How to make DropdownButtonFormField data from sqflite?

class SQLHelper

Future<List<Map<String, dynamic>>> selectAllServer() async {
    final db = await init();
    return db.query('server', orderBy: "ip");
}

class ModalDialog

List<Map<String, dynamic>> _server = [];
void getDataDB() async {
    final data = await db.selectAllServer();
    setState(() {
      _server = data;
    });
}

DropdownButtonFormField(
    onChanged: (val) {},
    items: _server.map((ip) {
        return DropdownMenuItem(
            value: ip['ip'],
            child: Text(ip['ket']),
        );
    }).toList(),
)

Why Value and Child DropdownMenuItem now show? I want to make Dropdown, value and title get from sqflite.