首先是初始化：

查看Nativeshell的demo代码

// ignore_for_file: undefined_hidden_name, // not in main
import 'package:flutter/material.dart' hide MenuItem;
import 'package:nativeshell/nativeshell.dart';

import 'pages/other_window.dart';
import 'pages/platform_channels.dart';
import 'main_window.dart';
import 'pages/modal_window.dart';
import 'widgets/veil.dart';

void main() async {
  // Disable shader warmup - it delays producing first frame, which we want to
  // produce as soon as possible to reduce time to open new windows.
  disableShaderWarmUp();
  runApp(Main());
}

// Common scaffold code used by each window
class ExamplesWindow extends StatelessWidget {
  const ExamplesWindow({Key? key, required this.child}) : super(key: key);

  final Widget child;

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: DefaultTextStyle(
        style: TextStyle(
          color: Colors.white,
          fontSize: 14,
        ),
        child: WindowLayoutProbe(child: child),
      ),
    );
  }
}

class Main extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Veil(
      child: Container(
        color: Color.fromARGB(255, 30, 30, 35),
        child: WindowWidget(
          onCreateState: (initData) {
            WindowState? state;

            state ??= PlatformChannelsWindowState.fromInitData(initData);
            state ??= ModalWindowState.fromInitData(initData);
            state ??= OtherWindowState.fromInitData(initData);
            state ??= MainWindowState();

            return state;
          },
        ),
      ),
    );
  }
}

这里要注意 ??= 表示 state如果为null则赋值后面的值，否则返回state的自己的值

子窗口：

PlatformChannelsWindowState.fromInitData(initData);
ModalWindowState.fromInitData(initData);
OtherWindowState.fromInitData(initData);

主窗口：
MainWindowState();

其中initData为创建子窗口时传递过来的参数

initData['class'] 这个字段用于标识应该启动哪个子窗口

通过子窗口主动调用子窗口中的方法，并传参

await otherWindow?.callMethod('showMessage', 'Hello from parent window!');

通过父窗口调用父窗口中的方法，并传参

await Window.of(context).parentWindow?.callMethod('showMessage', 'Hello');