QScrollArea滚动条的问题 [复制链接]

        scrollAreaWidgetContents = new QWidget();
        scrollAreaWidgetContents->setObjectName(QString::fromUtf8("scrollAreaWidgetContents"));
        groupBox_2 = new QGroupBox();
        groupBox_2->setObjectName(QString::fromUtf8("groupBox_2"));
        groupBox_2->setGeometry(QRect(10, 10, 120, 100));
        groupBox_3 = new QGroupBox();
        groupBox_3->setObjectName(QString::fromUtf8("groupBox_3"));
        groupBox_3->setGeometry(QRect(10, 180, 120, 80));
        groupBox_4 = new QGroupBox();
        groupBox_4->setObjectName(QString::fromUtf8("groupBox_4"));
        groupBox_4->setGeometry(QRect(10, 300, 120, 80));
        scrollArea->setFocusPolicy(Qt::NoFocus);
        scrollArea->setFrameStyle(QFrame::NoFrame);
        QVBoxLayout* layout=new QVBoxLayout;
        layout->addWidget(groupBox_2);
        layout->addWidget(groupBox_3);
        layout->addWidget(groupBox_4);
        scrollAreaWidgetContents->setLayout(layout);
                                          scrollArea->setWidget(scrollAreaWidgetContents);


如上，我想在一个scrollArea中加入三个GroupBox,我想设定好GroupBox的大小和ScrollArea的大小，然后如果groupBox超过了scrollArea的大小就要自动显示滚动条，请问怎么做啊？
小弟新学QT，搞了一天了，搞不出来，请大家帮帮忙，谢谢大家了。