6_2.EventFilter

• 消息的捕获

可以给某个窗口安装消息过滤器，之后经过该窗口的消息，都会先调用eventFilter函数过滤。

示例中显示了如何使用消息过滤器来过滤按钮被按下导致窗口被关闭 。可以注释掉信号与槽关联函数，但是安装消息过滤器会更方便。（捕获某个消息后 ，return true即可拦截该消息。return false则不拦截该消息）

• 在app中查看所有窗口的消息

派生app类，重载notify函数，可以查看所有object对应得所有消息。

• 窗口间发送自定义消息

QApplication::postEvent(this,new QEvent(QEvent::User));

#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

#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);
}

#ifndef MYWIDGET_H
#define MYWIDGET_H

#include <QWidget>
#include <QPushButton>
class MyWidget : public QWidget
{
    Q_OBJECT
public:
    explicit MyWidget(QWidget *parent = 0);

    QPushButton* _button;
    bool eventFilter(QObject *, QEvent *);
    bool event(QEvent *);

signals:

public slots:

};

#endif // MYWIDGET_H

#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(o == (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";
   // app.sendEvent(&w, )

    return app.exec();
}