相关疑难解决方法(0)

我想知道在创建数据时,将数据传递给有状态小部件的最佳/最佳性能是什么.

我见过的两种风格是:

class ServerInfo extends StatefulWidget {

  Server _server;

  ServerInfo(Server server) {
    this._server = server;
  }

  @override
    State<StatefulWidget> createState() => new _ServerInfoState(_server);
}

class _ServerInfoState extends State<ServerInfo> {
  Server _server;

  _ServerInfoState(Server server) {
    this._server = server;
  }
}

这种方法保持的值都在ServerInfo和_ServerInfoState,这似乎有点浪费.

另一种方法是使用widget._server:

class ServerInfo extends StatefulWidget {

  Server _server;

  ServerInfo(Server server) {
    this._server = server;
  }

  @override
    State<StatefulWidget> createState() => new _ServerInfoState();
}

class _ServerInfoState extends State<ServerInfo> {
  @override
    Widget build(BuildContext context) {
      widget._server = "10"; …

我试图熟悉颤动，并且遇到了一些奇怪的情况。我想建立一个动态ListView的+按钮可以添加元素的地方。我编写了以下状态代码：

class MyWidgetListState extends State<MyWidgetList> {
  List<Widget> _objectList = <Widget>[
    new Text('test'),
    new Text('test')
  ];

  void _addOne() {
    setState(() {
      _objectList.add(new Text('test'));
    });
  }

  void _removeOne() {
    setState(() {
      _objectList.removeLast();
    });
  }

  @override
  Widget build(BuildContext context) {
    return new Column(
      children: <Widget>[
        new ListView(
          shrinkWrap: true,
          children: _objectList
        ),
        new Row(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            new IconButton(
              icon: new Icon(Icons.remove_circle),
              iconSize: 36.0,
              tooltip: 'Remove',
              onPressed: _objectList.length > 2 ? _removeOne : null,
            ),
            new IconButton(
              icon: …

我想从 a 列表中删除一个项目ListView.builder，但它说它是只读的。

List<Map> entries = [{'date': '2019-08-10', 'data': 85.0}, {'date': '2019-08-14', 'data': 84.0}];

onPressed: () {
  removeItem(index);
}

void removeItem(index) {
  entries.removeAt(index);
}

Another exception was thrown: Unsupported operation: read-only

这也不起作用：

onPressed: () {
  removeItem(date);
}

void removeItem(date) {
  entries.removeWhere((item) => item['date'] == date);
}