QT eventFilter使用问题

//Widget.h 中声明了eventFilter 函数

protected:

    bool eventFilter(QObject *, QEvent *);



//在Widget.cpp中使用的时候出现程序异常结束

#include "widget.h"

#include "ui_widget.h"

#include<QEvent>

#include <QMouseEvent>

#include<QDebug>

Widget::Widget(QWidget *parent) :

    QWidget(parent),

    ui(new Ui::Widget)

{

    ui->setupUi(this);

    ui->label->installEventFilter(this);

    ui->label->setMouseTracking(true);

}



Widget::~Widget()

{

    delete ui;

}

bool Widget::eventFilter(QObject *obj, QEvent *e)

{

    if(ui->label==obj)

    {

        if(e==NULL)

        {

            qDebug()<<"NULL string";

        QMouseEvent *env=static_cast<QMouseEvent *>(e);

        if(e->type()==QEvent::MouseMove)

        {

                ui->label->setText(QString("Mouse Move:(%1,%2)").arg(env->x()).arg(env->y()));

                return true;

        }

        }

    }

    return eventFilter(obj,e);

}