[SOLVED] Drag & drop, retrieving a drop signal ?



  • Hey everyone,

    Quite a rough question I am dealing with for 2 days now. I have an application divided in 2 parts. First one is a 3D anatomical human model, second one is a Qt Widget with mini games.

    My objective consists of being able to grab human organs from the left panel (3D model), make them invisible in the model while in drag & drop, put a 2D image as the cursor pixmap, and then drop it on the right panel (Qt).

    If I drop it on the correct widget (a custom DropLabel), the game continues correctly, but if I drop it on a wrong widget (like a normal label or the "return" button for example) I should be able to bring the 3D model of the organ back in visible mode.

    Here is my problem : Everything of what I said above is made, except one thing : I dont find any way to catch an event when dropping the object on a wrong widget. The only thing i figured out would be to remake every class (like a custom QLabel) that accepts drops and from there I could manage to tell my 3D model to update the organ visibility.

    But, this "fix" seems quite wrong to me. What happens if I have like 50 different widgets on the right ? Do I have to make a custom class for EACH ONE of these just for that stupid drag & drop functionnality ? This makes me feel I am doing something wrong, but I have no idea what I have forgotten :/

    Any help on this topic would be much appreciated



  • Hi,

    It would help to see some code but, based on what you said, you should search about "event filtering":http://qt-project.org/doc/qt-5/qobject.html#eventFilter. You can use it to receive events without subclassing objects.


  • Lifetime Qt Champion

    Hi and welcome to devnet,

    If you are using QDrag to accomplish this, you should check the return value of exec, from there you can react accordingly



  • Hello everyone

    Thanks for the answer, that was much appreciated.

    to be honest @tilsitt, I didnt really know which part of the code I could show you cause what I am trying to do seemed quite trivial.

    Anyway, your answer was nice, and I already use this eventFilter for my 3D view, but it happened that it was working on the Qt part (or I did just fail at using it).

    But the answer came from SGaist. I don't know how I failed at looking this return action from QDrag, but as soon as I have seen that exec was a blocking function, I understood that it would give back the resulting drop information (even if I read it carefully, I did not take that in consideration ...)

    So, When my returned action is = to Qt::IgnoreAction, I just re-update my 3D content and show my organ again.

    This works like a charm \o/ Again, thanks guys for the help.


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