dragwidget.cpp Example File

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  #include <QtWidgets>

  #include "dragwidget.h"

  DragWidget::DragWidget(QWidget *parent)
      : QFrame(parent)
  {
      setMinimumSize(200, 200);
      setFrameStyle(QFrame::Sunken | QFrame::StyledPanel);
      setAcceptDrops(true);

      QLabel *boatIcon = new QLabel(this);
      boatIcon->setPixmap(QPixmap(":/images/boat.png"));
      boatIcon->move(10, 10);
      boatIcon->show();
      boatIcon->setAttribute(Qt::WA_DeleteOnClose);

      QLabel *carIcon = new QLabel(this);
      carIcon->setPixmap(QPixmap(":/images/car.png"));
      carIcon->move(100, 10);
      carIcon->show();
      carIcon->setAttribute(Qt::WA_DeleteOnClose);

      QLabel *houseIcon = new QLabel(this);
      houseIcon->setPixmap(QPixmap(":/images/house.png"));
      houseIcon->move(10, 80);
      houseIcon->show();
      houseIcon->setAttribute(Qt::WA_DeleteOnClose);
  }

  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();
      }
  }

  void DragWidget::mousePressEvent(QMouseEvent *event)
  {
      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());

      QMimeData *mimeData = new QMimeData;
      mimeData->setData("application/x-dnditemdata", itemData);

      QDrag *drag = new QDrag(this);
      drag->setMimeData(mimeData);
      drag->setPixmap(pixmap);
      drag->setHotSpot(event->pos() - child->pos());

      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);
      }
  }