在颤动的下拉按钮上显示选定的数据

Question

its actually continuation of my previous question , here i've been successfully populate my list with Json which i retrieved from Get method. as the suggestion, i used futurebuilder widget to build my Dropdownbutton. but my problem is: it cant display any after i picked up the dropdownlist. it crashes.

and i had other thing concerned me. my project is to receive scanned nearby wifi by an esp8266 through http GET method (and later send the password through the apps using POST method). my question is: when im using this Futurebuilder widget, in which "time" that this app actually made http request? does it refresh all the time?

can i just populate the dropdownmenuitem in just one occasion (perhaps in initstate), then asking for refresh only when i needed it (ie using a button). i've been trying to do this but it kept failing.

here's my code

Future<List<Post>> getAllPosts(String url) async {

  final response = await http.get(url);
  return allPostsFromJson(response.body);
}

List<Post> allPostsFromJson(String str) {
  final jsonData = json.decode(str);
  return new List<Post>.from(jsonData.map((x) => Post.fromJson(x)));
}

class Post {
  String name;
  String perc;
  String pass;

  Post({
    this.name,
    this.perc,
    this.pass,
  });

  factory Post.fromJson(Map<String, dynamic> json) => new Post(
        name: json["SSID"],
        perc: json["RSSI"],
        pass: json["PASS"],
      );

  Map<String, dynamic> toJson() => {
        "SSID": name,
        "RSSI": perc,
        "PASS": pass,
      };
}

class LoginPhaseState extends State<LoginPhase>{
  Post selected;

  final String uri = 'http://10.0.2.2/data/connection.json';


  @override
  Widget build(BuildContext context) {
    return FutureBuilder<List<Post>>(
                future: getAllPosts(uri),
                builder: (BuildContext context,
                    AsyncSnapshot<List<Post>> snapshot) {
                  if (!snapshot.hasData) return CircularProgressIndicator();
                  return DropdownButton<Post>(
                    items: snapshot.data
                        .map((ssid) => DropdownMenuItem<Post>(
                              child: Text(ssid.name),
                              value: ssid,
                            ))
                        .toList(),
                    onChanged: (Post value) {
                      setState(() {
                        selected = value;
                      });
                    },
                    isExpanded: false,
                    // value: selected,
                    hint: Text('Select User'),
                  );
                });
  }

} 

Answer 1

try this,

Future<List<Post>> getAllPosts(String url) async {

  final response = await http.get(url);
  return allPostsFromJson(response.body);
}

List<Post> allPostsFromJson(String str) {
  final jsonData = json.decode(str);
  return new List<Post>.from(jsonData.map((x) => Post.fromJson(x)));
}

class Post {
  String name;
  String perc;
  String pass;

  Post({
    this.name,
    this.perc,
    this.pass,
  });

  factory Post.fromJson(Map<String, dynamic> json) => new Post(
        name: json["SSID"],
        perc: json["RSSI"],
        pass: json["PASS"],
      );

  Map<String, dynamic> toJson() => {
        "SSID": name,
        "RSSI": perc,
        "PASS": pass,
      };
}

class LoginPhaseState extends State<LoginPhase>{
  Post selected;

  final String uri = 'http://10.0.2.2/data/connection.json';

  String _selectedChild= "";

  @override
  Widget build(BuildContext context) {
    return FutureBuilder<List<Post>>(
                future: getAllPosts(uri),
                builder: (BuildContext context,
                    AsyncSnapshot<List<Post>> snapshot) {
                  if (!snapshot.hasData)
                   return                                          CircularProgressIndicator();
                  return DropdownButton<Post>(
                    value: _selectedChild == "" ? null : _selectedChild,
                    items: snapshot.data
                        .map((ssid) => DropdownMenuItem<Post>(
                              child: Text(ssid.name),
                              value: ssid,
                            ))
                        .toList(),
                    onChanged: (Post value) {
                      setState(() {
                         _selectedChild = value.name;
                        selected = value;
                      });
                    },
                    isExpanded: false,
                    // value: selected,
                    hint: Text('Select User'),
                  );
                });
  }

}