Qt事件学习

一、创建Qt gui应用对应的源码：

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1. //mylineedit.h
2. #ifndef MYLINEEDIT_H
3. #define MYLINEEDIT_H
4. #include <QWidget>
5. #include <QLineEdit>
6. class MyLineEdit : public QLineEdit
7. {
8. public:
9. explicit MyLineEdit(QWidget *parent = 0);
10. protected:
11. void keyPressEvent(QKeyEvent *event);
12. };
13. #endif // MYLINEEDIT_H
14. //mylineedit.cpp
15. #include "mylineedit.h"
16. #include <QLineEdit>
17. #include <QDebug>
18. #include <QKeyEvent>
19. MyLineEdit::MyLineEdit(QWidget *parent):QLineEdit(parent)
20. {
21. }
22. void MyLineEdit::keyPressEvent(QKeyEvent *event)
23. {
24. qDebug() << QObject::tr("MyLineEdit键盘按下事件");
25. }

此时只会出现“MyLineEidt键盘按下事件”。

二、第二次修改

在mylineedit.cpp中keyPressEvent()添加

1. event->ignore(); //忽略该事件

结果：多出现了"Widget键盘按下事件"，并且lineedit无法输入了。

三、第三次修改

在mylineedit.h中添加public函数：

1. bool event(QEvent *event);

然后定义：

1. bool MyLineEdit::event(QEvent *event)
2. {
3. if(event->type() == QEvent::KeyPress)
4. qDebug()<<QObject::tr("MylineEdit的event()函数");
5. return QLineEdit::event(event);
6. }

四、第四次修改

widget.h中public申明：

1. bool eventFilter(QObject *obj,QEvent *event);

widget.cpp构造函数增加代码，并增加事件过滤器函数的定义：

1. lineEdit->installEventFilter(this); //在widget上为lineEdit安装事件过滤器
2. bool Widget::eventFilter(QObject *watched, QEvent *event)
3. {
4. if(watched==lineEdit) {
5. if(event->type()==QEvent::KeyPress)
6. qDebug()<<QObject::tr("Widget的事件过滤器");
7. }
8. return QWidget::eventFilter(watched, event);
9. }

五、最后的源码：
mylineedit:

1. //mylineedit.h
2. #ifndef MYLINEEDIT_H
3. #define MYLINEEDIT_H
4. #include <QWidget>
5. #include <QLineEdit>
6. class MyLineEdit : public QLineEdit
7. {
8. public:
9. explicit MyLineEdit(QWidget *parent = 0);
10. bool event(QEvent *event);
11. protected:
12. void keyPressEvent(QKeyEvent *event);
13. };
14. #endif // MYLINEEDIT_H
15. //mylineedit.cpp
16. #include "mylineedit.h"
17. #include <QLineEdit>
18. #include <QDebug>
19. #include <QKeyEvent>
20. MyLineEdit::MyLineEdit(QWidget *parent):QLineEdit(parent)
21. {
22. }
23. bool MyLineEdit::event(QEvent *event)
24. {
25. if(event->type() == QEvent::KeyPress)
26. qDebug()<<QObject::tr("MylineEdit的event()函数");
27. return QLineEdit::event(event);
28. }
29. void MyLineEdit::keyPressEvent(QKeyEvent *event)
30. {
31. qDebug() << QObject::tr("MyLineEdit键盘按下事件");
32. QLineEdit::keyPressEvent(event);
33. event->ignore();
34. }

midget:

1. //wdiget.h
2. #ifndef WIDGET_H
3. #define WIDGET_H
4. #include <QWidget>
5. class MyLineEdit;
6. namespace Ui {
7. class Widget;
8. }
9. class Widget : public QWidget
10. {
11. Q_OBJECT
12. public:
13. explicit Widget(QWidget *parent = 0);
14. ~Widget();
15. bool eventFilter(QObject *watched, QEvent *event);
16. protected:
17. void keyPressEvent(QKeyEvent *event);
18. private:
19. Ui::Widget *ui;
20. MyLineEdit *lineEdit;
21. };
22. #endif // WIDGET_H
23. //widget.cpp
24. #include "widget.h"
25. #include "ui_widget.h"
26. #include "mylineedit.h"
27. #include <QKeyEvent>
28. #include <QDebug>
29. Widget::Widget(QWidget *parent) :
30. QWidget(parent),
31. ui(new Ui::Widget)
32. {
33. lineEdit = new MyLineEdit(this);
34. lineEdit->move(100, 100);
35. lineEdit->installEventFilter(this); //在widget上为lineEdit安装事件过滤器
36. ui->setupUi(this);
37. }
38. Widget::~Widget()
39. {
40. delete ui;
41. }
42. bool Widget::eventFilter(QObject *watched, QEvent *event)
43. {
44. if(watched==lineEdit) {
45. if(event->type()==QEvent::KeyPress)
46. qDebug()<<QObject::tr("Widget的事件过滤器");
47. }
48. return QWidget::eventFilter(watched, event);
49. }
50. void Widget::keyPressEvent(QKeyEvent *event)
51. {
52. qDebug()<<QObject::tr("Widget键盘按下事件");
53. }