flutter - Flutter:在其他有状态的小部件中更新字符串

Question

我正在使用全状态窗口小部件来处理文本的长度。 (显示更多，显示更少)

class DescriptionTextWidget extends StatefulWidget {
  final String text;

  DescriptionTextWidget({@required this.text});

  @override
  _DescriptionTextWidgetState createState() =>
      new _DescriptionTextWidgetState();
}

class _DescriptionTextWidgetState extends State<DescriptionTextWidget> {
  String firstHalf;
  String secondHalf;

  bool flag = true;

  @override
  void initState() {
    super.initState();

    if (widget.text.length > 400) {
      firstHalf = widget.text.substring(0, 400);
      secondHalf = widget.text.substring(400, widget.text.length);
    } else {
      firstHalf = widget.text;
      secondHalf = "";
    }
  }


  @override
  Widget build(BuildContext context) {
    return new Container(
      padding: new EdgeInsets.symmetric(horizontal: 10.0, vertical: 10.0),
      child: secondHalf.isEmpty
          ? new Text(firstHalf, style: TextStyle(color: Colors.white))
          : new Column(
              children: <Widget>[
                new Text(
                  flag ? (firstHalf + "...") : (firstHalf + secondHalf),
                  style: TextStyle(color: Colors.white),
                ),
                new InkWell(
                  splashColor: Colors.transparent,
                  child: new Row(
                    mainAxisAlignment: MainAxisAlignment.end,
                    children: <Widget>[
                      new Text(
                        flag ? "show more" : "show less",
                        style:
                            new TextStyle(color: Colors.white.withOpacity(0.8)),
                      ),
                    ],
                  ),
                  onTap: () {
                    setState(() {
                      flag = !flag;
                    });
                  },
                ),
              ],
            ),
    );
  }
}

在我的主类中:我将文本“给”这个完整的小部件，如下所示:

 GestureDetector(
                    onTap: () async {

                    },
                    child: DescriptionTextWidget(
                        text: myString,
                  ),

如果我在主要的全状态小部件中更新了myString，则在全状态小部件'DescriptionTextWidget'中不会更新字符串。

更新DescriptionTextWidget类中的String的最佳方法是什么？

提前致谢!

Answer 1

Sample on DartPad

class DescriptionTextWidget extends StatefulWidget {
  final ValueNotifier<String> text;
}

class _DescriptionTextWidgetState extends State<DescriptionTextWidget> {
  @override
  void initState() {
    super.initState();
    widget.text.addListener(() => setState(initText));
    initText();
  }

  initText() {
    if (widget.text.value.length > 400) {
      firstHalf = widget.text.value.substring(0, 400);
      secondHalf = widget.text.value.substring(400, widget.text.value.length);
    } else {
      firstHalf = widget.text.value;
      secondHalf = "";
    }
  }
}

主类:

ValueNotifier<String> myString;

updateString(String value){
  myString.value = value;
}