[Qt-interest] problem with signal/slot

[Atlant Schmidt]

All:

> Are you sure the moc compiler is running for you file.

  Not just that, but are you sure you're then *USING* the output
  of the moc compiler by passing the produced foo_moc.cpp into
  your main cpp compilation?

  If all that is fine, then the usual problem is a mismatch of signatures
  between the slot declaration and the slot usage in the connect()
  statement. You show them as both having identical (void) signatures,
  but perhaps you simplified that for the e-mail?

                                     Atlant


________________________________
From: qt-interest-bounces at trolltech.com [mailto:qt-interest-bounces at trolltech.com] On Behalf Of Brian McKinnon
Sent: Wednesday, December 08, 2010 12:43
To: qt-interest
Subject: Re: [Qt-interest] problem with signal/slot

Are you sure the moc compiler is running for you file.  Check the info in:




 const QMetaObject* metaObject = obj->metaObject();



 QStringList methods;

 methods << metaObject->className();





 for(int i = metaObject->methodOffset(); i < metaObject->methodCount(); ++i)

     methods << QString::fromLatin1(metaObject->method(i).signature());

On Wed, Dec 8, 2010 at 1:20 PM, Mahendra G.R <mahendra at mahendragr.com<mailto:mahendra at mahendragr.com>> wrote:

Hi,

yes i do put it in a seperate cpp file, just to make it look shorter in the mail i did that :), but still no use, it says method is not found. any other reasons?, thanks for your reply.

On Wed, Dec 8, 2010 at 6:08 PM, Xiaolei Shang <xiaolei.shang at cobham.com<mailto:xiaolei.shang at cobham.com>> wrote:

Hi:
Hi guys,

i have a small problem with signal/slot, though i have defined my slot method, i get runtime message saying   Object::connect: No such slot CustomScene::updateAlphaValue()  , i have defined the method updateAlphaValue() in the customScene class

this is my code :

class CustomScene : public QGraphicsScene
{

    Q_OBJECT
    public:
        CustomScene()
        {
              alphaSlider = new QSlider(Qt::Horizontal);
            alphaSlider->setTickInterval(1);
            alphaSlider->setRange(0,255);
            alphaSlider->setMinimumSize(105,20);
            alphaSlider->move(6,222);
            alphaSlider->setToolTip("Opacity");
            connect( alphaSlider, SIGNAL(valueChanged(int)), SLOT(updateAlphaValue()) );
         //some other stuff
     }

public slots :
            void updateAlphaValue();

};
--
http://www.mahendragr.com
If you move the declaration of updateAlphaValue() to the front of the definition of the constructor, the compiler should be able to see the function. Like this:

class CustomScene : public QGraphicsScene
{

    Q_OBJECT
   public slots :
            void updateAlphaValue();

    public:
        CustomScene()
        {
              alphaSlider = new QSlider(Qt::Horizontal);
            alphaSlider->setTickInterval(1);
            alphaSlider->setRange(0,255);
            alphaSlider->setMinimumSize(105,20);
            alphaSlider->move(6,222);
            alphaSlider->setToolTip("Opacity");
            connect( alphaSlider, SIGNAL(valueChanged(int)), SLOT(updateAlphaValue()) );
         //some other stuff
     }
...
};

As you define your constructor in your declaration scope. You have to declare a function before you call it. Otherwise, the compiler won't see it. However, in this case, this is not a good way for defining the class as it contains many line codes. Implicitly, it's a online function. I would recommand to put the definition of the constructor in a .cpp file.

Cheers

Xiaolei





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--
http://www.mahendragr.com

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