如何将变量作为参数传递给小部件二,在那里修改它,然后 return 将修改后的值传递给小部件一,Flutter

how to pass a variable as a parameter to a widget two, modify it there, and return the modified value to widget one, Flutter

如何将变量作为参数传递给小部件二,在那里修改它,然后 return 将修改后的值传递给小部件一。 我需要在单击“更改”按钮时更改变量的值,并且该更改会反映在小部件一中。

class FirstWidget extends StatefulWidget {
  @override
  _FirstWidgetState createState() => _FirstWidgetState();
}
class FirstWidgetState extends State<FirstWidget> {
String c = 'start';
        @override
        Widget build(BuildContext context){
            return Container(
                child: SecondWidget(variable: c),
            );
        }
    }
    class SecondWidget extends StatefulWidget {
    String variable;
    SecondWidget({ this.variable });
  @override
  _SecondWidgetState createState() => _SecondWidgetState();
}
    class SecondWidgetState extends State<SecondWidget> {
        @override
        Widget build(BuildContext context){
            return Container(
                child: RaisedButton(child:Text('Change it'), onPressed: () {widget.variable = 'end';}),

            );
        }
    }

可以通过回调轻松实现它,这意味着您将一个函数传递给您的第二个小部件,当您单击按钮时调用该函数,这样您就可以在第一个小部件中修改任何您想要的内容。

像这样:

class FirstWidget extends StatefulWidget {
  @override
  _FirstWidgetState createState() => _FirstWidgetState();
}
class FirstWidgetState extends State<FirstWidget> {
String c = 'start';
        @override
        Widget build(BuildContext context){
            return Container(
                child: SecondWidget(variable: c, onChange: (newVal) {
                    setState(() {c = newVal;});
                 }),
            );
        }
    }
    class SecondWidget extends StatefulWidget {
    String variable;
    final onChange;

    SecondWidget({ this.variable, this.onChange });
  @override
  _SecondWidgetState createState() => _SecondWidgetState();
}
    class SecondWidgetState extends State<SecondWidget> {
        @override
        Widget build(BuildContext context){
            return Container(
                child: RaisedButton(child:Text('Change it'), onPressed: () {widget.onChange('end');}),

            );
        }
    }