CodePudding user response:

 


1. Create a new Qt project 

File - & gt; New construction or project - & gt; Other projects - & gt; Empty Qt project 

Such as named Qt_Instance_Example 




2. Add a c + + source file 

Such as named main. The CPP 

Add the following code 


[HTML] view plaincopyprint? 
01. # include & lt; QApplication> 
02. # include & lt; Mypainterwidget. H> 
03. 
04. Int main (int arg c, char * * argv) 
05. {
06. QApplication a (arg c, argv); 
7. 
08. MyPainterWidget w (0); 
09. Baron how (); 
10. Return a.e xec (); 
11.} 
# include & lt; QApplication> 
# include & lt; Mypainterwidget. H> 

Int main (int arg c, char * * argv) 
{
QApplication a (arg c, argv); 

MyPainterWidget w (0); 
Baron how (); 
Return a.e xec (); 
} 
Here MyPainterWidget class is a subclass of our own writing QWidget class, used to implement the draw widgets, 


We add this class and write the code below, 

3. Add a c + + class, named MyPainterWidget 

.h files below 

(CPP) view plaincopyprint? 
01. # # ifndef MYPAINTERWIDGET_H 
02. # define MYPAINTERWIDGET_H 
03. 
04. # include & lt; QWidget> 
05. # include & lt; QPoint> 
06. # include 
7. 
08. Using namespace STD. 
09. 
10. 
11.//line 
12. Typedef struct myLine {
13. QPoint startPnt; 
14. QPoint endPnt; 
15.} myLine; 
16. 
17. The class MyPainterWidget: public QWidget 
18. {
19. Public: 
20. MyPainterWidget (QWidget * parent); 
21. ~ MyPainterWidget (); 
22. 
23.//inheritance 
24. The void paintEvent (QPaintEvent * p); 
25. The void mousePressEvent (QMouseEvent * e); 
26. The void mouseMoveEvent (QMouseEvent * e); 
27. The void mouseReleaseEvent (QMouseEvent * e); 
28. 
29. The QPoint startPnt;//start 
30. QPoint endPnt;//the end 
31. Bool isPressed;//whether the mouse press 
32. 
33. Vector34.}; 
35. 
36 # endif//MYPAINTERWIDGET_H 
# # ifndef MYPAINTERWIDGET_H 
# define MYPAINTERWIDGET_H 

# include & lt; QWidget> 
# include & lt; QPoint> 
# include 

using namespace std; 


//line 
Typedef struct myLine {
The QPoint startPnt; 
The QPoint endPnt; 
} myLine; 

The class MyPainterWidget: public QWidget 
{
Public: 
MyPainterWidget (QWidget * parent); 
~ MyPainterWidget (); 

//inheritance 
Void paintEvent (QPaintEvent * p); 
Void mousePressEvent (QMouseEvent * e); 
Void mouseMoveEvent (QMouseEvent * e); 
Void mouseReleaseEvent (QMouseEvent * e); 

The QPoint startPnt;//start 
The QPoint endPnt;//the end 
Bool isPressed;//whether the mouse press 

Vector}; 

# endif//MYPAINTERWIDGET_H 
.cpp file the following 


(CPP) view plaincopyprint? 
01. # include "mypainterwidget. H" 
02. # include & lt; QString> 
03. # include & lt; QMessageBox> 
04. # include & lt; QPainter> 
05. # include & lt; QPen> 
06. # include & lt; QMouseEvent> 
7. 
08. 
09. MyPainterWidget: : MyPainterWidget (QWidget * parent) 
10. : QWidget (parent) {
11. SetMinimumSize (240120); 
12. SetMaximumSize (480240); 
13. This - & gt; SetMouseTracking (true); 
14. This - & gt; IsPressed=false; 
15.} 
16. 
17. MyPainterWidget: : ~ MyPainterWidget () {
18. 
19.} 
20. 
21. The void MyPainterWidget: : paintEvent (QPaintEvent * p) {
22. QPainter painter (this); 
23. The QPen pen;//create a brush 
24. The pen. SetColor (Qt: : darkCyan); 
25. The pen. SetWidth (5); 
26. The painter. SetPen (pen); 
27. 
28. For (int I=0; i29. MyLine * pLine=lines [I]; 
30. Painter. DrawLine (pLine - & gt; StartPnt pLine - & gt; EndPnt); 
31.} 
32.} 
33. 
34. Void MyPainterWidget: : mousePressEvent (QMouseEvent * e) {
35. SetCursor (Qt: : PointingHandCursor); 
36 startPnt=e - & gt; Pos (); 
37. EndPnt=e - & gt; Pos (); 
38. This - & gt; IsPressed=true; 
39.//a QString MSG="(" + QString: : number (e - & gt; (x)) + ", "+ QString: : number (e - & gt; Y ()) + ") "; 
40.//QMessageBox: : warning (this, tr (" warning "), MSG, QMessageBox: : Ok); 
41.} 
42. 
43. The void MyPainterWidget: : mouseMoveEvent (QMouseEvent * e) {
44. The if (this - & gt; IsPressed) {
45. EndPnt=e - & gt; Pos (); 
46. 
47. MyLine * line=new myLine;//put the new line into the vector 
48. The line - & gt; StartPnt=startPnt; 
49. The line - & gt; EndPnt=endPnt; 
50. This - & gt; Lines. The push_back (line); 
51. 
52. The update ();//repainter, call paintEvent 
53. StartPnt=endPnt; 
54.} 
55.} 
56. 
57. The void MyPainterWidget: : mouseReleaseEvent (QMouseEvent * e) {
58. SetCursor (Qt: : ArrowCursor); 
59. This - & gt; nullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnullnull