c
//代码片段
    QScrollArea *scrollArea = new QScrollArea(passWidget);
    scrollArea->setFixedSize(836, 266);
    scrollArea->move(0,32);
    scrollArea->setWidgetResizable(true);
    QWidget *allCredentialsWidget=new QWidget(scrollArea);
    allCredentialsWidget->setFixedSize(816, 0);
    scrollArea->setWidget(allCredentialsWidget);

解决方案：QScrollArea边框设为0
scrollArea->setFrameShape(QFrame::NoFrame);