How plot knows when something has been attached to it?

[Spitfire]

Guys,

I'm creating specialized plot object in which I would like to know when an plot item has been attached to it.

I've looked around but I can't find a way to do it.

QwtPlotItem is not an QObject, it doesn't emit any signals.
When it's attached to a plot i calls QwtPlot::attachItem(), but this function doesn't do much nor I can overload it.

Any ideas how plot can know when something has been attached to it?

Cheers!

[Santosh Reddy]

one way is by iterating QwtPlot::itemList()

[d_stranz]

one way is by iterating QwtPlot::itemList()

Yes, that will tell you what is there, but as far as I know there is no way to be notified when something new is added. About the only way is if autoreplot is turned on, then adding something new will trigger a replot. That's not very satisfactory.

[Uwe]

Use YourPlot::attach instead of QwtPlotItem::attach():

class YourPlot: public QwtPlot
{
public:
    ...
    void attach( QwtPlotItem *item, bool on )
    {
        item->attach( this, on );
        emit attached( item, on );
    }
signals:
    void attached( QwtPlotItem *item, bool on );
};

class YourPlot: public QwtPlot
{
public:
    ...
    void attach( QwtPlotItem *item, bool on )
    {
        item->attach( this, on );
        emit attached( item, on );
    }
signals:
    void attached( QwtPlotItem *item, bool on );
};

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Having such a notification makes sense and I will add them for Qwt 6.1.

Uwe

[Spitfire]

Thanks for reply guys.

Uwe: I was thinking about such approach, but then if some regular item will get attached to a plot in usual way - I won't know about it.

I'll wait for 6.1 then if it can't be done now.

Thanks again!