Hello @cairyn,

Thank you for reaching out to us. I think you are making your life unnecessarily complicated.

PyCapsule is documented but it is documented in the CPython documentation, which I am sure you are aware of since you imported ctypes and were trying to poke around in the data. The type description tells your everything you need to know in the first sentence:

type PyCapsule: This subtype of PyObject represents an opaque value, useful for C extension modules who need to pass an opaque value (as a void* pointer) through Python code to other C code.

You cannot make any use of capsules as they are only a data exchange type for the C layer. Python has only its bindings so that it can act as a glue layer and pass data on. That is what they mean by opaque here. There are some cases where you can hack stuff and write values directly to memory so that the data makes sense for the C/C++ layer or that you can read data from the C++ layer. You will need to know the memory layout of data for that, use a library like struct to en-/decode data, and we will obviously not support this.

So, retrieving a PyCapsule instance is usually the end of the road, as it means that something in the C++ API has not been wrapped. But here you do not really need all the stuff from the message. Just cache the value when a drag and drop occurs and restore the value when something has been written which is not to your liking. Find an example below. I have a hunch that you will consider this 'not what I wan't, since I am sure you could have come up with this yourself. I would suggest embracing Python and not turning this into a technical exercise, as there is only little to win here.

Cheers,
Ferdinand

The result, these three nodes can only be linked in this order, as only the first link box does accept nodes of any type, the second only objects, and the last only objects of type Ocube. Dragging mat onto the last slot will result in the value Cube to remain.
Screenshot 2022-11-28 at 18.55.07.png
The code:

"""Demonstrates how to validate and reject linked nodes in link boxes with a simple data model. Can be run as a Script Manager script. """ import c4d import typing class LinkDialog(c4d.gui.GeDialog): """Provides an example implementation for a set of link boxes in a dialog which only accept certain node types. """ ID_GRP_MAIN: int = 1000 # The IDs of link boxes and their accepted node types as a hashmap. LNK_ITEMS: dict[int, int] = { 1001: c4d.Tbaselist2d, # This link box accepts any node of type BaseList2D 1002: c4d.Obase, # This link box accepts any node of type BaseObject 1003: c4d.Ocube # This link box accepts only nodes of type Ocube } # The settings container used by all link boxes. BC_LNK_SETTINGS: c4d.BaseContainer = c4d.BaseContainer() def __init__(self) -> None: """Initializes the internal cache used to emulate accept events in Python. """ # The link cache organized as (gadget id, value) pairs. self._linkCache: dict[int, c4d.BaseList2D] = {} super().__init__() def CreateLayout(self) -> bool: """ """ self.SetTitle("Link Test") self.GroupBorderSpace(10, 10, 10, 10) if not self.GroupBegin(LinkDialog.ID_GRP_MAIN, c4d.BFH_SCALEFIT, 1): return False # Add the link boxes, I went here not for storing the LinkBoxGui references but retrieving # them when needed later. for gid in LinkDialog.LNK_ITEMS.keys(): gadget: c4d.gui.LinkBoxGui = self.AddCustomGui( gid, c4d.CUSTOMGUI_LINKBOX, "Link", c4d.BFH_SCALEFIT | c4d.BFV_FIT, 10, 10, LinkDialog.BC_LNK_SETTINGS) if not isinstance(gadget, c4d.gui.LinkBoxGui): return False if not self.GroupEnd(): return False return True def _validateLink(self, gid: int) -> bool: """Validates the link box gadget at #gid. When #gid has an illegal value, its cached state will be restored. """ # The linked item is valid, we have nothing to do. node: typing.Optional[c4d.BaseList2D] = self._getLink(gid) if node is not None: return True # It is not, but the cache somehow went out of whack. if gid not in self._linkCache: raise RuntimeError(f"Validation event for uncached parameter value for gid: {gid}") # Restore the previous state. res: bool = self._setLink(gid, self._linkCache[gid]) if res: del(self._linkCache[gid]) return res def _getLink(self, gid: int) -> typing.Optional[c4d.BaseList2D]: """Gets the node value of the link box at #gid. This will use LinkDialog.LNK_ITEMS to determine the type of nodes #gid is supposed to be able to hold. When #gid holds an 'illegal' type, this will return None. """ if gid not in LinkDialog.LNK_ITEMS.keys(): return None gadget: c4d.gui.LinkBoxGui = self.FindCustomGui(gid, c4d.CUSTOMGUI_LINKBOX) if not isinstance(gadget, c4d.gui.LinkBoxGui): raise RuntimeError(f"{gadget = }, {gid = }") # Get the accepted node types from LNK_ITEMS and rely on the type checking of .GetLink. We # could also just retrieve the node without that argument and check ourselves when we want # to do more fancy things like (Obase | Mbase), i.e., accept a BaseObject or a BaseMaterial. typeId: int = LinkDialog.LNK_ITEMS[gid] return gadget.GetLink(c4d.documents.GetActiveDocument(), typeId) def _setLink(self, gid: int, value: c4d.BaseList2D) -> bool: """Sets the node value of the link box at #gid. """ if gid not in LinkDialog.LNK_ITEMS.keys(): return False gadget: c4d.gui.LinkBoxGui = self.FindCustomGui(gid, c4d.CUSTOMGUI_LINKBOX) if not isinstance(gadget, c4d.gui.LinkBoxGui): raise RuntimeError(f"{gadget = }, {gid = }") return gadget.SetLink(value) def Command(self, mid: int, msg: c4d.BaseContainer) -> bool: """Called by Cinema 4D when an action has occurred on one of the gadgets. """ # One of the link boxes has been set, we validate the new state and optionally revert to # the old state. This could also be done with BFM_ACTION in Message(). if mid in LinkDialog.LNK_ITEMS.keys(): self._validateLink(mid) return super().Command(mid, msg) def Message(self, msg: c4d.BaseContainer, result: c4d.BaseContainer) -> int: """Called by Cinema 4D for all GUI events in the dialog. """ # This is a drag and drop event for a link box, we store its current state before the drag # and drop has been carried out. if msg.GetId() == c4d.MSG_DESCRIPTION_CHECKDRAGANDDROP: gid: int = msg.GetLong(c4d.LINKBOX_ACCEPT_MESSAGE_CONTROL_ID) if gid in LinkDialog.LNK_ITEMS.keys(): self._linkCache[gid] = self._getLink(gid) return super().Message(msg, result) if __name__ == "__main__": dlg = LinkDialog() dlg.Open(c4d.DLG_TYPE_ASYNC, defaultw=400, default=200)

SOLVED ColorDialog Flags