Flutter - calling setState() from other widget

Question

Is it possible to call setState() of particular widget (embedded in other widgets) from other widgets onPressed() method so only that

Answer 1

I'm a beginner of flutter.

This is my modified version, not sure if there is anything wrong via this way, but it works.

1. Add key value in class MyTextWidget

MyTextWidget({Key key}):super(key:key);

2. Declare a GlobalKey in class MyHomePage

GlobalKey<_MyTextWidgetState> textGlobalKey = new GlobalKey<_MyTextWidgetState>();

3. Add MyTextWidget widget

MyTextWidget(key: textGlobalKey);

4. Call _updateSeconds() in _addPressed()

void _addPressed() {
  //somehow call _updateSeconds()
  textGlobalKey.currentState._updateSeconds(_seconds++);
}

All code:

import 'package:flutter/material.dart';
void main() => runApp(new MyApp());

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return new MaterialApp(
      title: 'Timer',
      theme: new ThemeData(
        primaryColor: Colors.grey.shade800,
      ),
      home: new MyHomePage(),
    );
  }
}

class MyHomePage extends StatelessWidget {

  GlobalKey<_MyTextWidgetState> textGlobalKey = new GlobalKey<_MyTextWidgetState>();

  int _seconds = 1;

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text("title"),
      ),
      body: Column(
        mainAxisAlignment: MainAxisAlignment.spaceAround,
        children: [
          MyTextWidget(key: textGlobalKey), //just update this widget
          Divider(),
          Row(
            mainAxisAlignment: MainAxisAlignment.spaceAround,
            children: [
              IconButton(
                icon: Icon(Icons.add_circle),
                onPressed: _addPressed,
                iconSize: 150.0,
              ),
              IconButton(
                icon: Icon(Icons.remove_circle),
                onPressed: ()=> print("to be implemented"),
                iconSize: 150.0,
              ),
            ],
          )
        ],
      ),
    );
  }

  void _addPressed() {
    //somehow call _updateSeconds()
    textGlobalKey.currentState._updateSeconds(_seconds++);
  }
}

class MyTextWidget extends StatefulWidget{

  MyTextWidget({Key key}):super(key:key);

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

class _MyTextWidgetState extends State {

  int secondsToDisplay = 0;

  void _updateSeconds(int newSeconds) {
    setState(() {
      secondsToDisplay = newSeconds;
    });
  }

  @override
  Widget build(BuildContext context) {
    return Text(
      secondsToDisplay.toString(),
      textScaleFactor: 5.0,
    );
  }
}

Hope it helps :)