Can I combine QExplicitlySharedDataPointer and QObject?

kitfox

I'd like to create a shared object using the QExplicitlySharedDataPointer setup, but I also want to use signals and slots to listen for changes to my shared data object.

For example, modifying the example code from the docs a little, is there a way to modify this so that I can connect() a listener to the EmployeeData that will let me know when 'id' or 'name' changes? I don't think I can set that on Employee, since new Employee objects are wrappers around a pointer and are recreated every time I pss them by value:

class EmployeeData : public QSharedData
{
    int _id;
    QString _name;
    
  public:
    EmployeeData() : _id(-1) { }
    EmployeeData(const EmployeeData &other)
        : QSharedData(other), _id(other._id), _name(other._name) { }
    ~EmployeeData() { }

    int id() const { return _id; }
    void setId(int id) 
    {
        if (_id == id)
            return;
        _id = id;
        idChanged();
    }
    
    int name() const { return _name; }
    void setName(QString name) 
    {
        if (_name == name)
            return;
        _name = name;
        nameChanged();
    }
    
  signals:
    void idChanged();
    void nameChanged();
};

class Employee
{
  public:
    Employee() { d = new EmployeeData; }
    Employee(int id, const QString &name) {
        d = new EmployeeData;
        setId(id);
        setName(name);
    }
    Employee(const Employee &other)
          : d (other.d)
    {
    }
    
    int id() const { return d->id(); }
    void setId(int id) { d->setId(id); }

    QString name() const { return d->name(); }
    void setName(const QString &name) { d->setName(name); }


  private:
    QExplicitlySharedDataPointer<EmployeeData> d;
};

mrjj

Hi

Did you try

class EmployeeData : public QObject, public QSharedData
{
Q_OBJECT
....

kitfox

That's not going to work because the EmployeeData object is hidden from the rest of the program by being wrapped in the Employee class. However, I can't turn Employee into a QObject either since it will go out of scope almost as soon as I've finished using it.

jsulm

@kitfox said in Can I combine QExplicitlySharedDataPointer and QObject?:

However, I can't turn Employee into a QObject either since it will go out of scope almost as soon as I've finished using it.

I don't get it: why do you think you can't nake Employee a QObject? How is going out of scope related to base class?