Qt 重写了QLineEdit的focusInEvent(QFocusEvent *e) ，提示without object错误
需要焦点移入QLineEdit后做些处理，查看了文档说可以重写focusInEvent(QFocusEvent *e)

但是总是会提示cannot call member function 'virtual void QLineEdit::focusInEvent(QFocusEvent*)' without object 错误。
代码非常简单，如下：

.h

#include <QMainWindow>
#include <QFocusEvent>
#include <QLineEdit>

namespace Ui {
class MainWindow;
}

class MainWindow : public QMainWindow
{
    Q_OBJECT
    
public:
    explicit MainWindow(QWidget *parent = 0);
    ~MainWindow();

protected:
    void focusInEvent(QFocusEvent *);
    
private:
    Ui::MainWindow *ui;
};

.cpp

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

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

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


void MainWindow::focusInEvent(QFocusEvent *e)
{
    QLineEdit::focusInEvent(e);
    qDebug()<<"??????????";
}

编译总是提示：error: cannot call member function 'virtual void QLineEdit::focusInEvent(QFocusEvent*)' without object

并且获取焦点后也没有什么反应。。求指点。谢谢
[解决办法]
你现在在子类化QMainWindow，而你需要的是子类化 QLineEdit
[解决办法]
你要重写QLineEdit
[解决办法]
如果只是捕捉这一个事件的话，事件过滤器可能更合适一些