How to get a variable of .dart file to another .dart file in flutter

Question

class widget_model extends StatelessWidget {
    final text;
    widget_model(this.text);

    String input = "";
    @override
    Widget build(BuildContext context) {
    return Expanded(
      child: Row(
        children: <Widget>[
          Expanded(
            child: Column(
              children: <Widget>[
    Container(
                  height: 60,
                  alignment: Alignment.center,
                  decoration: BoxDecoration(
                      gradient: LinearGradient(
                          colors: [Colors.pink, Colors.purpleAccent])),

                  child: InkWell(
                    onTap: () {
                      print("Pressed one");
                      print("The text is $input");
                      input=input+"1";
                      print("The text after $input");
                      Navigator.push(context, MaterialPageRoute(builder: (BuildContext)=>Homepage(input)));
                    },

                    child: Text(
                      "$text",
                      style: TextStyle(color: Colors.white, fontSize: 50),
                    ),
                  ),
                ),
              ],
            ),
          ),
          SizedBox(
            height: 10,
            width: 5,
          )
        ],
      ),
    );
  }
}

The variable 'input' in this.dart file has been declared within the stateless widget but how can I get this variable to another.dart file. How to be notified on change of the variable value.

Answer 1

You can do that in two ways

1. Use Provider package from pub.dev, and then you can use the variable in any other dart file. This is the preferred way for somewhat complex program.
2. You can just declare and initialize the variable outside the widget and than you can just use the variable in another dart file too. Like this,

String input = "";

class widget_model extends StatelessWidget {
final text;
widget_model(this.text);

@override
Widget build(BuildContext context) {
return Expanded(
  child: Row(
    children: <Widget>[
      Expanded(
        child: Column(
          children: <Widget>[
Container(
              height: 60,
              alignment: Alignment.center,
              decoration: BoxDecoration(
                  gradient: LinearGradient(
                      colors: [Colors.pink, Colors.purpleAccent])),

              child: InkWell(
                onTap: () {
                  print("Pressed one");
                  print("The text is $input");
                  input=input+"1";
                  print("The text after $input");
                  Navigator.push(context, MaterialPageRoute(builder: (BuildContext)=>Homepage(input)));
                },

                child: Text(
                  "$text",
                  style: TextStyle(color: Colors.white, fontSize: 50),
                ),
              ),
            ),
          ],
        ),
      ),
      SizedBox(
        height: 10,
        width: 5,
      )
    ],
  ),
);

Answer 2

For a clean approach, you need a state management library like provider to share the variable between two widgets if both widget are in a different branches in the tree. If the other widget that used the same variable is a child of the current one, you can use stateful widget and setState everytime the input value changes.