简单的QGraphicsView代码的异常是啥_QT开发

简单的QGraphicsView代码的错误是啥
如附件中的工程，就希望能够添加一个形状，但直接是在Designer中设计的QGraphicsView中显示出来，怎么总是无法显示呢？？

我感觉view和scene的关系好像没有搞懂，但有觉得差不多了，木乱中。

谢谢。

mainwindowdialog.cpp

C/C++ code

#include "mainwindowdialog.h"#include "ui_mainwindowformdialog.h"#include <QtGui>MainWindowDialog::MainWindowDialog(QWidget *parent) :    QMainWindow(parent),    ui(new Ui::MainWindowFormDialog){    ui->setupUi(this);    viewer = ui->mwGraphicsView;}MainWindowDialog::~MainWindowDialog(){    delete ui;}void MainWindowDialog::on_action_New_triggered(){    //Settings, Nothing???    viewer->setForegroundBrush(QColor(0, 200, 00, 50));    viewer->setBackgroundBrush(QPixmap("./GruBear03.png"));    //[color=#FF0000]Error here..[/color].    //QGraphicsRectItem *recItem = new QGraphicsRectItem(0, 0, 100, 60);    //viewer->scene()->addItem(recItem);    //Error}

mainwindowdialog.h

C/C++ code

#ifndef MAINWINDOWDIALOG_H#define MAINWINDOWDIALOG_H#include <QMainWindow>namespace Ui {class MainWindowFormDialog;}class MainWindowDialog : public QMainWindow{    Q_OBJECT    public:    explicit MainWindowDialog(QWidget *parent = 0);    ~MainWindowDialog();    private slots:    void on_action_New_triggered();private:    Ui::MainWindowFormDialog *ui;    //view    class QGraphicsView *viewer;};#endif // MAINWINDOWDIALOG_H

main.cpp

C/C++ code

#include <QtGui/QApplication>#include "mainwindowdialog.h"int main(int argc, char *argv[]){    QApplication a(argc, argv);    MainWindowDialog w;    w.show();        return a.exec();}

pro 文件

C/C++ code

#-------------------------------------------------## Project created by QtCreator 2012-09-28T15:40:57##-------------------------------------------------QT       += core guiTARGET = GraViewTEMPLATE = appSOURCES += main.cpp\        mainwindowdialog.cppHEADERS  += mainwindowdialog.hFORMS    += mainwindowformdialog.ui

------解决方案--------------------
一般是构造函数中这样

m_scene = new QGraphicsScene();
ui->graphicsView->setScene(m_scene);

这样的哈。。。。