我做了一个窗口，把它设为了无边框，这样就无法实现拖动了。我网上看了好久，是要重写
void mousePressEvent (QMouseEvent *event);
    void mouseReleaseEvent(QMouseEvent *event);
    void mouseMoveEvent(QMouseEvent *event);
这三个函数，我重写了，但拖动窗口的时候程序就崩掉了，不知道为什么？
源码如下：
头文件
#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include <QMainWindow>
#include <QMouseEvent>

namespace Ui {
class MainWindow;
}

class MainWindow : public QMainWindow
{
    Q_OBJECT

public:
    explicit MainWindow(QWidget *parent = 0);
    ~MainWindow();
protected:
    void mousePressEvent (QMouseEvent *event);
    void mouseReleaseEvent(QMouseEvent *event);
    void mouseMoveEvent(QMouseEvent *event);

private:
    Ui::MainWindow *ui;
    bool shouldMove;        //是否要改变窗口位置
    QPoint *formerMainPos;      //移动前窗口的位置
    QPoint *formerMousePos;  //第一次按下左键时鼠标的位置

};

#endif // MAINWINDOW_H

CPP文件：
#include "mainwindow.h"
#include "ui_mainwindow.h"

MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow)
{
    ui->setupUi(this);
    this->setMouseTracking(true);
    this->shouldMove=false;
    this->setWindowFlags(Qt::FramelessWindowHint);
}

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

void MainWindow::mousePressEvent (QMouseEvent *event)
    {
        if (event->button()==Qt::LeftButton){
            shouldMove = true;
            *formerMainPos =this->pos();
            *formerMousePos = event->globalPos();
            event->accept();
        }
    }

void MainWindow::mouseReleaseEvent(QMouseEvent *event){
        if (event->button()==Qt::LeftButton){
            shouldMove = false;
        }
    }

void MainWindow::mouseMoveEvent ( QMouseEvent * event )
    {
        QPoint point = event->globalPos();

        if (shouldMove&&(event->button()==Qt::LeftButton))
        {
            int x = point.x()-formerMousePos->x();
            int y = point.y()-formerMousePos->y();
            this->move(formerMainPos->x()+x,formerMainPos->y()+y);
            event->accept();
        }
    }

没多少分了，大神莫嫌弃。

没有大神帮忙吗？