MyWizardPage &'
It is possible to emit a signal from a const method by adding "const" to the signal declaration, like so:
void sigLog(QString text) const;
I tested this and it does compile and run, even though you don't actually implement the signal as a normal method yourself (i.e. Qt is okay with it).
You may try to create another class , declare it as friend for your wizard page and add to wizard as a mutable member. after that you may emit it's signal instead of wizard's.
class ConstEmitter: public QObject
{
Q_OBJECT
...
friend class MyWizardPage;
Q_SIGNALS:
void sigLog(QString text);
};
class MyWizardPage
: public QWizardPage
{
Q_OBJECT
public:
MyWizardPage();
protected:
mutable CostEmitter m_emitter;
Q_SIGNALS:
void sigLog(QString text);
};
int MyWizardPage::nextId() const
{
Q_EMIT m_emitter.sigLog("Something interesting happened");
}
MyWizardPage::MyWizardPage()
{
connect(&m_emitter,SIGNAL(sigLog(QString)),this,SIGNAL(sigLog(QString)));
}
or you may just use
int MyWizardPage::nextId() const
{
Q_EMIT const_cast<MyWizardPage*>(this)->sigLog("Something interesting happened");
}
that is not recommended way, because const_cast is a hack, but it's much shorter :)
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