[Development] QtQuick External Drag Drop Partial Patch -- Help Requested

Rutledge Shawn Shawn.Rutledge at digia.com
Wed Jul 24 10:36:19 CEST 2013

On 23 Jul 2013, at 9:16 PM, Chris Meyer wrote:

> I've been working on adding support for external drag and drop to QtQuick. I've created a patch which addresses the basic needs and have used the resulting capabilities in my non-trivial application to implement drag and drop between a QtQuick view and a widget.
> I'll need help on one particular feature: generating an image of the QtQuick item being dragged. Right now it doesn't use any image -- so dragging works, but the image is just a small gray rectangle.
> In addition, I need feedback on a design choice. I decided to not create a QtQuick MimeData item; but instead add accessor methods directly to DropEvent. This seems reasonable, but a future MimeData object could be re-used if we implement a similar Cut / Copy / Paste functionality. Any thoughts?
> Finally, I'll need some procedural help to make sure the patch is suitable to be added for Qt 5.2 -- specifically to make sure I get examples, tests, and documentation correct.
> Is there someone who has commit access who can help me through this patch?
> Here is the bug report:
> https://bugreports.qt-project.org/browse/QTBUG-27498
> Here is the current code in my patch:
> https://codereview.qt-project.org/61017
> It's not complete, but I'm willing to finish it off (with the help from above). I think this would make a useful addition to Qt 5.2.

Yes I will try to help you because it was on my wish list to try to get DnD done for 5.2 if I could find the time, so now you are saving me some work.  ;-)

For me it's a bit confusing to have both the Drag attached property and the DragEvent; AFAICT they are similar except that Drag is for the source and DragEvent is for the destination, right?  Maybe it could have been the same type of object on both ends.  But since that API is there, we have to keep supporting it anyway, so probably it's good that this patch is going the direction of being similar whether the dragging is being done within the same application or from an external one.

Maybe it would be nice if when receiving a drop, the data being transferred could be handled the same as an ordinary JS object.  Otherwise the reason for all the properties you're adding to QQuickDropEvent is partially to access data from certain keys (text, color, html) and partially to access data of certain types (URLs), right?  It adds convenience for the common use cases.  But DnD implementations are usually supposed to be generic, able to carry data of not-yet-invented types.  And QVariantMap could handle just about anything.  Then when you receive the drop you could iterate the keys, or look for specific keys, and also ask what is the type of each value, depending on how you want to write your application.


I'm not sure about this startExternal function either, because it's procedural rather than declarative.  If you would normally call it whenever your mouse cursor is about to leave the window, maybe we could do that automatically.  Or did you expect to call it in some other context?

Did you write a suitable example yet?  Otherwise maybe I need to write a quickie file manager/viewer or something like that.

I don't know about the drag image yet, but I imagine we can find a way.

Anyway we can continue the discussion on codereview too.

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