Dart/Flutter中按钮的OnPressed事件点了没反应，怎么回事？

Dart Flutter

Widget createBottomSheetDialog(){
  var _ipAddress = 'Unknown';
  print("abc");

  void _getIPAddress() async {
    var url = 'https://httpbin.org/ip';
    var httpClient = new HttpClient();

// 实际运行后点击按钮，根本不会打印如下2行日志，好像压根没运行到这里
    print(url);
    print("123");

    String result;
    try {
      var request = await httpClient.getUrl(Uri.parse(url));
      var response = await request.close();
      if (response.statusCode == HttpStatus.OK) {
        var json = await response.transform(utf8.decoder).join();
        var data = jsonDecode(json);
        result = data['origin'];

      } else {
        result =
        'Error getting IP address:\nHttp status ${response.statusCode}';
      }
    } catch (exception) {
      result = 'Failed getting IP address';
    }

    setState() {
      _ipAddress = result;
    }
    print(result);
  }

  var btn = IconButton(
    onPressed: _getIPAddress,
    tooltip: 'Get IP',
    icon: Icon(Icons.cake),
  ); // This trailing comma makes auto-formatting nicer for build methods.

  return new Container(
    color: Colors.blue,
    child: new Column(
      mainAxisSize: MainAxisSize.min,
      crossAxisAlignment: CrossAxisAlignment.stretch,//填满交叉轴
      children: <Widget>[
        new Text(_ipAddress),
        new Text("111111111111111111111111111111"),
        btn,
      ],
    ),
  );
}