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

Qt Code: 
  1. #include "qwt_global.h"
  2. #include "qwt_plot_canvas.h"
  3. #include "qwt_plot_picker.h"
  4.  
  5. class QWT_EXPORT QwtSpectrogramPicker : public QwtPlotPicker
  6. {
  7.     Q_OBJECT
  8. public:
  9.     explicit QwtSpectrogramPicker( QwtPlotCanvas * );
  10.     virtual ~QwtSpectrogramPicker();
  11.  
  12. protected:
  13.     virtual QwtText trackerText( const QPoint & ) const;
  14.     virtual QwtText trackerTextF( const QPointF & ) const;
  15. };
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and qwtspectrogrampicker.cpp

Qt Code: 
  1. #include "qwtspectrogrampicker.h"
  2. #include "qwt_plot.h"
  3. #include "qwt_plot_spectrogram.h"
  4.  
  5. QwtSpectrogramPicker::QwtSpectrogramPicker( QwtPlotCanvas *canvas ):
  6.     QwtPlotPicker( canvas )
  7. {
  8. }
  9.  
  10. QwtSpectrogramPicker::~QwtSpectrogramPicker()
  11. {
  12. }
  13.  
  14. QwtText QwtSpectrogramPicker::trackerText( const QPoint &pos ) const
  15. {
  16.     return trackerTextF( invTransform( pos ) );
  17. }
  18.  
  19. QwtText QwtSpectrogramPicker::trackerTextF( const QPointF &pos ) const
  20. {
  21.     QwtPlotItemList list = plot()->itemList(QwtPlotItem::Rtti_PlotSpectrogram);
  22.     if (list.count() == 0)
  23.         return trackerTextF( pos );
  24.     else {
  25.         QwtPlotSpectrogram * sp = static_cast<QwtPlotSpectrogram *> (list.at(0));
  26.         double z = sp->data()->value(pos.x(), pos.y());
  27.  
  28.         QString text;
  29.         text.sprintf( "%.4f, %.4f, %.4f", pos.x(), pos.y(), z );
  30.         return QwtText( text );
  31.     }
  32. }
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