https://plugincafe.maxon.net/topic/11993/treeview-c4d-dragtype_files/7

testplugin.pyp

import c4d
from c4d import gui
from c4d import plugins

from os import path

PLUGIN_ID = 1000001 # Test plugin id


class ListItem:
    """
    class ListItem:
    A simple class for storing a single string
    Implements equality operator to be able to easily compare with Filename string BEFORE instantiation,
    see InsertObject()
    """

    def __init__(self, filename):
        self.__filename = filename  # The simple String/Filename

    @property
    def filename(self):
        return self.__filename

    def __eq__(self, other):
        return self.__filename == other  # compares the Filename/String of an instance with a given Filename/String


class Tvf(gui.TreeViewFunctions):
    def GetFirst(self, root, userdata):  # Bare minimum, neccessary to insert ListItems
        if not root:
            return None
        return root[0]

    def GetNext(self, root, userdata, obj):  # Bare minimum, neccessary to insert ListItems
        """
        Get next or None
        Args:
            root (list): The list
            obj (ListItem): The ListItem to get the next element from the list

        Returns: None or next ListItem

        """
        if not root:
            return None

        next_idx = root.index(obj) + 1
        return root[next_idx] if next_idx < len(root) else None

    def AcceptDragObject(self, root, userdata, obj, dragtype, dragobject):
        """
        Checks if the dragged object is allowed.
        Returns NOTOK, to prevent Cinema 4Ds default action when dragobject is not accepted
        """
        if dragtype == c4d.DRAGTYPE_FILENAME_OTHER:
            return c4d.INSERT_AFTER, False

        return c4d.NOTOK, False

    def InsertObject(self, root, userdata, obj, dragtype, dragobject, insertmode, bCopy):
        """
        Creates a ListItem and initializes filename property, then adds it to the list (root)
        """
        root.append(ListItem(dragobject))


    def GetName(self, root, userdata, obj):
        return obj.filename


class TestDialog(gui.GeDialog):
    IDD_TREEVIEW = 10000
    TV_FILENAME = 11001

    def __init__(self, items):
        self.__items = items  # Hold ref to the Filename List
        self.__treegui = None  # the TreeViewCustomGui
        self.__tv = Tvf()  # instantiate TreeViewFunctions

    def CreateLayout(self):
        settings = c4d.BaseContainer()
        settings.SetBool(c4d.TREEVIEW_OUTSIDE_DROP, True)  # Allows dragging files from outside Cinema 4D
        settings.SetBool(c4d.TREEVIEW_HAS_HEADER, True)

        self.__treegui = self.AddCustomGui(self.IDD_TREEVIEW, c4d.CUSTOMGUI_TREEVIEW, "",
                                           c4d.BFH_SCALEFIT | c4d.BFV_SCALEFIT,
                                           300,
                                           300,
                                           settings)

        return True

    def InitValues(self):
        layout_bc = c4d.BaseContainer()
        layout_bc.SetLong(self.TV_FILENAME, c4d.LV_TREE)
        self.__treegui.SetLayout(1, layout_bc)

        self.__treegui.SetHeaderText(self.TV_FILENAME, "Filename")
        self.__treegui.Refresh()

        self.__treegui.SetRoot(self.__items, self.__tv, None)
        return True


class TestCommand(plugins.CommandData):
    def __init__(self):
        self.__dlg = None
        self.__items = list()

    def Register(self):
        return plugins.RegisterCommandPlugin(PLUGIN_ID, "Test-Plugin", 0, None, None, self)

    def Execute(self, doc):
        if self.__dlg is None:
            self.__dlg = TestDialog(self.__items)

        return self.__dlg.Open(dlgtype=c4d.DLG_TYPE_ASYNC, pluginid=PLUGIN_ID, defaulth=400, defaultw=400)

    def RestoreLayout(self, sec_ref):
        if self.__dlg is None:
            self.__dlg = TestDialog(self.__items)

        return self.__dlg.Restore(pluginid=PLUGIN_ID, secret=sec_ref)


if __name__ == '__main__':
    TestCommand().Register()