小编wil*_*aya的帖子

如何将列表编码为json？

这是我给杰森的课。

class Players{
  List<Player> players;

  Players({this.players});

  factory Players.fromJson(List<dynamic> parsedJson){

    List<Player> players = List<Player>();
    players = parsedJson.map((i)=>Player.fromJson(i)).toList();

    return Players(
      players: players,
    );
  }
}

class Player{
  final String name;
  final String imagePath;
  final int totalGames;
  final int points;

  Player({this.name,this.imagePath, this.totalGames, this.points});

  factory Player.fromJson(Map<String, dynamic> json){

    return Player(
      name: json['name'],
      imagePath: json['imagePath'],
      totalGames: json['totalGames'],
      points: json['points'],
    );
  }
}

我设法用fromJson解码，结果在List中。现在，我有另一个播放器要添加json并想将列表编码为json，现在不知道要这样做了。结果总是失败。

var json = jsonDecode(data);
List<Player> players = Players.fromJson(json).players;
Player newPlayer = Player(name: _textEditing.text,imagePath: _imagePath,totalGames: 0,points: 0);
players.add(newPlayer);
String encode = jsonEncode(players.players); …

如何更改 PopupMenuButton 上的图标颜色，我已将主题与 iconTheme 一起使用，但它不会影响 CheckedPopupMenuItem 或 PopupMenuItem 上的图标。

Scaffold(
      backgroundColor: Colors.transparent,
      appBar: AppBar(
        elevation: 0.0,
        backgroundColor: Colors.transparent,
        actions: <Widget>[
          Theme(
            data: Theme.of(context).copyWith(
              cardColor: Colors.indigo,
              iconTheme: IconThemeData(color: Colors.white),
            ),
            child: ListTileTheme(
              iconColor: Colors.white,
              child: PopupMenuButton<String>(
                onSelected: _showCheckedMenuSelections,
                itemBuilder: (BuildContext context) => <PopupMenuEntry<String>>[
                  CheckedPopupMenuItem<String>(
                    value: _checkedValue1,
                    checked: _showRoles,
                    child: Text(_checkedValue1, style: Theme.of(context).textTheme.body1),
                  ),
                  const PopupMenuDivider(),
                  PopupMenuItem<String>(
                    value: 'Get Link',
                    child: ListTile(
                      leading: Icon(Icons.phonelink),
                      title: Text('Get link', style: Theme.of(context).textTheme.body1),
                    ),
                  ),
                ],
              ),
            ),
          ),
        ],
      ),

结果是这样的：

为什么Kotlin中有这样的emptyList构造函数？它是一个不可变的List,所以没有办法添加或删除它的元素,它是空的!那么,这个emptyList的功能是什么？

新来的颤振。我知道如何设置警报对话框的状态，但是由于需要点击 ()=> _createPlayer 之类的功能，它不想重建警报对话框。我想知道如何在需要点击警报对话框时设置状态。

 File _image;

    GestureDetector(
                onTap: () => _createPlayer(),

点击后，它将显示一个警告对话框，如下所示：

_createPlayer() {
    return showDialog(
        context: context,
        builder: (BuildContext context) {
          return AlertDialog(
            shape: RoundedRectangleBorder(
                borderRadius: BorderRadius.all(Radius.circular(32.0))),
            content: Container(
              height: 400,
              width: 300,
              child: Column(
                children: <Widget>[
                  Text('Create Player', style: Theme
                      .of(context)
                      .textTheme
                      .body1),
                  GestureDetector(
                    onTap: _getImageCamera,
                    child: CircleAvatar(
                      radius: 100,
                      backgroundColor: Colors.white,
                      backgroundImage: _image != null ? FileImage(_image) : AssetImage('assets/images/undercover.png'),
                    ),
                  ),
                ],
              ),
            ),
          );
        });
  }

_getImageCamera() async{
    var image = await ImagePicker.pickImage(source: ImageSource.camera);

    setState(() { …