Qt事件处理机制3-事件函数的分发

Qt开发中，经常重写event函数和具体的事件处理函数，例如mousePressEvent、paintEvent等，那么这些具体的事件处理函数是怎样被调用的呢？答案是由继承自QObject的类中的event函数来处理事件分发。这里以间接继承自QWidget的派生类MyButton举例说明。

MyButton.h

#ifndef MYBUTTON_H
#define MYBUTTON_H#include <QPushButton>class MyButton : public QPushButton
{Q_OBJECT
public:MyButton(QWidget *parent = nullptr);~MyButton();protected:bool event(QEvent *e) override;void mousePressEvent(QMouseEvent *event) override;
};#endif // MYBUTTON_H

MyButton.cpp

#include "MyButton.h"
#include <QDebug>
#include <QEvent>
#include <QMouseEvent>
MyButton::MyButton(QWidget *parent) : QPushButton(parent)
{}MyButton::~MyButton()
{}bool MyButton::event(QEvent *e)
{if (e->type() == QEvent::MouseButtonPress){qDebug() << __FUNCTION__ << e->isAccepted();}return QPushButton::event(e);
}void MyButton::mousePressEvent(QMouseEvent *event)
{qDebug() << __FUNCTION__ << event->isAccepted();
}

MainWindow.h

#ifndef MAINWINDOW_H
#define MAINWINDOW_H#include <QMainWindow>namespace Ui {
class MainWindow;
}class MainWindow : public QMainWindow
{Q_OBJECTpublic:explicit MainWindow(QWidget *parent = nullptr);~MainWindow();protected:bool event(QEvent *e) override;void mousePressEvent(QMouseEvent *event) override;private:Ui::MainWindow *ui;
};#endif // MAINWINDOW_H

MainWindow.cpp

#include "MainWindow.h"
#include "ui_MainWindow.h"
#include <QDebug>
#include <QEvent>
#include <QMouseEvent>MainWindow::MainWindow(QWidget *parent) :QMainWindow(parent),ui(new Ui::MainWindow)
{ui->setupUi(this);
}MainWindow::~MainWindow()
{delete ui;
}bool MainWindow::event(QEvent *e)
{if (e->type() == QEvent::MouseButtonPress){qDebug() << __FUNCTION__ << e->isAccepted();}return QMainWindow::event(e);
}void MainWindow::mousePressEvent(QMouseEvent *event)
{qDebug() << __FUNCTION__ << event->isAccepted();
}

运行结果正常

MyButton::event true
MyButton::mousePressEvent true// 若如下修改MyButton::mousePressEvent函数
void MyButton::mousePressEvent(QMouseEvent *event)
{qDebug() << __FUNCTION__ << event->isAccepted();event->ignore();
}
那么运行结果为（该代码同时验证了上一篇文章所说的事件函数的传播）：
MyButton::event true
MyButton::mousePressEvent true
MainWindow::event true
MainWindow::mousePressEvent true

可以看到，QPushButton::event(e)函数里最终调用了具体事件处理函数mousePressEvent，该函数是在QWidget类的event函数中进行分发的（MyButton->QPushButton->QAbstractButton->QWidget层层调用event函数）。

补充：QWidget中，event函数主要负责事件分发

bool QWidget::event(QEvent *event)
{Q_D(QWidget);// ignore mouse and key events when disabledif (!isEnabled()) {switch(event->type()) {case QEvent::TabletPress:case QEvent::TabletRelease:case QEvent::TabletMove:case QEvent::MouseButtonPress:case QEvent::MouseButtonRelease:case QEvent::MouseButtonDblClick:case QEvent::MouseMove:case QEvent::TouchBegin:case QEvent::TouchUpdate:case QEvent::TouchEnd:case QEvent::TouchCancel:case QEvent::ContextMenu:case QEvent::KeyPress:case QEvent::KeyRelease:
#if QT_CONFIG(wheelevent)case QEvent::Wheel:
#endifreturn false;default:break;}}switch (event->type()) {case QEvent::MouseMove:mouseMoveEvent((QMouseEvent*)event);break;case QEvent::MouseButtonPress:mousePressEvent((QMouseEvent*)event);break;case QEvent::MouseButtonRelease:mouseReleaseEvent((QMouseEvent*)event);break;case QEvent::MouseButtonDblClick:mouseDoubleClickEvent((QMouseEvent*)event);break;...default:return QObject::event(event);}return true;
}