qt中的QScrollArea没有滚动条

[weixin_38065734]

QVBoxLayout *e = new QVBoxLayout;
Form *w1 = new Form;//QWidget的子类
Form *w2 = new Form;
Form *w3 = new Form;

e->addWidget(w1);
e->addWidget(w2);
e->addWidget(w3);

ui->scrollAreaWidgetContents->setLayout(e);
ui->scrollArea->setHorizontalScrollBarPolicy(Qt::ScrollBarAlwaysOn);