How to prevent a LinkBoxGui from accepting an object?

[A Former User]

Hello,
I want my LinkBoxes to refuse an object that is already linked by another LinkBox. How can I do this?

I came up with a simple script demonstrating where I've gotten stuck:

import c4d
from c4d import gui
import c4d.plugins

LINKBOX_GUI_1 = 2001
LINKBOX_GUI_2 = 2002

class LinkBoxDlg(c4d.gui.GeDialog):
    doc = c4d.documents.GetActiveDocument()

    def __init__(self):
        self.linkboxes = list()
        
    def CreateLayout(self):
        if self.GroupBegin(2003, c4d.BFH_SCALEFIT, 1, 2, "", 0, 0):
            self.GroupBorderSpace(10, 10, 10, 10)
            if self.GroupBegin(0, c4d.BFH_SCALEFIT, 2, 1, "", 0, 0):
                self.AddStaticText(2004, c4d.BFH_LEFT, 0, 0, "Object 1")
                link1 = self.AddCustomGui(LINKBOX_GUI_1, c4d.CUSTOMGUI_LINKBOX, "", c4d.BFH_SCALEFIT, 0, 0)
                self.linkboxes.append(link1)
            self.GroupEnd()
            if self.GroupBegin(2005, c4d.BFH_SCALEFIT, 2, 2, "", 0, 0):
                self.AddStaticText(0, c4d.BFH_LEFT, 0, 0, "Object 2")
                link2 = self.AddCustomGui(LINKBOX_GUI_2, c4d.CUSTOMGUI_LINKBOX, "", c4d.BFH_SCALEFIT, 0, 0)
                self.linkboxes.append(link2)
            self.GroupEnd()
        self.GroupEnd()
        return True
    
    def Message (self, msg, result):
        if msg.GetId() == c4d.MSG_DESCRIPTION_CHECKDRAGANDDROP:
            print "*"*50
            print "accept: %s"%msg[c4d.LINKBOX_ACCEPT_MESSAGE_ACCEPT]
            print "control_id: %s"%msg[c4d.LINKBOX_ACCEPT_MESSAGE_CONTROL_ID] # How do I use this control ID to reference the linkbox in the GeDialog?
            print "element: %s"%msg[c4d.LINKBOX_ACCEPT_MESSAGE_ELEMENT] # How do I use this pointer to find the object in the document?
            print "msg_type: %s"%msg[c4d.LINKBOX_ACCEPT_MESSAGE_TYPE]
            print "*"*50
            msg[c4d.LINKBOX_ACCEPT_MESSAGE_ACCEPT] = False # Testing editing the message. Why doesn't this affect the linkbox?
        return gui.GeDialog.Message(self, msg, result)

    def Command(self, id, msg):
        if id == LINKBOX_GUI_1:
            print msg[c4d.BFM_ACTION_VALUE]
        elif id == LINKBOX_GUI_2:
            print msg[c4d.BFM_ACTION_VALUE]
        return True

def main():
    global dlg
    dlg = LinkBoxDlg()
    dlg.Open(c4d.DLG_TYPE_ASYNC, defaultw=300, defaulth=100)

if __name__=='__main__':
    main()

I am not understanding how to use the pointers or how to edit the MSG_DESCRIPTION_CHECKDRAGANDDROP message. Once I know how to get the linkbox's proposed linked object and how to accept/refuse, I can check the other linkboxes' values to determine whether or not to proceed with the object.

Thank you!

[ferdinand]

Hi,

I do not know this for sure, but I would assume that MSG_DESCRIPTION_CHECKDRAGANDDROP is intended - as its name implies - to be used in description resources only. If you check the corresponding message data in C++, you will also see, that it is clearly tied to descriptions. The message being sent does not necessarily mean, that Cinema will also process your response. There is a lot of stuff that only kind of works in GeDialog.

Cheers,
zipit

[PluginStudent]

Why don't you just check the value stored in the gadget in your Command() function (GetLink()) and change it, if it is not OK (SetLink())?

[A Former User]

@PluginStudent Thanks for the idea of how to solve this! I was doing what you described before posting my example, but probably making it too complicated. The documentation for the Link gadget describes the pointer LINKBOX_ACCEPT_MESSAGE_ACCEPT as 'A pointer to a boolean value. Set this value to true to accept the object.' so that sounded like what I needed. I've rewritten the approach you described and have it seemingly working.