ScreenListener support for macos and windows

[holotrek]

Are ScreenListener events supported on macos and windows? Looking at the code, it seems that the only version that emits events is Linux when displays are added/removed in the following lines:

screen_retriever/linux/screen_retriever_plugin.cc

Line 192 in 4f3831a

g_signal_connect_object(display, "monitor-added",

screen_retriever/linux/screen_retriever_plugin.cc

Line 195 in 4f3831a

g_signal_connect_object(display, "monitor-removed",

I would like to have that ability on the other systems, but don't have the knowledge enough to know how to modify your code to do so.

As a side note, there's also no documentation on the README going over the event and whether it is supported on different systems.

[holotrek]

I have gotten this working with MacOS. If you are running on mac and want to detect when the screen changes, update your pubspec.yml to:

  screen_retriever:
    git:
      url: https://github.com/holotrek/screen_retriever
      ref: "ad04fd32637ac901e1d64d0725ac6343a0347255"

Then mark a widget as inheriting ScreenListener and add an event that can update your display list, i.e.:

class MyDisplaysState extends State<MyDisplays> with ScreenListener {
  @override
  void initState() {
    super.initState();
    screenRetriever.addListener(this);
  }

  @override
  void onScreenEvent(String eventName) {
    // eventName may be "monitor-added" or "monitor-removed"
    super.onScreenEvent(eventName);
    setState(() {});
  }

  @override
  void dispose() {
    screenRetriever.removeListener(this);
    super.dispose();
  }
}

I'll post back with an updated ref if I get this working with Windows and also will submit a PR.