[SOLVED] Compilation error trying to sub-class a Qt QAction class, not sure why

rstewart · 02-08-2011, 09:40 AM

Hi all,

As the title says, I am trying to sub-class a standard Qt QAction class so that I can create an action trigger that sends a QString text message to the event handler. That way I can simply create one event handler for a context menu I need to present and have the event handler figure out which menu item was selected by examining the passed text string. I got the code from an article I read on the net and am including a copy of it.

Code:

class MyAction : public QAction  

{  

  Q_OBJECT  

  public:  

    MyAction(QString someActionInfo)  

      : someActionInfo_(someActionInfo)  

    {  

      connect(this, SIGNAL(triggered()),  

              this, SLOT(onTriggered()));  

    }  

  signals:  

    void triggered(QString someActionInfo);  

  private slots:  

    void onTriggered() {  

      emit triggered(someActionInfo_);  

    }  

  private:  

    QString someActionInfo_;  

};

I am also including a link to the article in case anyone else wants to take a look at it: http://schneide.wordpress.com/tag/qt4/

The error I am receiving is "no matching function call to 'QAction::QAction()'. The error is being generated by the constructor line. I am not sure why the error is being generated, the code looks okay to me. Any help on figuring out what the error is referring to is greatly appreciated.

wshackle · 02-08-2011, 11:34 AM

Try

MyAction(QObject * parent,QString someActionInfo)

: QAction(parent),someActionInfo_(someActionInfo)

{

QAction doesn't have a zero arguments constructor

rstewart · 02-08-2011, 11:45 AM

Yup, that works. For anyone else who may want to try something like this, here is what I finally did:

Code:

class MyAction : public QAction  
{  
  Q_OBJECT  

  public:
    explicit MyAction(QString someActionInfo, QObject *parent)  
      : QAction(someActionInfo, parent)
    {
      someActionInfo_ = someActionInfo;
      connect(this, SIGNAL(triggered()), this, SLOT(onTriggered()));  
    }

  signals:  
    void triggered(QString someActionInfo);

  private slots:  
    void onTriggered() {  
      emit triggered(someActionInfo_);  
    }  

  private:  
    QString someActionInfo_;  
};

You can then set up an event handler to receive a QString. When triggered, the event handler is called and the text originally passed in during the action instantiation is also passed as the QString variable.

Thank you wshackle!