wxPython: Threading GUI --> Using Custom Event Handler

Question

I am trying to learn how to run a thread off the main GUI app to do my serial port sending/receiving while keeping my GUI alive. My best Googling attempts have landed me at the

Answer 1

That's the old style of defining custom events. See the migration guide for more information.

Taken from the migration guide:

If you create your own custom event types and EVT_* functions, and you want to be able to use them with the Bind method above then you should change your EVT_* to be an instance of wx.PyEventBinder instead of a function. For example, if you used to have something like this:

myCustomEventType = wxNewEventType()
def EVT_MY_CUSTOM_EVENT(win, id, func):
    win.Connect(id, -1, myCustomEventType, func)

Change it like so:

myCustomEventType = wx.NewEventType()
EVT_MY_CUSTOM_EVENT = wx.PyEventBinder(myCustomEventType, 1)

Here is another post that I made with a couple of example programs that do exactly what you are looking for.

Answer 2

You can define events like this:

from wx.lib.newevent import NewEvent

ResultEvent, EVT_RESULT = NewEvent()

You post the event like this:

wx.PostEvent(handler, ResultEvent(data=data))

Bind it like this:

def OnResult(event):
    event.data

handler.Bind(EVT_RESULT, OnResult)

But if you just need to make a call from a non-main thread in the main thread you can use wx.CallAfter, here is an example.

Custom events are useful when you don't want to hard code who is responsible for what (see the observer design pattern). For example, lets say you have a main window and a couple of child windows. Suppose that some of the child windows need to be refreshed when a certain change occurs in the main window. The main window could directly refresh those child windows in such a case but a more elegant approach would be to define a custom event and have the main window post it to itself (and not bother who needs to react to it). Then the children that need to react to that event can do it them selves by binding to it (and if there is more than one it is important that they call event.Skip() so that all of the bound methods get called).

Answer 3

You may want to use Python threads and queues and not custom events. I have a wxPython program (OpenSTV) that loads large files that caused the gui to freeze during the loading. To prevent the freezing, I dispatch a thread to load the file and use a queue to communicate between the gui and the thread (e.g., to communicate an exception to the GUI).

  def loadBallots(self):
    self.dirtyBallots = Ballots()
    self.dirtyBallots.exceptionQueue = Queue(1)
    loadThread = Thread(target=self.dirtyBallots.loadUnknown, args=(self.filename,))
    loadThread.start()

    # Display a progress dialog
    dlg = wx.ProgressDialog(\
      "Loading ballots",
      "Loading ballots from %s\nNumber of ballots: %d" % 
      (os.path.basename(self.filename), self.dirtyBallots.numBallots),
      parent=self.frame, style = wx.PD_APP_MODAL | wx.PD_ELAPSED_TIME
    )
    while loadThread.isAlive():
      sleep(0.1)
      dlg.Pulse("Loading ballots from %s\nNumber of ballots: %d" %
                (os.path.basename(self.filename), self.dirtyBallots.numBallots))
    dlg.Destroy()

if not self.dirtyBallots.exceptionQueue.empty():
  raise RuntimeError(self.dirtyBallots.exceptionQueue.get())