addStretch 布局关闭按钮显示在右下角

QPushButton*btn=newQPushButton("close",widget);

btn->setFixedSize(75,25);

QObject::connect(btn,SIGNAL(clicked()),widget,SLOT(close()));

//创建一弹簧

QSpacerItem*vSpacer=newQSpacerItem(22,100,QSizePolicy::Expanding,QSizePolicy::Minimum);

QVBoxLayout*rightLayout=newQVBoxLayout;

rightLayout->addItem(vSpacer);

rightLayout->addWidget(btn,1,Qt::AlignBottom);

QHBoxLayout*mainLayout=newQHBoxLayout;

mainLayout->addStretch(1);

mainLayout->addLayout(rightLayout);

widget->setLayout(mainLayout);

widget->show();