Controlling drag&drop using MSG_DESCRIPTION_CHECKDRAGANDDROP

CJtheTiger

Hello coders. Me again.

In a Python ObjectData plugin I added a LINK parameter. I want all BaseObjects except for the plugin object itself to be droppable in here. So I put this in my .res file:

LINK OMYOBJECT_LINK { ACCEPT { Obase; } }

According to the documentation of MSG_DESCRIPTION_CHECKDRAGANDDROP I should listen to this message and if I want the drop to not be acceptable I should return False. So this is in my code:

def Message(self, node: GeListNode, type: int, data: object) -> bool:

    if type == c4d.MSG_DESCRIPTION_CHECKDRAGANDDROP:
        return False

    return True

Just to try it out I always return False. And that's where my issue is: I can still drop any object in there. It is limited to BaseObjects so the ACCEPT { Obase; } seems to work but returning False seems to not prevent the user from dropping something in the link.

What am I doing wrong?

I tried removing ACCEPT { Obase; } from the .res file to no effect.

As an addition: How do I control what the picker of a LINK is allowed to pick? Since it's technically not a drag&drop action it should be something other than MSG_DESCRIPTION_CHECKDRAGANDDROP right?

spedler

In addition to ACCEPT the LINK gui also has a REFUSE statement. You can use that to exclude your plugin ID.

Steve

CJtheTiger

Hello @spedler,

Thanks, this totally works.

However this refuses to take any of my plugin objects, while in the end I only want to refuse the current plugin object; I still want to be able to drag other instances of my plugin object in there.

So in the end I'd still like to solve this using advanced logic in the MSG_DESCRIPTION_CHECKDRAGANDDROP message.

Best regards,
Daniel

m_adam

Hi @CJtheTiger, you were close regarding MSG_DESCRIPTION_CHECKDRAGANDDROP as written in the documentation, you need to set the value of the `resul field of the dictionary like so:


    def Message(self, node: c4d.GeListNode, type: int, data: object) -> bool:

        if type == c4d.MSG_DESCRIPTION_CHECKDRAGANDDROP:
            gadgetId = data["id"]
            dragedObj = data["element"]
            data["result"] = dragedObj != node
            return True
        
        return True

Cheers,
Maxime.

CJtheTiger

Hi @m_adam,

thanks a lot, that did the trick.

To close this topic off here's a snippet to allow other objects but not the current object to be dropped in there:

def Message(self, node: GeListNode, type: int, data: object) -> bool:

    if type == c4d.MSG_DESCRIPTION_CHECKDRAGANDDROP:

        relevant_id = c4d.DescID(c4d.YOUR_PARAM) # Use the ID of the parameter of your object that you want to check.
        current_id: c4d.DescID = data['id']
        
        if relevant_id.IsPartOf(current_id)[0]:        
            dragged_element = data["element"]        
            is_same_object = node == dragged_element        
            data['result'] = not is_same_object        
            return True
        
        return True

Cheers,
Daniel