IMessageFilter on Python.net

hello.py

import clr
clr.AddReference("System.Windows.Forms")
import System.Windows.Forms as WinForms


class MessageFilter(WinForms.IMessageFilter):
    __namespace__ = 'System.Windows.Forms'

    def PreFilterMessage(self, message):
        print('filter', message)
        return False


class HelloApp(WinForms.Form):
    def __init__(self):
        self.textbox = WinForms.TextBox()
        self.textbox.Text = "Hello World"
        self.Controls.Add(self.textbox)


def main():
    form = HelloApp()
    app = WinForms.Application
    f = MessageFilter()
    app.AddMessageFilter(f)
    app.Run(form)


if __name__ == '__main__':
    main()
    

Here's a minimal demo app for installing a custom IMessageFilter in a Winforms app. If you run this code as presented, the application window displays, but you get a segfault immediately (I presume this is when the first message is passed to the filter).

If you comment out line 25 (installing the actual filter), the code works fine.

If you modify MessageFilter so that it doesn't subclass Winforms.IMessageFilter, you get an error at line 25 saying there's no AddMessageFilter method matching the given arguments.

If you rename or remove the PreFilterMessage() method, you get an error that the Python object doesn't have a PreFilterMessage method.

Any suggestions on what I'm doing wrong, and/or how to fix it?

For those that find this GIST - the problem was identified as pythonnet/pythonnet#965