事例如下：创建了QMenu菜单，设置透明度的效果：

设置前：

myMenu = new QMenu;

myMenu->setWindowOpacity(1);//调节菜单的透明度，范围是1到0，1（完全不透明）到0（完全透明）,如果不进行设置，默认的是1，可以把1改成零点几看一下效果

QAction* openAction = new QAction(QString::fromLocal8Bit("打开文件"),NULL);

connect(openAction,SIGNAL(triggered()),this,SIGNAL(signal_open_file()));

myMenu->addAction(openAction);

QAction* registerAction = new QAction(QString::fromLocal8Bit("注册文件"),NULL);

connect(registerAction,SIGNAL(triggered()),this,SIGNAL(signal_register()));

myMenu->addAction(registerAction);

QAction* closeAction = new QAction(QString::fromLocal8Bit("关闭文件"),NULL);

connect(closeAction,SIGNAL(triggered()),this,SIGNAL(signal_close()));

myMenu->addAction(closeAction);

myMenu->setStyleSheet("QMenu {background-color: gray ;border: 1px solid black;color: white}QMenu::item:selected {background-color: black }");