Qt-事件过滤及实例

    事件过滤器功能使得一个QObject对象可以监视另一个QObject对象中的事件，通过在一个QObject对象中安装事件过滤器，可以在事件到达该对象前捕获事件，从而起到监视该对象的作用。

    例如，实现按下按钮时，按钮上的文字为“Key Down”，松开按钮时，按钮上的文字为“Key Up”，创建一个QMainWindow窗口

1. mainwindow.h

#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include <QMainWindow>

class QPushButton;

namespace Ui {
class MainWindow;
}

class MainWindow : public QMainWindow
{
    Q_OBJECT

public:
    explicit MainWindow(QWidget *parent = nullptr);
    ~MainWindow();

private slots:
    bool eventFilter(QObject* watched, QEvent* event);

private:
    Ui::MainWindow *ui;

    QPushButton* m_button;
};

#endif // MAINWINDOW_H

2. mainwindow.cpp

#include "mainwindow.h"
#include "ui_mainwindow.h"
#include <QPushButton>
#include <QMouseEvent>

MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow)
{
    ui->setupUi(this);

    m_button = new QPushButton("Key Up", this);
    m_button->installEventFilter(this);
}

MainWindow::~MainWindow()
{
    delete ui;
}

bool MainWindow::eventFilter(QObject *watched, QEvent *event)
{
    if(watched == m_button)
    {
        if(event->type() == QEvent::MouseButtonPress)  //鼠标按下
        {
            QMouseEvent* mouseEvent = (QMouseEvent*)event;
            if(mouseEvent->buttons() & Qt::LeftButton)  //左键按下
            {
                m_button->setText("Left Key Down");
            }
            else if(mouseEvent->buttons() & Qt::MidButton)
            {
                m_button->setText("Middle Key Down");
            }
            else if(mouseEvent->buttons() & Qt::RightButton)
            {
                m_button->setText("Right Key Down");
            }
        }
        else if(event->type() == QEvent::MouseButtonRelease)  //鼠标释放
        {
            m_button->setText("Key Up");
        }
    }

    //将事件交给上层对话框
    return QObject::eventFilter(watched, event);
}

标签：event,Qt,实例,button,QObject,过滤,Key,include,MainWindow
来源： https://www.cnblogs.com/xiang-L/p/16035095.html