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

[Bo Thorsen]

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.

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