QT事件处理（五）–notify()

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Qt处理事件的第五种方式：”继承QApplication并重新实现notify()函数”。Qt调用QApplication来发送一个事件，重新实现notify()函数是在事件过滤器得到所有事件之前获得它们的唯一方法。事件过滤器使用更为便利。因为可以同时有多个事件过滤器。而notify()函数只有一个。

重新实现的QApplication类MyApplication的头文件myapplication.h如下：

 #ifndef MYAPPLICATION_H
#define MYAPPLICATION_H
 
#include <QApplication>
#include <QEvent>
 
class MyApplication : public QApplication
{
public:
    MyApplication(int & argc, char ** argv);
 
public:
    bool notify(QObject *receiver, QEvent *e);
};
 
#endif

myapplication.cpp文件如下：

 #include "myapplication.h"
#include <QMouseEvent>
 
MyApplication::MyApplication(int & argc, char ** argv) : QApplication(argc, argv)
{
}
 
 bool MyApplication::notify(QObject *receiver, QEvent *e)
 {
     //屏蔽MouseButtonPress、MouseButtonRelease和MouseMove事件
     if (e->type() == QEvent::MouseButtonPress || e->type() == QEvent::MouseButtonRelease || e->type() == QEvent::MouseMove)
     {
        return true;
     }
     return QApplication::notify(receiver, e);
 }

mainwindow.h文件如下：

 #ifndef MAINWINDOW_H
#define MAINWINDOW_H
 
#include <QtGui/QMainWindow>
#include <QPushButton>
#include <QMouseEvent>
 
class MainWindow : public QMainWindow
{
    Q_OBJECT
    
public:
    MainWindow(QWidget *parent = 0);
    ~MainWindow();
protected:
    bool eventFilter(QObject *obj, QEvent *e);
private:
    QPushButton *button;
};
 
#endif

mainwindow.cpp文件如下：

 #include "mainwindow.h"
 
MainWindow::MainWindow(QWidget *parent)
    : QMainWindow(parent)
{
    button = new QPushButton;
    this->setCentralWidget(button);
}
 
MainWindow::~MainWindow()
{
 
}
 
bool MainWindow::eventFilter(QObject *obj, QEvent *e)
{
    if (obj == button)         //响应button的MouseButtonPress和MouseButtonRelease事件
    {
        if (e->type() == QEvent::MouseButtonPress)
        {
            QMouseEvent *event = static_cast<QMouseEvent*> (e);
            button->setText(QString("Press: %1, %2").arg(QString::number(event->x()), QString::number(event->y())));
            return true;
        }
        else if (e->type() == QEvent::MouseButtonRelease)
        {
            QMouseEvent *event = static_cast<QMouseEvent*> (e);
            button->setText(QString("Release: %1, %2").arg(QString::number(event->x()), QString::number(event->y())));
            return true;
        }
        else
        {
            return false;
        }
    }
 
    return QMainWindow::eventFilter(obj, e);
}

main.cpp文件如下：

 #include <QtGui/QApplication>
#include <QtCore/QTextCodec>
#include "mainwindow.h"
#include "myapplication.h"
 
int main(int argc, char *argv[])
{
    MyApplication a(argc, argv);
    QTextCodec::setCodecForTr(QTextCodec::codecForName("gb18030"));
    MainWindow mainwindow;
    a.installEventFilter(&mainwindow);  //为QApplication注册过滤器
    mainwindow.setWindowTitle(QObject::tr("继承QApplication并重新实现notify()函数"));
    mainwindow.resize(400, 200);
    mainwindow.show();
 
    return a.exec();
}

运行程序，可以发现button不管是点击、释放还是拖动鼠标，都不会显示任何文本。因为我们已经子类化QApplication，事件在到达QApplication的事件过滤器之前，会先到达QApplication的notify()函数，我们已经在子类化的MyApplication中屏蔽了MouseButtonPress、MouseButtonRelease事件。所以为MyApplication对象注册的事件过滤器不起作用。程序运行界面为：

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Qt

发表至： Qt

2016-05-12

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QT事件处理(四)–QApplication中注册事件过滤器

	`#ifndef MYAPPLICATION_H`
	#define MYAPPLICATION_H

	#include <QApplication>
	#include <QEvent>

	class MyApplication : public QApplication
	{
	public:
	MyApplication(int & argc, char ** argv);

	public:
	bool notify(QObject receiver, QEvent e);
	};

	#endif

	`#include "myapplication.h"`
	#include <QMouseEvent>

	MyApplication::MyApplication(int & argc, char ** argv) : QApplication(argc, argv)
	{
	}

	bool MyApplication::notify(QObject receiver, QEvent e)
	{
	//屏蔽MouseButtonPress、MouseButtonRelease和MouseMove事件
	if (e->type() == QEvent::MouseButtonPress \|\| e->type() == QEvent::MouseButtonRelease \|\| e->type() == QEvent::MouseMove)
	{
	return true;
	}
	return QApplication::notify(receiver, e);
	}

	`#ifndef MAINWINDOW_H`
	#define MAINWINDOW_H

	#include <QtGui/QMainWindow>
	#include <QPushButton>
	#include <QMouseEvent>

	class MainWindow : public QMainWindow
	{
	Q_OBJECT

	public:
	MainWindow(QWidget *parent = 0);
	~MainWindow();
	protected:
	bool eventFilter(QObject obj, QEvent e);
	private:
	QPushButton *button;
	};

	#endif

	`#include "mainwindow.h"`

	MainWindow::MainWindow(QWidget *parent)
	: QMainWindow(parent)
	{
	button = new QPushButton;
	this->setCentralWidget(button);
	}

	MainWindow::~MainWindow()
	{

	}

	bool MainWindow::eventFilter(QObject obj, QEvent e)
	{
	if (obj == button) //响应button的MouseButtonPress和MouseButtonRelease事件
	{
	if (e->type() == QEvent::MouseButtonPress)
	{
	QMouseEvent event = static_cast<QMouseEvent> (e);
	button->setText(QString("Press: %1, %2").arg(QString::number(event->x()), QString::number(event->y())));
	return true;
	}
	else if (e->type() == QEvent::MouseButtonRelease)
	{
	QMouseEvent event = static_cast<QMouseEvent> (e);
	button->setText(QString("Release: %1, %2").arg(QString::number(event->x()), QString::number(event->y())));
	return true;
	}
	else
	{
	return false;
	}
	}

	return QMainWindow::eventFilter(obj, e);
	}

	`#include <QtGui/QApplication>`
	#include <QtCore/QTextCodec>
	#include "mainwindow.h"
	#include "myapplication.h"

	int main(int argc, char *argv[])
	{
	MyApplication a(argc, argv);
	QTextCodec::setCodecForTr(QTextCodec::codecForName("gb18030"));
	MainWindow mainwindow;
	a.installEventFilter(&mainwindow); //为QApplication注册过滤器
	mainwindow.setWindowTitle(QObject::tr("继承QApplication并重新实现notify()函数"));
	mainwindow.resize(400, 200);
	mainwindow.show();

	return a.exec();
	}