I’m working on a UI for a system that has agents, which have some qualities, and units, which have multiple agents. I want to be able to display each unit as a list, and drag agents from that list to other units, to reassign them.

There are a lot of examples for using drag and drop with text and files, because WxPython provides drop targets for text and files already. One way that this could be implemented is to serialize the dragged objects to JSON, drop them as text, and then de-serialize them. This has some disadvantages, notably that you end up restricted by what you can pass via JSON. I wanted to pass Python objects, so I used pickle.

What I eventually came up with is below. It uses ObjectListView, which is a great wrapper around WxPython’s ListCtrl. On drag, the selected items of the source list are pickled and passed through the Wx drag and drop mechanism. When they are dropped on another ObjectListView, they are then unpickled and added to that ObjectListView (OLV), and removed from the source OLV.

One thing that this code does leave up to the programmer is ensuring that what goes in on one side of the drag and drop is the same as what is expected out on the other side. Another, slightly more subtle thing, is that this uses pickle on the drop data, so it would be possible to have a script that generates malicious pickle data, and lets you drag it from another UI window to my script’s OLV, whereupon it unpickles into something nasty.

That said, if your attacker is sitting at your computer, launching malicious programs and dragging and dropping stuff out of them, you have already lost, and should probably invest in better door locks.

#!/usr/bin/env python
import wx
import pickle
from ObjectListView import ObjectListView, ColumnDefn #pip install objectlistview
import wx.lib.scrolledpanel as scrolled # UI with a few list boxes that can be drag/dropped between, and have title bars class Agent(object): # Model of a single agent, has: # identifier (string?) # range (km) # speed (kph) # capacity (integer) def __init__(self, ident, range, speed, capacity): self.ident = ident self.range = range self.speed = speed self.capacity = capacity def __repr__(self): return f"<Agent: {self.ident}>" # Drag and drop Drop target that supports receiving pickled # python data structures and doing something with them. class GenericDropTarget(wx.DropTarget): def __init__(self, object): super(GenericDropTarget, self).__init__() self.object = object self.data = wx.CustomDataObject("PickleData") self.SetDataObject(self.data) def OnData(self, x, y, defResult): #print(f"OnData({x},{y})") if self.GetData(): # unpickle data and do something with it pickled_stuff = self.data.GetData() cukes = pickle.loads(pickled_stuff) # TODO We are making the assumption that a "PickleData" # actually only has a list of Agents in it. # Add some checking before making this a real thing, or # limit the type to a more-specific format like "AgentList" self.object.AddObjects(cukes) return defResult def OnDrop(self, x, y): #print(f"OnDrop({x},{y})") return True def OnDragOver(self, x, y, defResult): #print(f"OnDragOver({x},{y})") return defResult def OnEnter(self, x, y, defResult): #print(f"OnEnter({x},{y})") return defResult class UnitPanel(wx.Panel): def __init__(self, parent, unitName="No name set"): wx.Panel.__init__(self, parent=parent, id=wx.ID_ANY) self.dataOlv = ObjectListView(self, wx.ID_ANY, style=wx.LC_REPORT|wx.SUNKEN_BORDER) self.dataOlv.SetColumns([ ColumnDefn("ID", "left", -1, "ident", minimumWidth=100), ColumnDefn("Range", "right", -1, "range", minimumWidth=60), ColumnDefn("Speed", "right", -1, "speed", minimumWidth=60), ColumnDefn("Capacity", "right", -1, "capacity", minimumWidth=60) ]) self.agents = [] self.dataOlv.SetObjects(self.agents) self.dataOlv.Bind(wx.EVT_LIST_BEGIN_DRAG, self.OnDragInit) # Set up a drop target on the listview dt = GenericDropTarget(self.dataOlv) self.dataOlv.SetDropTarget(dt) # Set up a title for this box self.unitLabel = wx.StaticText(self, id=wx.ID_ANY, label=unitName) mainSizer = wx.BoxSizer(wx.VERTICAL) mainSizer.Add(self.unitLabel, proportion=0, flag=wx.ALL, border=5) mainSizer.Add(self.dataOlv, proportion=1, flag=wx.ALL|wx.EXPAND, border=5) self.SetSizer(mainSizer) def populate(self, units): self.agents = [] # for unit in units: # self.agents.append(Agent(unit["ident"], unit["range"], unit["speed"], unit["capacity"])) # self.dataOlv.SetObjects(self.agents) for unit in units: a = Agent(unit["ident"], unit["range"], unit["speed"], unit["capacity"]) self.dataOlv.AddObject(a) #self.draggableURLText.Bind(wx.EVT_MOTION, self.OnStartDrag) def OnDragInit(self, event): # Get all the selected items from this list selected = self.dataOlv.GetSelectedObjects() # Pickle them and put them in a custom data object pickled_selection = pickle.dumps(selected) drag_obj = wx.CustomDataObject("PickleData") drag_obj.SetData(pickled_selection) #Create a drag and drop source from this ObjectListView src = wx.DropSource(self.dataOlv) src.SetData(drag_obj) print("Drag started") result = src.DoDragDrop(wx.Drag_DefaultMove) if result == wx.DragCopy: # We don't copy because agents are hardware self.dataOlv.RemoveObjects(selected) elif result == wx.DragMove: # Remove the data from here, add it to another list self.dataOlv.RemoveObjects(selected) else: # Default, do nothing print("Nothing, nothing, nothing at all") class AssetFrame(wx.Frame): def __init__(self): wx.Frame.__init__(self, parent=None, id=wx.ID_ANY, title="ObjectListView Demo", size=(800, 600)) self.panel = scrolled.ScrolledPanel(self, id=wx.ID_ANY) self.mainSizer = wx.BoxSizer(wx.VERTICAL) self.panel.SetSizer(self.mainSizer) self.panel.SetupScrolling() self.Show() def populate(self, config): for unit in config["units"]: unit_panel = UnitPanel(self.panel, unitName=unit["name"]) unit_panel.populate(unit["agents"]) self.mainSizer.Add(unit_panel) if __name__ == "__main__": app = wx.App(False) # We're going to need to be able to populate the frame from the config, # so represent the data as a data structure and initialze with that config = {"units": [{"name": "Unimatrix 01", "agents": [ {"ident": "7 of 9", "range": 10, "speed": 10, "capacity": 12}, {"ident": "Third of 5", "range": 10, "speed": 10, "capacity": 12} ]}, {"name": "Unit 2", "agents": [ {"ident": "u2s1", "range": 10, "speed": 10, "capacity": 12}, {"ident": "u2a2", "range": 10, "speed": 10, "capacity": 12}, {"ident": "u2a3", "range": 10, "speed": 10, "capacity": 12} ]}, {"name": "Unit Foo", "agents": [ {"ident": "bar", "range": 10, "speed": 10, "capacity": 12}, {"ident": "baz", "range": 10, "speed": 10, "capacity": 12}, {"ident": "quux", "range": 10, "speed": 10, "capacity": 12} ]}, {"name": "Enterprise", "agents": [ {"ident": "Galileo", "range": 10, "speed": 10, "capacity": 12}, {"ident": "Copernicus", "range": 10, "speed": 10, "capacity": 12} ]}, {"name": "GSV Insufficent Gravitas", "agents": [ {"ident": "GCU Nervous Energy", "range": 1000000, "speed": 3452334, "capacity": 13452342}, {"ident": "GCU Grey Area", "range": 1000000, "speed": 234523546, "capacity": 234562312} ]}] } frame = AssetFrame() frame.populate(config) app.MainLoop()

I called the unpickled data “cukes” because this is demo code, and I was being silly. A cucumber is, after all, what you get when you undo the process of making pickles. You may want to change that if you copy/paste this into production code.