效果一：
这样的效果显然不是我们想要的，于是查了下Qt的帮助文档，增加一句代码：
ui->widget->layout()->setAlignment(Qt::AlignTop);效果如下：
Qt要想实现拖拽，一般重写以下函数：
protected: void dragEnterEvent(QDragEnterEvent *event) override; void dragMoveEvent(QDragMoveEvent *event) override; void dropEvent(QDropEvent *event) override; void mousePressEvent(QMouseEvent *event) override;下面是Qt自带拖拽例子部分代码：
void DragWidget::dragEnterEvent(QDragEnterEvent *event) { if (event->mimeData()->hasFormat("application/x-dnditemdata")) { if (event->source() == this) { event->setDropAction(Qt::MoveAction); event->accept(); } else { event->acceptProposedAction(); } } else { event->ignore(); } } void DragWidget::dragMoveEvent(QDragMoveEvent *event) { if (event->mimeData()->hasFormat("application/x-dnditemdata")) { if (event->source() == this) { event->setDropAction(Qt::MoveAction); event->accept(); } else { event->acceptProposedAction(); } } else { event->ignore(); } } void DragWidget::dropEvent(QDropEvent *event) { if (event->mimeData()->hasFormat("application/x-dnditemdata")) { QByteArray itemData = event->mimeData()->data("application/x-dnditemdata"); QDataStream dataStream(&itemData, QIODevice::ReadOnly); QPixmap pixmap; QPoint offset; dataStream >> pixmap >> offset; QLabel *newIcon = new QLabel(this); newIcon->setPixmap(pixmap); newIcon->move(event->pos() - offset); newIcon->show(); newIcon->setAttribute(Qt::WA_DeleteOnClose); if (event->source() == this) { event->setDropAction(Qt::MoveAction); event->accept(); } else { event->acceptProposedAction(); } } else { event->ignore(); } } //! [1] void DragWidget::mousePressEvent(QMouseEvent *event) { qDebug()<<"mousePressEvent"<<event->pos(); QLabel *child = static_cast<QLabel*>(childAt(event->pos())); if (!child) return; QPixmap pixmap = *child->pixmap(); QByteArray itemData; QDataStream dataStream(&itemData, QIODevice::WriteOnly); dataStream << pixmap << QPoint(event->pos() - child->pos()); //! [1] //! [2] QMimeData *mimeData = new QMimeData; mimeData->setData("application/x-dnditemdata", itemData); //! [2] //! [3] QDrag *drag = new QDrag(this); drag->setMimeData(mimeData); drag->setPixmap(pixmap); drag->setHotSpot(event->pos() - child->pos()); //! [3] QPixmap tempPixmap = pixmap; QPainter painter; painter.begin(&tempPixmap); painter.fillRect(pixmap.rect(), QColor(127, 127, 127, 127)); painter.end(); child->setPixmap(tempPixmap); if (drag->exec(Qt::CopyAction | Qt::MoveAction, Qt::CopyAction) == Qt::MoveAction) { child->close(); } else { child->show(); child->setPixmap(pixmap); } }实现效果如下：
