Qt事件学习

一、创建Qt gui应用对应的源码：

点击(此处)折叠或打开

 //mylineedit.h
 #ifndef MYLINEEDIT_H
 #define MYLINEEDIT_H

 #include <QWidget>
 #include <QLineEdit>

 class MyLineEdit : public QLineEdit
 {
 public:
     explicit MyLineEdit(QWidget *parent = 0);
 protected:
     void keyPressEvent(QKeyEvent *event);
 };

 #endif // MYLINEEDIT_H


 //mylineedit.cpp
 #include "mylineedit.h"
 #include <QLineEdit>
 #include <QDebug>
 #include <QKeyEvent>

 MyLineEdit::MyLineEdit(QWidget *parent):QLineEdit(parent)
 {

 }

 void MyLineEdit::keyPressEvent(QKeyEvent *event)
 {
     qDebug() << QObject::tr("MyLineEdit键盘按下事件");
 }

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

 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：

 bool event(QEvent *event);

然后定义：

 bool MyLineEdit::event(QEvent *event)
 {
     if(event->type() == QEvent::KeyPress)
         qDebug()<<QObject::tr("MylineEdit的event()函数");
     return QLineEdit::event(event);
 }

四、第四次修改

widget.h中public申明：

 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：

 lineEdit->installEventFilter(this); //在widget上为lineEdit安装事件过滤器

 bool Widget::eventFilter(QObject *watched, QEvent *event)
 {
     if(watched==lineEdit) {
         if(event->type()==QEvent::KeyPress)
             qDebug()<<QObject::tr("Widget的事件过滤器");
     }
     return QWidget::eventFilter(watched, event);
 }

五、最后的源码：
mylineedit:

 //mylineedit.h
 #ifndef MYLINEEDIT_H
 #define MYLINEEDIT_H

 #include <QWidget>
 #include <QLineEdit>

 class MyLineEdit : public QLineEdit
 {
 public:
     explicit MyLineEdit(QWidget *parent = 0);
     bool event(QEvent *event);

 protected:
     void keyPressEvent(QKeyEvent *event);
 };

 #endif // MYLINEEDIT_H


 //mylineedit.cpp
 #include "mylineedit.h"
 #include <QLineEdit>
 #include <QDebug>
 #include <QKeyEvent>

 MyLineEdit::MyLineEdit(QWidget *parent):QLineEdit(parent)
 {

 }

 bool MyLineEdit::event(QEvent *event)
 {
     if(event->type() == QEvent::KeyPress)
         qDebug()<<QObject::tr("MylineEdit的event()函数");
     return QLineEdit::event(event);
 }

 void MyLineEdit::keyPressEvent(QKeyEvent *event)
 {
     qDebug() << QObject::tr("MyLineEdit键盘按下事件");
     QLineEdit::keyPressEvent(event);
     event->ignore();
 }

midget:

 //wdiget.h
 #ifndef WIDGET_H
 #define WIDGET_H

 #include <QWidget>

 class MyLineEdit;

 namespace Ui {
 class Widget;
 }

 class Widget : public QWidget
 {
     Q_OBJECT

 public:
     explicit Widget(QWidget *parent = 0);
     ~Widget();
     bool eventFilter(QObject *watched, QEvent *event);
 protected:
     void keyPressEvent(QKeyEvent *event);
 private:
     Ui::Widget *ui;
     MyLineEdit *lineEdit;
 };

 #endif // WIDGET_H


 //widget.cpp
 #include "widget.h"
 #include "ui_widget.h"
 #include "mylineedit.h"
 #include <QKeyEvent>
 #include <QDebug>

 Widget::Widget(QWidget *parent) :
     QWidget(parent),
     ui(new Ui::Widget)
 {
     lineEdit = new MyLineEdit(this);
     lineEdit->move(100, 100);
     lineEdit->installEventFilter(this); //在widget上为lineEdit安装事件过滤器
     ui->setupUi(this);
 }

 Widget::~Widget()
 {
     delete ui;
 }

 bool Widget::eventFilter(QObject *watched, QEvent *event)
 {
     if(watched==lineEdit) {
         if(event->type()==QEvent::KeyPress)
             qDebug()<<QObject::tr("Widget的事件过滤器");
     }
     return QWidget::eventFilter(watched, event);
 }

 void Widget::keyPressEvent(QKeyEvent *event)
 {
     qDebug()<<QObject::tr("Widget键盘按下事件");
 }

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