- Qt 5.5
- Qt Widgets
- Draggable Icons Example
- dragwidget.cpp Example File
- Qt 5.5.1 Reference Documentation

# dragwidget.cpp Example File

draganddrop/draggableicons/dragwidget.cpp

    /****************************************************************************
    **
    ** Copyright (C) 2015 The Qt Company Ltd.
    ** Contact: http://www.qt.io/licensing/
    **
    ** This file is part of the examples of the Qt Toolkit.
    **
    ** $QT_BEGIN_LICENSE:BSD$
    ** You may use this file under the terms of the BSD license as follows:
    **
    ** "Redistribution and use in source and binary forms, with or without
    ** modification, are permitted provided that the following conditions are
    ** met:
    **   * Redistributions of source code must retain the above copyright
    **     notice, this list of conditions and the following disclaimer.
    **   * Redistributions in binary form must reproduce the above copyright
    **     notice, this list of conditions and the following disclaimer in
    **     the documentation and/or other materials provided with the
    **     distribution.
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    **     contributors may be used to endorse or promote products derived
    **     from this software without specific prior written permission.
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    ** "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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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);
        }
    }