用QWidget实现直线拖动效果

1. 环境

Qt 5.12 +VS2015 community

2. 效果

QWidget部件上拖动直线，达到类似扫描的效果

3.主要代码

主要是要重载几个事件，如鼠标事件和拖动事件等，可以参考到QT官方例程DraggableIcons。

Widget::Widget(QWidget *parent): QWidget(parent),
    ui(new Ui::Widget)
{
    ui->setupUi(this);
    setAcceptDrops(true);

    mPixmap = QSharedPointer<QPixmap> (new QPixmap(width(), 2));
    mPixmap->fill(Qt::red);

    m_pHLine = new QFrame(this);
    m_pHLine->setMinimumWidth(width());

    m_pHLine->setFrameStyle(QFrame::HLine | QFrame::Plain);
    m_pHLine->setAttribute(Qt::WA_DeleteOnClose);
}

Widget::~Widget()
{
    delete ui;
}

void Widget::resizeEvent(QResizeEvent *event)
{
    Q_UNUSED(event);
    mPixmap.reset(new QPixmap(event->size().width(), 2));
    mPixmap->fill(Qt::red);
}

void Widget::dragEnterEvent(QDragEnterEvent *event)
{
    if (event->source() == this) {
        event->setDropAction(Qt::MoveAction);
        event->accept();
    } else {
        event->acceptProposedAction();
    }

}

void Widget::dragMoveEvent(QDragMoveEvent *event)
{
    if (event->source() == this) {
        event->setDropAction(Qt::MoveAction);
        event->accept();
    } else {
        event->acceptProposedAction();
    }
}

void Widget::dropEvent(QDropEvent *event)
{

    QFrame * hline = new QFrame(this);
    hline->setMinimumWidth(width());
    hline->setFrameStyle(QFrame::HLine | QFrame::Plain);
    hline->setAttribute(Qt::WA_DeleteOnClose);

    hline->move(0.0, event->pos().y() );
    hline->show();

    if (event->source() == this) {
        event->setDropAction(Qt::MoveAction);
        event->accept();
    } else {
        event->acceptProposedAction();
    }
}

void Widget::mousePressEvent(QMouseEvent *event)
{
    QFrame *child = static_cast<QFrame*>(childAt(event->pos()));
    if (!child)
        return;

    QDrag *drag = new QDrag(this);
    drag->setMimeData( new QMimeData()); /// 必须设置MimeData才能实现拖动的效果，哪怕是个空的
    drag->setPixmap(*mPixmap.data());
    drag->setHotSpot(event->pos() - child->pos());


    if (drag->exec(Qt::CopyAction | Qt::MoveAction, Qt::CopyAction) == Qt::MoveAction) {
        child->close();
    }
}