DragDrop Color

I am creating a custom color picker by sub classing QFrame. There are three main functionality I would be needing.

1. A color picker
2. dragdrop color to other picker
3. right click menu

There won't be any problem in 1 and 3. How ever for 2 there are:

When you drop color to target, a menu appears with two options: swap & replace
If user select "swap", it should swap the colors of source and target
If user select "replace", it should replace the color of target with source.

drag & drop is having some problem:

Code:

---

void DragWidget::dragEnterEvent(QDragEnterEvent *event)
{
    if (event->mimeData()->hasColor()) {
        if (event->source() == this) {
            event->setDropAction(Qt::MoveAction);
            event->accept();
        }
        else {
            event->acceptProposedAction();
        }
    }
    else {
        event->ignore();
    }
 }
 
void DragWidget::dragMoveEvent(QDragMoveEvent *event)
{
    if (event->mimeData()->hasColor()) {
        if (event->source() == this) {
            event->setDropAction(Qt::MoveAction);
            event->accept();
        }
        else {
            event->acceptProposedAction();
        }
    }
    else {
        event->ignore();
    }
 
}
 
void DragWidget::dropEvent(QDropEvent *event)
{
    if (event->mimeData()->hasColor()) {
        myColor = qvariant_cast<QColor>(event->mimeData()->colorData());
 
        if (event->source() == this) {
            event->setDropAction(Qt::MoveAction);
            event->accept();
        } else {
            event->acceptProposedAction();
        }
    } else {
        event->ignore();
    }
}
 
 
void DragWidget::mousePressEvent(QMouseEvent *event)
{
    QMimeData *mimeData = new QMimeData;
    mimeData->setColorData(QVariant(myColor));
 
    QDrag *drag = new QDrag(this);
    drag->setMimeData(mimeData);
}

---

What problem is the drag & drop having?

http://catb.org/~esr/faqs/smart-questions.html

Nothing is happening.

Too bad.

http://catb.org/~esr/faqs/smart-questions.html

Got it.....

in "mousePressEvent" I have to add this:

Code:

---

Qt::DropAction dropAction = drag->exec(Qt::CopyAction,Qt::CopyAction);

---

Good for you.
http://catb.org/~esr/faqs/smart-questions.html

It seems there is something wrong here and it's creating another problem.

Code:

---

void DragWidget::mousePressEvent(QMouseEvent *event)
{
 
    // Pack mime data
    QMimeData *mimeData = new QMimeData;
    mimeData->setColorData(QVariant(myColor));
 
    // Prepare cursor image
    QPixmap pixmap(this->size());
    QPainter painter;
    painter.begin(&pixmap);
    painter.fillRect(pixmap.rect(), myColor);
    painter.end();
 
    // We establish QDrag object, draw cursor and embed data
    QDrag *drag = new QDrag(this);
    drag->setMimeData(mimeData);
    drag->setPixmap(pixmap);
    drag->setHotSpot(event->pos());
 
    sourcePicker = drag->source();
 
    // We send it
   drag->exec(Qt::CopyAction);
 
 
}
 
void DragWidget::mouseReleaseEvent(QMouseEvent *event)
{
 
    if (event->type() == QEvent::MouseButtonRelease){
        QColor color = QColorDialog::getColor(QColor(myColor), this);
         if (color.isValid()) {
             setPalette(QPalette(color));
             setAutoFillBackground(true);
             myColor = color;
         }
     }
    else
        event->ignore();
}

---

With this line in "mousePressEvent":

Code:

---

drag->exec(Qt::CopyAction);

---

drag n drop is working fine but "mouseReleaseEvent" is not getting called. If I comment this
line "releaseEvent" is getting called.

Secondly, I have to add the functionality to make this widget as color picker also, I added color picking dialog in "releaseEvent". This won't work as expected because the "dropping"
event is actually a "releaseEvent" and as you drop on target picker dialog shows up.

A hack to this problem is to show color dialog when there is "down" and "up" on same widget. Using a bool var, you set state true, when there is a mouse down and in mouse up
event, check the state of this var, if it's true, show color dialog and set it again to false.
Am I right here or there is a better way of doing this?

How do I setup a menu, which appears at dropping? "swap color" or "replace color"

Prashant

What's the point of checking the event type in mouseReleaseEvent()?

Drop event is a drop event and not mouse release event. Here is an extract from my QwwTwoColorIndicator:

Code:

---

void QwwTwoColorIndicator::mouseMoveEvent(QMouseEvent *ev) {
    Q_D(QwwTwoColorIndicator);
    if (d->fgP || d->bgP) {
        if (dragEnabled() && (ev->pos() - d->pressPos).manhattanLength() >= QApplication::startDragDistance()) {
            QColor col = d->fgP ? fgColor() : bgColor();
            ColorDrag *drag = new ColorDrag(this, col, col.name());
            drag->exec();
            d->fgP = d->bgP = false;
            update();
        }
    } else if (testAttribute(Qt::WA_Hover)) update();
    QWidget::mouseMoveEvent(ev);
}

---

Code:

---

void QwwTwoColorIndicator::mouseReleaseEvent(QMouseEvent *ev) {
    Q_D(QwwTwoColorIndicator);
    if (ev->button() == Qt::LeftButton) {
        if (d->fgP && d->foregroundRect().contains(ev->pos())) {
            emit fgClicked();
            if (d->active) {
#if QT_VERSION >= 0x040500
                QColor c = QColorDialog::getColor(d->fg, this, tr("Choose foreground color"), QColorDialog::ShowAlphaChannel);
#else
                QColor c = QColorDialog::getColor(d->fg, this);
#endif
                if (c.isValid()) {
                    setFgColor(c);
                }
            }
        } else if (d->bgP && d->backgroundRect().contains(ev->pos())) {
            emit bgClicked();
            if (d->active) {
#if QT_VERSION >= 0x040500
                QColor c = QColorDialog::getColor(d->bg, this, tr("Choose background color"), QColorDialog::ShowAlphaChannel);
#else
                QColor c = QColorDialog::getColor(d->bg, this);
#endif
                if (c.isValid()) {
                    setBgColor(c);
                }
            }
        }
        d->fgP = d->bgP = false;
        update();
    }
}

---

Code:

---

void QwwTwoColorIndicator::dropEvent(QDropEvent *ev) {
    Q_D(QwwTwoColorIndicator);
    QColor col;
    if (ev->mimeData()->hasColor())
        col = qvariant_cast<QColor>(ev->mimeData()->colorData());
    else
        col.setNamedColor(ev->mimeData()->text());
    if (d->foregroundRect().contains(ev->pos())) {
        setFgColor(col);
    } else if (d->backgroundRect().contains(ev->pos())) {
        setBgColor(col);
    }
    ev->setDropAction(Qt::CopyAction);
}

---

There is also dragEnterEvent and dragMoveEvent implemented.