Qt Drag and Drop QTreeView

Question

My TreeView has various folder with children. each child has a icon and text-name. the user can select one or more item and drag them into QMDI area. as image for my darg drop i have a local picture drag->setPixmap(QPixmap(myPixImage)). What I need is: how i make the selected item with icon and text as myPixImage dynamically.

Answer 1

It's easy to set the pixmap when your own code create the QDrag object, however using QXxxViews (not only QTreeView) you have only control on the QMimeData (when overriding QAbstractItemModel::mimeData()).

Therefore if you really need that, the only way I now is to subclass QTreeView, overriding (well... reimplenting) mouseMoveEvent() and the like. If you do so, you can get the selected items when creating the QDrag through eg selectionModel()->selectedItems().

Answer 2

First of all: there's no simple way to do this. Basically because QDrag::exec is started when you (as developer) allow the start of the drag (example here ) and it doesn't return until the drag is finished.

You want to change your QDrag object while dragging.

Your best option here is:

1. After creating the Drag object and before running QDrag::exec store the object in some pool that can be accessed anywhere in the code. Probably something like static map<QDrag *> pool
2. Set up a recurrent QTimer event that constantly updates the the QDrag object, which can be obtained from the pool. Do not try using Qthread s as you'll end up with some "QObject can't be moved from/to thread" error.
3. When the drag's ended (as user), clean up the object from the pool

Do mind that you'll have to visually tune the QTimer repeated events accordingly.