Hi everyone,

I have a question in "c++ gui programming with qt 4" chapter 5-4 example(Plotter):

[plotter.h]
Qt Code: 
  1. #ifndef PLOTTER_H
  2. #define PLOTTER_H
  3.  
  4. //QMap store (key, value) pairs and provides fast lookup of the value associated with a key.
  5. #include <QMap>
  6. #include <QPixmap>
  7. #include <QVector>
  8. #include <QWidget>
  9.  
  11. class PlotSettings;
  12.  
  13. class Plotter : public QWidget {
  14. 	Q_OBJECT
  15.  
  16. public:
  17. 	Plotter(QWidget *parent = 0);
  18.  
  19. 	void setPlotSettings(const PlotSettings &settings);
  20. 	void setCurveData(int id, const QVector<QPointF> &data);
  21. 	void clearCurve(int id);
  22. 	QSize minimumSizeHint() const;
  23. 	QSize sizeHint() const;
  24.  
  25. protected:
  26. 	void paintEvent(QPaintEvent *event);
  27. 	void resizeEvent(QResizeEvent *event);
  28. 	void mousePressEvent(QMouseEvent *event);
  29. 	void mouseMoveEvent(QMouseEvent *event);
  30. 	void mouseReleaseEvent(QMouseEvent *event);
  31. 	void KeyPressEvent(QkeyEvent *event);
  32. 	void wheelEvent(QWheelEvent *event);
  33.  
  34. private:
  35. 	void updateRubberBandRegion();
  36. 	void refreshPixmap();
  37. 	void drawGrid(QPainter *painter);
  38. 	void drawCurves(QPainter *painter);
  39.  
  40. 	enum { Margin = 50 };
  41.  
  42. 	QToolButton *zoomInButton;
  43. 	QToolButton *zoomOutButton;
  44. 	QMap<int, QVector<QPointF> > curveMap;
  45. 	QVector<PlotSettings> zoomStack;
  46. 	int curZoom;
  47. 	bool rubberBandIsShown;
  48. 	QRect rubberBandRect;
  49. 	QPixmap pixmap;
  50. };
  51.  
  52. class PlotSettings {
  53.  
  54. public:
  55. 	PlotSettings();
  56.  
  57. 	void scroll(int dx, int dy);
  58. 	void adjust();
  59. 	double spanX() const {
  60. 		return maxX - minX;
  61. 	}
  62. 	double spanY() const {
  63. 		return maxY - minY;
  64. 	}
  65.  
  66. 	double maxX;
  67. 	double minX;
  68. 	int numXTicks;
  69. 	double maxY;
  70. 	double minY;
  71. 	int numYTicks;
  72.  
  73. private:
  74. 	static void adjustAxis(double &min, double &max, int &numTicks);
  75. };
  76.  
  77. #endif
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[plotter.cpp]
Qt Code: 
  1. #include <QtGui>
  2. #include <cmath>
  3.  
  4. #include "plotter.h"
  5.  
  6. Plotter::Plotter(QWidget *parent) : QWidget(parent) {
  7. 	setBackgroundRole(QPalette::Dark); 
  8. 	setAutoFillBackground(true);
  9. 	setSizePolicy(QSizePolicy::Expanding, QSizePolicy::Expanding);
  10. 	setFocusPolicy(Qt::StrongFocus);
  11. 	rubberBandIsShown = false;
  12.  
  13. 	zoomInButton = new QToolButton(this);
  14. 	zoomInButton->setIcon(QIcon(":/images/zoomIn.png"));
  15. 	zoomInButton->adjustSize();
  16. 	connect(zoomInButton, SIGNAL(clicked()), this, SLOT(zoomIn());
  17.  
  18. 	zoomOutButton = new QToolButton(this);
  19. 	zoomOutButton->setIcon(QIcon(":/images/zoomOut.png"));
  20. 	zoomOutButton->adjustSize();
  21. 	connect(zoomOutButton, SIGNAL(clicked), this, SLOT(zoomOut));
  22.  
  23. 	setPlotSettings(PlotSettings());
  24. }
  25.  
  26.   ......
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and i have question in plotter.cpp,
i never include QToolButton class,
why i can use its constructor and function.

Can someone tell me how to solve the problem?
thanks !