mousePressEvent不能与简单的QGraphicsView一起工作

我正在为大学的一个项目学习qt库。我试图创建一个简单的窗口，其中只有一个graphicsView，只有当光标在graphicsView内时才捕捉鼠标坐标。我首先尝试了mouseMoveEvent功能，但我无法让它工作。我用filter试过了，甚至和他们在一起也不起作用。我真的被这个东西卡住了，我在这里提供代码。问题是，mousePressEvent只在graphicsView之外工作，总是打印"1"。X:…Y:……"。我还为graphicsView创建了一个新类，如下所示:

//myGraphicsView.h
class MyGraphicsView : public QWidget
{
  Q_OBJECT
public:
  explicit MyGraphicsView(QWidget *parent = 0);
protected:
  void mousePressEvent(QMouseEvent* ev);
  bool eventFilter(QObject *obj, QEvent *e);
private:
  QGraphicsView *gv;
  QVBoxLayout *layout;
};

myGraphicView.cpp如下:

MyGraphicsView::MyGraphicsView(QWidget *parent) :
  QWidget(parent)
{
  gv = new QGraphicsView;
  layout = new QVBoxLayout;
  layout->addWidget(gv);
  setLayout(layout);
  gv->setMouseTracking(true);
  setMouseTracking(true);
}
void MyGraphicsView::mousePressEvent(QMouseEvent* event)
{
  qDebug() << "1. X: " << event->pos().x() << "; Y: " << event->pos().y() << endl;
}
bool MyGraphicsView::eventFilter(QObject *obj, QEvent *e)
{
  if (e->type() == QEvent::MouseButtonPress)
  {
    QMouseEvent *mouseEvent = (QMouseEvent *) e;
    qDebug() << "3. X: " << mouseEvent->x() << "; Y: " << mouseEvent->y() << endl;
    return true;
  }
  return false;
}

MainWindows.h如下:

    namespace Ui {
  class MainWindow;
}
class MainWindow : public QMainWindow
{
  Q_OBJECT
public:
  explicit MainWindow(QWidget *parent = 0);
  ~MainWindow();
protected:
  void mousePressEvent(QMouseEvent* ev);
private:
  Ui::MainWindow *ui;
  MyGraphicsView *v;
};

MainWindows.cpp如下:

MainWindow::MainWindow(QWidget *parent) :
  QMainWindow(parent),
  ui(new Ui::MainWindow)
{
  ui->setupUi(this);
  v = new MyGraphicsView;
  setMouseTracking(true);
  setCentralWidget(v);
  setWindowTitle("Simple mouse tracker");
  resize(300, 300);
}
MainWindow::~MainWindow()
{
  delete ui;
}
void MainWindow::mousePressEvent(QMouseEvent* ev)
{
  qDebug() << "2. X: " << ev->pos().x() << "; Y: " << ev->pos().y() << endl;
}