鼠标事件不会传递给QGraphicsItemGroup中添加的QPushButton

Question

我在Windows 7旗舰版x64上使用Qt 4.8.3（32位）。

在QGraphicsScene子类的构造函数中，我有：

QGraphicsItemGroup *point_table = new QGraphicsItemGroup;
addItem(point_table);

稍后在构造函数中：

QPushButton *button = new QPushButton("Call++");
QGraphicsProxyWidget *inc_button = addWidget(button);
connect(button, SIGNAL(clicked()), this, SLOT(onCallIncrease()));

单击按钮时会调用

onCallIncrease()。但是，如果我将inc_button添加到point_table，则onCallIncrease()不会被调用。

QPushButton *button = new QPushButton("Call++");
QGraphicsProxyWidget *inc_button = addWidget(button);
point_table->addToGroup(inc_button);
connect(button, SIGNAL(clicked()), this, SLOT(onCallIncrease())); // doesn't work

即使我手动设置为接受鼠标左键：

QPushButton *button = new QPushButton("Call++");
QGraphicsProxyWidget *inc_button = addWidget(button);
inc_button->setAcceptedMouseButtons(Qt::LeftButton);
point_table->setAcceptedMouseButtons(Qt::LeftButton);
point_table->addToGroup(inc_button);
connect(button, SIGNAL(clicked()), this, SLOT(onCallIncrease())); // doesn't work

单击鼠标左键不会调用

onCallIncrease()。为什么会这样？