Click button in child widget not detected in parent function-CodePudding

I am trying to understand how state works with Flutter, I have a child widget that needs to change something in the Parent widget. I can detect the push on the button in the child using a print. However when i try to bubble up this change to the parent its not catching it.

I have been though a number of tutorials and im not 100% sure I understand how state works or should work, I think I am missing something here.

import 'package:flutter/material.dart';

void main() => runApp(const MyApp());

class MyApp extends StatelessWidget {
  const MyApp({super.key});

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      debugShowCheckedModeBanner: false,
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: const MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  const MyHomePage({super.key, required this.title});

  final String title;

  @override
  State<MyHomePage> createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  int _counter = 0;

  //Consider this function as your _onNotification and important to note I am using setState() within :)
  void _incrementCounter() {
    print("pressed");  // Does not detect pressed.
    setState(() {
      _counter  ;    // counter is not increased
    });
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(
          widget.title,
          style: TextStyle(color: Colors.white),
        ),
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            Text(
              'You have pushed the button $_counter times:',
              style: TextStyle(fontSize: 20.0, fontWeight: FontWeight.bold),
            ),
          ],
        ),
      ),
      floatingActionButton: MyFloatButton(
          _incrementCounter), //Pass delegate to _incrementCounter method
    );
  }
}

class MyFloatButton extends StatefulWidget {

  // Here I am receiving the function in constructor as params
  const MyFloatButton(this.onPressedFunction, {super.key});

  // Should be the delegated function from _MyHomePageState
  final Function onPressedFunction;

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

class _MyFloatButtonState extends State<MyFloatButton> {
  @override
  Widget build(BuildContext context) {
    return Container(
      padding: EdgeInsets.all(5.0),
      decoration: BoxDecoration(
          color: Colors.orangeAccent,
          borderRadius: new BorderRadius.circular(50.0)),
      child: IconButton(
        icon: Icon(Icons.add),
        color: Colors.white,
        onPressed: () => {
          //print('pressed')  // Does work shows button pressed
          widget.onPressedFunction
        }, // call the delegated method to detect the pressed
      ),
    );
  }
}

Things tried:

onPressed: widget.onPressedFunction()

Results in

setState() or markNeedsBuild called during build

onPressed: widget.onPressedFunction

Results in

The argument type 'Function' can't be assigned to the parameter type 'void Function()?'.

onPressed: () => widget.onPressedFunction,

Results in

No change does not do anything

CodePudding user response：

Please try this. onPressedFunction is a function so declare like below function.

onPressed: () => {
      widget.onPressedFunction()
    },

CodePudding user response：

Inside the MyFloatButton you're calling a function inside a function

 onPressed: () => {
          //print('pressed')  // Does work shows button pressed
          widget.onPressedFunction
        },

It should be as follows

 onPressed: widget.onPressedFunction

CodePudding user response：

Change this

onPressed: () => {
      //print('pressed')  // Does work shows button pressed
      widget.onPressedFunction
    },

To this

onPressed: () => widget.onPressedFunction,

Just remove curly braces and add () here

floatingActionButton: MyFloatButton(
      _incrementCounter())