3.QT事件处理，消息过滤器



1 
新建一个项目：06Event

新建cpp文件

06Event.pro

HEADERS
+=
\

MyWidget.h

SOURCES
+=
\

MyWidget.cpp

QT
+=
widgets gui

MyWidget.h

#ifndef
MYWIDGET_H

#define
MYWIDGET_H

#include
<QWidget>

#include
<QPushButton>

#include
<QLineEdit>

class
MyWidget
:
public
QWidget

{

Q_OBJECT

public:

explicit
MyWidget(QWidget
*parent
);

bool
event(QEvent
*);

void
mousePressEvent(QMouseEvent
*);

void
mouseReleaseEvent(QMouseEvent
*);

void
mouseMoveEvent(QMouseEvent
*);

/*不要用,因为它默认调用两次mousePressEvent*/

//void
mouseDoubleClickEvent(QMouseEvent
*);

void
keyPressEvent(QKeyEvent
*);

void
keyReleaseEvent(QKeyEvent
*);

void
closeEvent(QCloseEvent
*);

//void
showEvent(QShowEvent
*);

//void
hideEvent(QHideEvent
*);

void
paintEvent(QPaintEvent
*);

QPushButton*
button;

QLineEdit*
edit;

signals:

public
slots:

void
slotButtonClicked();

};

#endif
//
MYWIDGET_H

MyWidget.cpp

#include "MyWidget.h"

#include <QApplication>

#include <QEvent>

#include <QDebug>

#include <QMouseEvent>

#include <QKeyEvent>

#include <QVBoxLayout>

#include <QPainter>

MyWidget::MyWidget(QWidget *parent) :

    QWidget(parent)

{

//  QVBoxLayout* lay = new QVBoxLayout(this);

#if 0

    QPushButton* button2;

    lay->addWidget(button = new QPushButton("OK", this));

    lay->addWidget(button2 = new QPushButton("Button2"));

    //设置它为默认的焦点，当点击tab键之后可以切换焦点

    button->setDefault(true);

    // 鼠标不需要按下，mouseMove就能得到调用

    this->setMouseTracking(true);

    connect(button2, SIGNAL(clicked()), this, SLOT(slotButtonClicked()));

    connect(button, SIGNAL(clicked()), this, SLOT(slotButtonClicked()));

#endif

//    lay->addWidget(edit = new QLineEdit());

//    connect(edit, SIGNAL(returnPressed()), this, SLOT(slotButtonClicked()));

}

//通过这一句实现点击按钮的时候获得按钮上的text()内容

void MyWidget::slotButtonClicked()

{

    QLineEdit* button = (QLineEdit*)sender();

    qDebug() << button->text();

}

/* QApplication先得到->具体应该处理的窗口::event()->event()根据消息类型来调用具体的虚函数 */

/* 1）可以重载具体的虚函数，来实现对消息的响应

   2）可以重载event函数，用来处理或者截取消息 */

/* 截取消息 */

bool MyWidget::event(QEvent *ev)

{

    // 鼠标消息被截断

   // if(ev->type() == QEvent::MouseButtonPress)

     //   return true;

    ev->accept();

    return QWidget::event(ev);

}

/**

 * @brief MyWidget::closeEvent 窗口关闭的事件

 */

void MyWidget::closeEvent(QCloseEvent *)

{

    qDebug() << "closeEvent";

}

void MyWidget::paintEvent(QPaintEvent *)

{

    QPainter p(this);

    //通过下面的方式实现画线

    p.drawLine(QPoint(0, 0), QPoint(100, 100));

}

/**

 * @brief MyWidget::mousePressEvent 鼠标按下的事件

 * @param ev

 */

void MyWidget::mousePressEvent(QMouseEvent *ev)

{

#if 0

    QPoint pt = ev->pos();

    qDebug() << pt;

    //如果鼠标按下的是左键的处理

    if(ev->button() == Qt::LeftButton){}

    //如果按下的Shift键了

    if(ev->modifiers() == Qt::ShiftModifier)

    {

        qDebug() << "shift press";

    }

#endif

    //改进办法：先判断是否有左键，然后如果判断是否还按了Ctrl键

    if(ev->button() == Qt::LeftButton)

    {

        if(ev->modifiers() == Qt::ControlModifier)

        {

            // handle with Control;

            return;

        }

        // handle2 without control;

    } else {}

}

/**

 * @brief MyWidget::mouseReleaseEvent 鼠标释放的按键

 */

void MyWidget::mouseReleaseEvent(QMouseEvent *){}

/**

 * @brief MyWidget::mouseMoveEvent 鼠标移动的事件

 */

void MyWidget::mouseMoveEvent(QMouseEvent *)

{

    static int i=0;

    qDebug() << "mouse move"<< i++;

}

/**

 * @brief MyWidget::keyPressEvent 鼠标按下的事件，通过这个可以获得按下的键

 * @param ev

 */

void MyWidget::keyPressEvent(QKeyEvent *ev)

{

    ev->modifiers();

    int key = ev->key();

    qDebug() << key;

    char a = key;

    qDebug() << (char)a;

}

/**

 * @brief MyWidget::keyReleaseEvent 按键释放的事件

 */

void MyWidget::keyReleaseEvent(QKeyEvent *){}

int main(int argc, char* argv[])

{

    QApplication app(argc, argv);

    MyWidget w;

    w.show();

    return app.exec();

}

运行结果：

2 
QT消息过滤器

EventFilter.pro

HEADERS
+=
\

MyWidget.h
\

MyApplication.h

SOURCES
+=
\

MyWidget.cpp
\

MyApplication.cpp

QT
+=
widgets gui

MyWidget.h

#ifndef MYWIDGET_H

#define MYWIDGET_H

#include <QWidget>

#include <QPushButton>

class MyWidget : public QWidget

{

    Q_OBJECT

public:

    explicit MyWidget(QWidget *parent);

    QPushButton* _button;

    bool eventFilter(QObject *, QEvent *);

    bool event(QEvent *);

signals:

public slots:

};

#endif // MYWIDGET_H

MyWidget.cpp

#include "MyWidget.h"

#include <QPushButton>

#include <QEvent>

#include "MyApplication.h"

#include <QDebug>

#include <QApplication>

MyWidget::MyWidget(QWidget *parent) :

    QWidget(parent)

{

    QPushButton* button;

    button = new QPushButton("This button", this);

    connect(button, SIGNAL(clicked()), this, SLOT(close()));

    _button = button;

    /*button给自己安装了一个消息过滤器，那么经过button的消息，

     * 都先要调用它的过滤器的eventFilter函数*/

    button->installEventFilter(this);

}

bool MyWidget::eventFilter(QObject *o, QEvent *e)

{

#if 0

    if(0 == (QObject*)_button &&(

                e->type() == QEvent::MouseButtonRelease ||

                e->type() == QEvent::MouseButtonDblClick ||

                e->type() == QEvent::MouseButtonPress)) {

        return true;

    }

#endif

    return QWidget::eventFilter(o,e);

}

bool MyWidget::event(QEvent *e)

{

    if(e->type() == QEvent::User)

    {

        qDebug() << "User event is comming";

    }

    return QWidget::event(e);

}

int main(int argc,char *argv[])

{

    MyApplication app(argc,argv);

    MyWidget w;

    w.show();

    //发送一个Event给MyWidget

    qDebug() << "begin send";

    app.postEvent(&w,new QEvent(QEvent::User));

    qDebug() << "end send";

    return app.exec();

}

MyApplication.h

#ifndef MYAPPLICATION_H

#define MYAPPLICATION_H

#include <QApplication>

class MyApplication : public QApplication

{

    Q_OBJECT

public:

    MyApplication(int argc,char *argv[]):QApplication(argc,argv)

    {}

    bool notify(QObject *,QEvent *);

signals:

public slots:

};

#endif // MYAPPLICATION_H

MyApplication.cpp

#include "MyApplication.h"

#include <QEvent>

#include <QDebug>

bool MyApplication::notify(QObject *o, QEvent *e)

{

    if(this->topLevelWidgets().count()>0)

    {

        QWidget* mainWnd = this->topLevelWidgets().at(0);

        if(o==(QObject*)mainWnd && e->type() == QEvent::MouseButtonPress)

        {

            // do ...

            qDebug() << "mainwnd is clicked";

        }

    }

    return QApplication::notify(o, e);

}

运行结果：