[Qt-interest] Drag and Drop when source is deleted

[Martin Grossberger]

> Den 20-05-2011 11:48, Martin Grossberger skrev:
>>> Den 20-05-2011 11:40, Martin Grossberger skrev:
>>>>> Hi
>>>>>
>>>>> Am 20.05.2011 11:04, schrieb Martin Grossberger:
>>>>>> However, the program still crashes before I can even check if the
>>>>>> widget
>>>>>> still exists on dropping.
>>>>> Maybe it's not what you are dragin, but the drag object itself. Is it
>>>>> created on the heap or is there a possibility that it gets 
>>>>> destroyed if
>>>>> the corresponding widget gets deleted while you are dragging?
>>>>>
>>>>> Alex
>>>>> _______________________________________________
>>>>> Qt-interest mailing list
>>>>> Qt-interest at qt.nokia.com
>>>>> http://lists.qt.nokia.com/mailman/listinfo/qt-interest
>>>> Hi,
>>>>
>>>> It is created on the heap. I've hacked together a minimalistic program
>>>> to reproduce the issue, and it has the same issue.
>>>> To reproduce the issue:
>>>>
>>>> 1. Compile the code attached
>>>> 2. Start dragging the DragWidget and hold it for 5 seconds
>>>> 3. After those 5 seconds the DragWidget gets deleted, if you drop
>>>> now, the program will crash
>>>
>>> That's because you have created the drag object with the widget as
>>> QObject parent. So when the widget is deleted, so is the drag object.
>>>
>>> Don't do that :)
>>>
>>> Bo Thorsen,
>>> Fionia Software.
>>>
>> Can you send me a line of code how this should work?
>> If I change the creation of the drag to:
>> QDrag *drag = new QDrag(0);
>> then no drag is actually happening.
>
> Sorry, that was the wrong direction. Apparently, you need to make sure 
> the widget is alive for as long as the drag is active. I didn't know 
> this. And it's IMO a Qt bug not to allow the drag source to be deleted.
>
> Bo Thorsen,
> Fionia Software.
>
I was hoping there would be another solution, because I have found no 
way to tell if a drag&drop operation is occuring.
If I understand the documentation correctly, the best approach would be 
to hide the widget instead of deleting it, and delete it once the 
drag&drop operation is done (in mouseMoveEvent? according to the docs 
QDrag::start or exec blocks the event loop).

Your help is much appreciated.

Kind Regards,
Martin Grossberger
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