dragwidget.cpp Example File

/****************************************************************************
**
** Copyright (C) 2016 The Qt Company Ltd.
** Contact: https://www.qt.io/licensing/
**
** This file is part of the examples of the Qt Toolkit.
**
** $QT_BEGIN_LICENSE:BSD$
** Commercial License Usage
** Licensees holding valid commercial Qt licenses may use this file in
** accordance with the commercial license agreement provided with the
** Software or, alternatively, in accordance with the terms contained in
** a written agreement between you and The Qt Company. For licensing terms
** and conditions see https://www.qt.io/terms-conditions. For further
** information use the contact form at https://www.qt.io/contact-us.
**
** BSD License Usage
** Alternatively, 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.
**   * Neither the name of The Qt Company Ltd nor the names of its
**     contributors may be used to endorse or promote products derived
**     from this software without specific prior written permission.
**
**
** THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
** "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
** LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
** A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
** OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
** SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
** LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
** DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
** THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
** (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
** OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE."
**
** $QT_END_LICENSE$
**
****************************************************************************/
#include <QtWidgets>
#include "dragwidget.h"
static QLabel *createDragLabel(const QString &text, QWidget *parent)
{
    QLabel *label = new QLabel(text, parent);
    label->setAutoFillBackground(true);
    label->setFrameShape(QFrame::Panel);
    label->setFrameShadow(QFrame::Raised);
    return label;
}
static QString hotSpotMimeDataKey() { return QStringLiteral("application/x-hotspot"); }
DragWidget::DragWidget(QWidget *parent)
    : QWidget(parent)
{
    QFile dictionaryFile(QStringLiteral(":/dictionary/words.txt"));
    dictionaryFile.open(QIODevice::ReadOnly);
    QTextStream inputStream(&dictionaryFile);
    int x = 5;
    int y = 5;
    while (!inputStream.atEnd()) {
        QString word;
        inputStream >> word;
        if (!word.isEmpty()) {
            QLabel *wordLabel = createDragLabel(word, this);
            wordLabel->move(x, y);
            wordLabel->show();
            wordLabel->setAttribute(Qt::WA_DeleteOnClose);
            x += wordLabel->width() + 2;
            if (x >= 245) {
                x = 5;
                y += wordLabel->height() + 2;
            }
        }
    }
    setAcceptDrops(true);
    setMinimumSize(400, qMax(200, y));
    setWindowTitle(tr("Draggable Text"));
}
void DragWidget::dragEnterEvent(QDragEnterEvent *event)
{
    if (event->mimeData()->hasText()) {
        if (event->source() == this) {
            event->setDropAction(Qt::MoveAction);
            event->accept();
        } else {
            event->acceptProposedAction();
        }
    } else {
        event->ignore();
    }
}
void DragWidget::dropEvent(QDropEvent *event)
{
    if (event->mimeData()->hasText()) {
        const QMimeData *mime = event->mimeData();
        QStringList pieces = mime->text().split(QRegularExpression(QStringLiteral("\\s+")),
                             QString::SkipEmptyParts);
        QPoint position = event->pos();
        QPoint hotSpot;
        QByteArrayList hotSpotPos = mime->data(hotSpotMimeDataKey()).split(' ');
        if (hotSpotPos.size() == 2) {
            hotSpot.setX(hotSpotPos.first().toInt());
            hotSpot.setY(hotSpotPos.last().toInt());
        }
        for (const QString &piece : pieces) {
            QLabel *newLabel = createDragLabel(piece, this);
            newLabel->move(position - hotSpot);
            newLabel->show();
            newLabel->setAttribute(Qt::WA_DeleteOnClose);
            position += QPoint(newLabel->width(), 0);
        }
        if (event->source() == this) {
            event->setDropAction(Qt::MoveAction);
            event->accept();
        } else {
            event->acceptProposedAction();
        }
    } else {
        event->ignore();
    }
    for (QWidget *widget : findChildren<QWidget *>()) {
        if (!widget->isVisible())
            widget->deleteLater();
    }
}
void DragWidget::mousePressEvent(QMouseEvent *event)
{
    QLabel *child = qobject_cast<QLabel*>(childAt(event->pos()));
    if (!child)
        return;
    QPoint hotSpot = event->pos() - child->pos();
    QMimeData *mimeData = new QMimeData;
    mimeData->setText(child->text());
    mimeData->setData(hotSpotMimeDataKey(),
                      QByteArray::number(hotSpot.x()) + ' ' + QByteArray::number(hotSpot.y()));
    qreal dpr = window()->windowHandle()->devicePixelRatio();
    QPixmap pixmap(child->size() * dpr);
    pixmap.setDevicePixelRatio(dpr);
    child->render(&pixmap);
    QDrag *drag = new QDrag(this);
    drag->setMimeData(mimeData);
    drag->setPixmap(pixmap);
    drag->setHotSpot(hotSpot);
    Qt::DropAction dropAction = drag->exec(Qt::CopyAction | Qt::MoveAction, Qt::CopyAction);
    if (dropAction == Qt::MoveAction)
        child->close();
}