QWidget does not receive mouse enter event when unactiver

//代码占位符
#include "widget.h"
#include "./ui_widget.h"Widget::Widget(QWidget *parent)
    : QWidget(parent)
    , ui(new Ui::Widget)
{
    ui->setupUi(this);
    setWindowFlags(Qt::FramelessWindowHint | Qt::WindowStaysOnTopHint);
    setMouseTracking(true);
}Widget::~Widget()
{
    delete ui;
}void Widget::enterEvent(QEnterEvent* event){
    qInfo() << "enter event";
    QWidget::enterEvent(event);
}