qt-everywhere-src-5.15.1/qtbase/src/gui/doc/snippets/droparea.cpp

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#include <QtGui>

#include "droparea.h"

DropArea::DropArea(QWidget *parent)
    : QLabel(parent)
{
    setMinimumSize(200, 200);
    setFrameStyle(QFrame::Sunken | QFrame::StyledPanel);
    setAlignment(Qt::AlignCenter);
    setAcceptDrops(true);
    setAutoFillBackground(true);
    clear();
}

void DropArea::dragEnterEvent(QDragEnterEvent *event)
{
    setText(tr("<drop content>"));
    setBackgroundRole(QPalette::Highlight);

    event->acceptProposedAction();
    emit changed(event->mimeData());
}

void DropArea::dragMoveEvent(QDragMoveEvent *event)
{
    event->acceptProposedAction();
}

void DropArea::dropEvent(QDropEvent *event)
{
    const QMimeData *mimeData = event->mimeData();

    if (mimeData->hasImage()) {
        setPixmap(qvariant_cast<QPixmap>(mimeData->imageData()));
    } else if (mimeData->hasHtml()) {
        setText(mimeData->html());
        setTextFormat(Qt::RichText);
    } else if (mimeData->hasText()) {
        setText(mimeData->text());
        setTextFormat(Qt::PlainText);
    } else {
        setText(tr("Cannot display data"));
    }

    setBackgroundRole(QPalette::Dark);
    event->acceptProposedAction();
}

//![0]
void DropArea::paste()
{
    const QClipboard *clipboard = QApplication::clipboard();
    const QMimeData *mimeData = clipboard->mimeData();

    if (mimeData->hasImage()) {
        setPixmap(qvariant_cast<QPixmap>(mimeData->imageData()));
    } else if (mimeData->hasHtml()) {
        setText(mimeData->html());
        setTextFormat(Qt::RichText);
    } else if (mimeData->hasText()) {
        setText(mimeData->text());
        setTextFormat(Qt::PlainText);
    } else {
        setText(tr("Cannot display data"));
    }
//![0]

    emit changed(mimeData);
    setBackgroundRole(QPalette::Dark);
    //event->acceptProposedAction();
}

void DropArea::dragLeaveEvent(QDragLeaveEvent *event)
{
    clear();
    event->accept();
}

void DropArea::clear()
{
    setText(tr("<drop content>"));
    setBackgroundRole(QPalette::Dark);

    emit changed();
}

QPixmap DropArea::extractPixmap(const QByteArray &data, const QString &format)
{
    const QList<QByteArray> imageFormats = QImageReader::supportedImageFormats();
    QPixmap pixmap;

    for (const QByteArray &imageFormat : imageFormats) {
        if (format.mid(6) == QString(imageFormat)) {
            pixmap.loadFromData(data, imageFormat);
            break;
        }
    }
    return pixmap;
}