Qt处理焦点事件(获得焦点，失去焦点)

#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include <QMainWindow>

namespace Ui {
class MainWindow;
}

class MainWindow : public QMainWindow
{
    Q_OBJECT

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

private:
    Ui::MainWindow *ui;

    bool eventFilter(QObject *watched, QEvent *event);
};

#endif // MAINWINDOW_H

#include "mainwindow.h"
#include "ui_mainwindow.h"

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

MainWindow::~MainWindow()
{
    delete ui;
}
bool MainWindow::eventFilter(QObject *watched, QEvent *event)
{
    if (watched == ui->lineEdit && event->type() == QEvent::FocusOut)
    {
        ui->lineEdit->setFocus();
        return true;
    }
    return QWidget::eventFilter(watched, event);
}