将数据添加到另一个页面上的列表 Flutter

Question

我在这样的有状态小部件中有一个事件名称列表

main.dart

class Fav extends StatefulWidget {
  @override
  _FavState createState() => _FavState();
}

class _FavState extends State<Fav> {
  final PageController ctrl = PageController(viewportFraction: 0.8);

  final Firestore db = Firestore.instance;
  Stream slides;

  var fav = ['3-Tech Event']; 
. 
.
.

在另一个页面上，我想添加一个字符串，比如说，

'5-Art Exhibit'

进入

var fav = ['3-Tech Event'];

得到最终结果

fav = ['3-Tech Event', '5-Art Exhibit'];

在上面的页面上。我怎么做？这是我的按钮代码

Event.dart

class Star extends StatefulWidget {
      @override
      _StarState createState() => _StarState();
    }

    class _StarState extends State<Star> {
      Color _iconColor = Colors.grey;

      @override
      Widget build(BuildContext context) {
        return Container(
              padding: EdgeInsets.all(55.0),
              child: Transform.scale(
                scale: 2.0,
                  child: IconButton(
                      icon: Icon(
                        Icons.star,
                        color: _iconColor,
                      ),
                      onPressed: () {
                        setState(() {
                          _iconColor = (_iconColor == Colors.yellow) ?  Colors.grey : Colors.yellow;

                        });
                      })
              ),
        );
      }
    }

提前谢谢你！

更新

我遵循@Viren V Varasadiya 的建议并将我的代码更新到此

main.dart

class Fav extends StatefulWidget {

  @override
  _FavState createState() => _FavState();
}

class _FavState extends State<Fav> {

  var fav = ['3-Tech Event'];
  updatedata(String item) {
    setState(() {
      fav.add(item);
    });
  }

在另一个文件上，我删除了 Star 类（因为它本来打算在另一个类中使用），它看起来像这样

class Event extends StatefulWidget {
  final eventInfo;
  Event({Key key, List eventInfo})    //I have to pass a list of data to this 
      : this.eventInfo = eventInfo,   //page from another class
        super(key: key);

  final Function updatedata;
  Event.addToFavWith({this.updatedata});

  @override
  _EventState createState() => _EventState();
}

class _EventState extends State<Event> {
  Color _iconColor = Colors.grey;

  @override
  Widget build(BuildContext context) {
.
.
.
Container(                          //This used to be Container(child:Star())
          child: InkWell(
        child: Container(
          padding: EdgeInsets.all(55.0),
          child: Transform.scale(
              scale: 2.0,
              child: IconButton(
                  icon: Icon(
                    Icons.star,
                    color: _iconColor,
                  ),
                  onPressed: () {
                    setState(() {
                      _iconColor = (_iconColor == Colors.yellow)
                          ? Colors.grey
                          : Colors.yellow;
                      widget.updatedata(name);
                    });
                  })),
        ),
      )),

现在我遇到了一些错误。

所有最终变量都必须初始化，但 'eventInfo' 不是。尝试 为该字段添加一个初始化器。

所有最终变量都必须初始化，但“updatedata”不是。尝试 为该字段添加一个初始化程序。

Answer 1

您必须在父小部件中创建一个函数并将其传递给子小部件并在子小部件中调用它，我们为您工作。

遵循最少的代码可以帮助您更多。

class DeleteWidget extends StatefulWidget {
  @override
  _DeleteWidgetState createState() => _DeleteWidgetState();
}

class _DeleteWidgetState extends State<DeleteWidget> {
  var fav = ['3-Tech Event'];

  updatedata(String item) {
    setState(() {
      fav.add(item);
    });
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
        body: Container(
            child: Column(
      mainAxisAlignment: MainAxisAlignment.center,
      children: [
        Text(fav.toString()),
        Star(
          updatedata: updatedata,
        ),
      ],
    )));
  }
}

class Star extends StatefulWidget {
  final Function updatedata;
  Star({this.updatedata});
  @override
  _StarState createState() => _StarState();
}

class _StarState extends State<Star> {
  @override
  Widget build(BuildContext context) {
    return Container(
      child: RaisedButton(
          child: Text("add item"),
          onPressed: () {
            widget.updatedata('5-Art Exhibit');
          }),
    );
  }
}

更新：

不需要创建命名构造函数。

class Event extends StatefulWidget {
  final eventInfo;
  Event({Key key, List eventInfo, this.updatedata})    //I have to pass a list of data to this 
      : this.eventInfo = eventInfo,   //page from another class
        super(key: key);

  final Function updatedata;

  @override
  _EventState createState() => _EventState();
}