Qt事件学习

一、创建Qt gui应用对应的源码：

//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");
}