Sub-classing QCompleter, virtual slot in my sub-class not being called

I am sub-classing QCompleter to give it some special functionality. I want activated() to be fired when there is only one completion in the model with the given prefix, but that's not where I'm having a problem.

I have created a virtual setCompleterPrefix() in my sub-class but the compiler doesn't seem to notice it. Instead the base QCompleter::setCompletionPrefix() is called when the user enters a prefix. Am I doing something wrong?

Here is my class:

#ifndef INSTANTCOMPLETER_H
#define INSTANTCOMPLETER_H

#include <QCompleter>

namespace Reliant
{
class InstantCompleter : public QCompleter
{
    Q_OBJECT
public:
    explicit Ins开发者_运维百科tantCompleter(QObject* parent = 0);

private:

signals:

public slots:
    virtual void setCompletionPrefix(const QString &prefix);

};
}

#endif // INSTANTCOMPLETER_H

Definition:

#include "instantcompleter.h"
using Reliant::InstantCompleter;

InstantCompleter::InstantCompleter(QObject* parent) :
    QCompleter(parent)
{
}

void InstantCompleter::setCompletionPrefix(const QString &prefix)
{
    int completionCount = this->completionCount();
    if(completionCount == 1 && setCurrentRow(0))
        emit activated(currentCompletion());
    else
        QCompleter::setCompletionPrefix(prefix);
}

---

You can use the model returned by QCompleter::completionModel() and its signals to track the completion count:

InstantCompleter::InstantCompleter(QObject* parent) :
    QCompleter(parent)
{
    connect(completionModel(), SIGNAL(layoutChanged()), SLOT(completionModelChanged()));
}

// declared in the "private slots:" section
void InstantCompleter::completionModelChanged()
{
    if (completionCount() == 1 && setCurrentRow(0))
        emit activated(currentCompletion());
}

---

According to this "This method is also a Qt slot with the C++ signature void setCompletionPrefix(const QString&)." from http://www.riverbankcomputing.co.uk/static/Docs/PyQt4/html/qcompleter.html#setCompletionPrefix that function isn't virtual and thus can't be overriden. I suspect that there's an alternate interface to override that capability though.

---

In order to override a method in C++, the base class must define it as virtual. Adding virtual to the method in your subclass does not change this behaviour.

Likewise, there is no way of overriding that method (unless you have a commercial license and change the Qt Framework for your needs which I wouldn't recommend) and you have to think of another way.