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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