[Interest] Getting QTreeView item click offset for DnD

[Jason H]

There is no drag start event.

I attempted to copy what they did in an example: 
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); } }

However this wont work because I am using a QTreeView which uses item delegates. So the following won't work:
QLabel *child = static_cast<QLabel*>(childAt(event->pos()));
drag->setHotSpot(event->pos() - child->pos())

Because QTreeView uses delegates. I need some way to find out where in the delegate the mouse was clicked.

________________________________
From: Bill Crocker <william.crocker at analog.com>
To: 
Cc: "interest at qt-project.org" <interest at qt-project.org> 
Sent: Wednesday, April 18, 2012 10:46 AM
Subject: Re: [Interest] Getting QTreeView item click offset for DnD

On 04/18/2012 10:33 AM, Jason H wrote:
> That is wrong, because that is the mouse position of the drop location.
>
> Here, let me make a picture
> +--------------+
> |---deleg.te---|
> +--------------+
>
> Now the "." in the delegate is the mouse location. When I drop this delegate on
> the widget, I get the location of the "." in the widget coordinates. The problem
> is, if I put an item at that location it is off by
> +--------
> |---deleg
>
> So I need to subtract (10,2 - in characters) from the "." position(10,2) to get
> the proper place in the widget to position the item. This is the offset I am
> looking for.
>

Perhaps you need to take control of the Drag-Start event and
there-by take control of the creation of the dragged image relative
to the Drag-Start pos().

Perhaps the information you seek is buried in the mime data
provided as part of the drop event.

>
>
> --------------------------------------------------------------------------------
> *From:* Bill Crocker <william.crocker at analog.com>
> *To:* interest at qt-project.org
> *Sent:* Wednesday, April 18, 2012 10:17 AM
> *Subject:* Re: [Interest] Getting QTreeView item click offset for DnD
>
> On 04/18/2012 10:07 AM, Jason H wrote:
>>  Please, any help?
>>
>>  I'm stuck.
>>
>
> How about this:
>
> const QPoint & QDropEvent::pos () const
>
> Returns the position where the drop was made.
>
>
>>  --------------------------------------------------------------------------------
>>  *From:* Jason H <scorp1us at yahoo.com <mailto:scorp1us at yahoo.com>>
>>  *To:* André Somers <andre at familiesomers.nl <mailto:andre at familiesomers.nl>>;
> "interest at qt-project.org <mailto:interest at qt-project.org>"
>>  <interest at qt-project.org <mailto:interest at qt-project.org>>
>>  *Sent:* Tuesday, April 17, 2012 11:09 AM
>>  *Subject:* Re: [Interest] Getting QTreeView item click offset for DnD
>>
>>  Yes. However nothing gives me the click coordinates.
>>
>>  I am dragging an item to a subclassed QLabel. When the drop occurs, the top-left
>>  of the item is placed at the mouse cursor. This is wrong. The item should be
>>  placed at wherever Qt drew it last, which is offset by the mouse coords in the
>>  item.
>>
>>
>>  --------------------------------------------------------------------------------
>>  *From:* André Somers <andre at familiesomers.nl <mailto:andre at familiesomers.nl>>
>>  *To:* "interest at qt-project.org <mailto:interest at qt-project.org>"
> <interest at qt-project.org <mailto:interest at qt-project.org>>
>>  *Sent:* Tuesday, April 17, 2012 11:00 AM
>>  *Subject:* Re: [Interest] Getting QTreeView item click offset for DnD
>>
>>  Op 17-4-2012 16:54, Jason H schreef:
>> > Well I am confused about how the view works.
>> > I'm using QStandardItems, so whatever Qt does with those... I can't find
>> > documentation anywhere...
>> >
>>  The items in the model do not become widgets. That would be very inefficient.
>>  Instead, they are rendered in the view using a delegate that has been set on
>>  your view. By default, that is a QStyledItemDelegate.
>>
>>  Anyway, for D&D purposes, an item is just a package of data. At the moment you
>>  have the model index, you have access to the data of the item.
>>
>>  Perhaps the question should be: why are you reimplementing the mousePressEvent
>>  in this context at all? Did you study the "Using Drag and Drop with Item Views"
>>  topic from the Model/View Programming documentation page?
>>
>>  André
>>
>>
>> >
>> > --------------------------------------------------------------------------------
>> > *From:* André Somers <andre at familiesomers.nl <mailto:andre at familiesomers.nl>>
> <mailto:andre at familiesomers.nl <mailto:andre at familiesomers.nl>>
>> > *To:* interest at qt-project.org <mailto:interest at qt-project.org>
> <mailto:interest at qt-project.org <mailto:interest at qt-project.org>>
>> > *Sent:* Tuesday, April 17, 2012 10:40 AM
>> > *Subject:* Re: [Interest] Getting QTreeView item click offset for DnD
>> >
>> > Op 17-4-2012 16:35, Jason H schreef:
>> >> I need to repeat this. I'm still lost.
>> >> here is my code (child is always NULL):
>> >> voidDataPointTreeView::mousePressEvent(QMouseEvent*event)
>> >> {
>> >> QTreeView::mousePressEvent(event);
>> >> QModelIndex mi = indexAt(event->pos());
>> >> QWidget *child = indexWidget(mi);
>> >> //QWidget *child = static_cast<QWidget*>(childAt(event->pos()));
>> >> if (!child)
>> >> return;
>> >>
>> >> m_dragOffset = event->pos() - child->pos();
>> >> }
>> >>
>> > Are you even using widgets for your items? I mean: do you call setIndexWidget
>> > anywhere? If not, perhaps you should check what indexWidget() actually returns?
>>
>>
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