Easiest way to add 3 dot pop up menu AppBar in Flutter

The simplistic way is undoubtedly to avoid auxiliary classes.
As of Dart 2.2 with the use of set literals, we can place the map of menu items in the app bar directly

 appBar: AppBar(
        title: Text('Homepage'),
        actions: <Widget>[
          PopupMenuButton<String>(
            onSelected: handleClick,
            itemBuilder: (BuildContext context) {
              return {'Logout', 'Settings'}.map((String choice) {
                return PopupMenuItem<String>(
                  value: choice,
                  child: Text(choice),
                );
              }).toList();
            },
          ),
        ],
      ),

and handle click with value of Item text in method

void handleClick(String value) {
    switch (value) {
      case 'Logout':
        break;
      case 'Settings':
        break;
    }
}