XYZ tracker for QwtPlotSpectrogram

Hi,
I am trying to display the x,y coordinates and the z value under the mouse for a QwtSpectrogram. I have a made simple class derived from QwtPlotPicker to do this, I tried to copy the way QwtPlotPicker derives from QwtPicker, however I have failed, it will not link properly! It must be some simple C++ ism that I don't understand, I am hoping someone can point out my error, or point me to an existing class that already does this!?!

Thank you.
Eric

The compiler warns me about:
qwtspectrogrampicker.cpp:5: warning: 'QwtSpectrogramPicker::QwtSpectrogramPicker(QwtPlo tCanvas*)' redeclared without dllimport attribute: previous dllimport ignored
qwtspectrogrampicker.cpp:10: warning: 'virtual QwtSpectrogramPicker::~QwtSpectrogramPicker()' redeclared without dllimport attribute: previous dllimport ignored
qwtspectrogrampicker.cpp:14: warning: 'virtual QwtText QwtSpectrogramPicker::trackerText(const QPoint&) const' redeclared without dllimport attribute: previous dllimport ignored
qwtspectrogrampicker.cpp:19: warning: 'virtual QwtText QwtSpectrogramPicker::trackerTextF(const QPointF&) const' redeclared without dllimport attribute after being referenced with dll linkage

The linker complains:
./debug\qwtspectrogrampicker.o: In function `QwtSpectrogramPicker':
C:\Data\Proj\Bellatrix/qwtspectrogrampicker.cpp:6: undefined reference to `_imp___ZTV20QwtSpectrogramPicker'
C:\Data\Proj\Bellatrix/qwtspectrogrampicker.cpp:6: undefined reference to `_imp___ZTV20QwtSpectrogramPicker'
C:\Data\Proj\Bellatrix/qwtspectrogrampicker.cpp:6: undefined reference to `_imp___ZTV20QwtSpectrogramPicker'
C:\Data\Proj\Bellatrix/qwtspectrogrampicker.cpp:6: undefined reference to `_imp___ZTV20QwtSpectrogramPicker'

./debug\qwtspectrogrampicker.o: In function `~QwtSpectrogramPicker':
C:\Data\Proj\Bellatrix/qwtspectrogrampicker.cpp:10: undefined reference to `_imp___ZTV20QwtSpectrogramPicker'

./debug\qwtspectrogrampicker.o:C:\Data\Proj\Bellatri x/qwtspectrogrampicker.cpp:10: more undefined references to `_imp___ZTV20QwtSpectrogramPicker' follow
./debug\moc_qwtspectrogrampicker.o:C:\Data\Proj\Bell atrix/debug/moc_qwtspectrogrampicker.cpp:51: undefined reference to `_imp___ZN20QwtSpectrogramPicker16staticMetaObject E'
./debug\moc_qwtspectrogrampicker.o: In function `_static_initialization_and_destruction_0':
C:\Data\Proj\Bellatrix/debug/moc_qwtspectrogrampicker.cpp:43: undefined reference to `_imp___ZN20QwtSpectrogramPicker16staticMetaObject E'

Here is my code:
qwtspectrogrampicker.h

Code:

---

#include "qwt_global.h"
#include "qwt_plot_canvas.h"
#include "qwt_plot_picker.h"
 
class QWT_EXPORT QwtSpectrogramPicker : public QwtPlotPicker
{
    Q_OBJECT
public:
    explicit QwtSpectrogramPicker( QwtPlotCanvas * );
    virtual ~QwtSpectrogramPicker();
 
protected:
    virtual QwtText trackerText( const QPoint & ) const;
    virtual QwtText trackerTextF( const QPointF & ) const;
};

---

and qwtspectrogrampicker.cpp

Code:

---

#include "qwtspectrogrampicker.h"
#include "qwt_plot.h"
#include "qwt_plot_spectrogram.h"
 
QwtSpectrogramPicker::QwtSpectrogramPicker( QwtPlotCanvas *canvas ):
    QwtPlotPicker( canvas )
{
}
 
QwtSpectrogramPicker::~QwtSpectrogramPicker()
{
}
 
QwtText QwtSpectrogramPicker::trackerText( const QPoint &pos ) const
{
    return trackerTextF( invTransform( pos ) );
}
 
QwtText QwtSpectrogramPicker::trackerTextF( const QPointF &pos ) const
{
    QwtPlotItemList list = plot()->itemList(QwtPlotItem::Rtti_PlotSpectrogram);
    if (list.count() == 0)
        return trackerTextF( pos );
    else {
        QwtPlotSpectrogram * sp = static_cast<QwtPlotSpectrogram *> (list.at(0));
        double z = sp->data()->value(pos.x(), pos.y());
 
        QString text;
        text.sprintf( "%.4f, %.4f, %.4f", pos.x(), pos.y(), z );
        return QwtText( text );
    }
}

---

QWT_EXPORT is for classes of the Qwt library only. Don't use it in classes of the application.

Uwe

Thanks Uwe, that did the trick.