drop event becomes invalid

[lwz]

Using drag and drop to drag tree item to a QwtPlot, sometimes the event becomes invalid.

Please help. Below is the my code about drag and drop.

Drag starts:
 
void DataTree::mouseMoveEvent(QMouseEvent *event)
{
    if (m_currentItem) {
        QString name = m_currentItem->text(TITLE_COLUMN);
        QString seq = m_currentItem->text(ID_COLUMN);
        QString type = m_currentItem->text(TAG_COLUMN);
        QString code = m_currentItem->text(CODE_COLUMN);
 
        if (code.length() == 8) {
            QTreeWidgetItem *parentItem = m_currentItem->parent();
            QString fileName = parentItem->text(TAG_COLUMN);
 
            // Prepare for dragging
            QDrag *drag = new QDrag(this);
            QMimeData *mimeData = new QMimeData;
            QByteArray byteArray;
            QDataStream dataStream(&byteArray, QIODevice::WriteOnly);
            dataStream << fileName << name << seq << type;
 
            QSize size(30,30);
            QPixmap widgetImage = m_currentItem->icon(0).pixmap(size);
            drag->setPixmap(widgetImage);
            mimeData->setData("curveData/x-curveData", byteArray);
            drag->setMimeData(mimeData);
 
            drag->setHotSpot(QPoint(15,15));
            if (!(drag->exec(Qt::MoveAction) == Qt::MoveAction))
            {
//                event->ignore();
                ;
            }
        }
 
void DataTree::dragEnterEvent(QDragEnterEvent *event)
{
    if (event->mimeData()->hasFormat("curveData/x-curveData"))
    {
        event->acceptProposedAction();
        event->accept();
    }
    else
    {
        event->ignore();
    }
}
 
 
void DataTree::dragMoveEvent(QDragMoveEvent *event)
{
    if( event->mimeData()->hasFormat("curveData/x-curveData")){
           event->acceptProposedAction();
           event->accept();
       }
       else
       {
           event->ignore();
 
       }
 
}
 
Accept drop:
 
void Plot::dropEvent(QDropEvent *event)
{
 if (event->mimeData()->hasFormat("curveData/x-curveData")) {
        QByteArray byteArray = event->mimeData()->data("curveData/x-curveData");
        QDataStream dataStream(&byteArray, QIODevice::ReadOnly);
 
        QString fileName;
        QString name ;
        QString seq;
        QString type;
 
        dataStream >> fileName  >> name >> seq >> type;
 
        emit addCurve(fileName, name, seq, type, this);
        event->acceptProposedAction();
        event->accept();
 
    } else {
        event->ignore();
    }
}
 
void Plot::dragEnterEvent(QDragEnterEvent *event)
{
  if ( event->mimeData()->hasFormat("curveData/x-curveData")) {
        event->setDropAction(Qt::MoveAction);
        event->accept();
    } else {
        event->ignore();
 
    }
}
 
void Plot::dragMoveEvent(QDragMoveEvent *event)
{
 
    if (event->mimeData()->hasFormat("curveData/x-curveData")) {
        event->setDropAction(Qt::MoveAction);
        event->accept();
    } else {
        event->ignore();
    }
}

Drag starts:

void DataTree::mouseMoveEvent(QMouseEvent *event)
{
    if (m_currentItem) {
        QString name = m_currentItem->text(TITLE_COLUMN);
        QString seq = m_currentItem->text(ID_COLUMN);
        QString type = m_currentItem->text(TAG_COLUMN);
        QString code = m_currentItem->text(CODE_COLUMN);

        if (code.length() == 8) {
            QTreeWidgetItem *parentItem = m_currentItem->parent();
            QString fileName = parentItem->text(TAG_COLUMN);

            // Prepare for dragging
            QDrag *drag = new QDrag(this);
            QMimeData *mimeData = new QMimeData;
            QByteArray byteArray;
            QDataStream dataStream(&byteArray, QIODevice::WriteOnly);
            dataStream << fileName << name << seq << type;

            QSize size(30,30);
            QPixmap widgetImage = m_currentItem->icon(0).pixmap(size);
            drag->setPixmap(widgetImage);
            mimeData->setData("curveData/x-curveData", byteArray);
            drag->setMimeData(mimeData);

            drag->setHotSpot(QPoint(15,15));
            if (!(drag->exec(Qt::MoveAction) == Qt::MoveAction))
            {
//                event->ignore();
                ;
            }
        }

void DataTree::dragEnterEvent(QDragEnterEvent *event)
{
    if (event->mimeData()->hasFormat("curveData/x-curveData"))
    {
        event->acceptProposedAction();
        event->accept();
    }
    else
    {
        event->ignore();
    }
}


void DataTree::dragMoveEvent(QDragMoveEvent *event)
{
    if( event->mimeData()->hasFormat("curveData/x-curveData")){
           event->acceptProposedAction();
           event->accept();
       }
       else
       {
           event->ignore();

       }

}

Accept drop:

void Plot::dropEvent(QDropEvent *event)
{
 if (event->mimeData()->hasFormat("curveData/x-curveData")) {
        QByteArray byteArray = event->mimeData()->data("curveData/x-curveData");
        QDataStream dataStream(&byteArray, QIODevice::ReadOnly);

        QString fileName;
        QString name ;
        QString seq;
        QString type;

        dataStream >> fileName  >> name >> seq >> type;

        emit addCurve(fileName, name, seq, type, this);
        event->acceptProposedAction();
        event->accept();

    } else {
        event->ignore();
    }
}

void Plot::dragEnterEvent(QDragEnterEvent *event)
{
  if ( event->mimeData()->hasFormat("curveData/x-curveData")) {
        event->setDropAction(Qt::MoveAction);
        event->accept();
    } else {
        event->ignore();

    }
}

void Plot::dragMoveEvent(QDragMoveEvent *event)
{

    if (event->mimeData()->hasFormat("curveData/x-curveData")) {
        event->setDropAction(Qt::MoveAction);
        event->accept();
    } else {
        event->ignore();
    }
}

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