how to execute the VoidCallback in flutter

user_2441637 0
Viewed 19664

I'm trying to test the VoidCallback so I created the main file, that have a function called from a flat button in the widget, which is in a separate file, but did not work.

main.dart

import 'package:flutter/material.dart';
import 'controller_test.dart';

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Retrieve Text Input',
      home: MyCustomForm(),
    );
  }
}

// Define a Custom Form Widget
class MyCustomForm extends StatefulWidget {
  @override
  _MyCustomFormState createState() => _MyCustomFormState();
}

class _MyCustomFormState extends State<MyCustomForm> {
  final myController = TextEditingController();

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

    myController.addListener(_printLatestValue);
  }

  _printLatestValue() {
    print("Second text field: ${myController.text}");
  }

  _test() {
    print("hi there");
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Retrieve Text Input'),
      ),
      body: Con(_test, myController)
    );
  }
}

controller_test.dart

import 'package:flutter/material.dart';

class Con extends StatelessWidget {
  Con(this.clickCallback, this.tc);
  final TextEditingController tc;
  final VoidCallback clickCallback;

  @override
  Widget build(BuildContext context) {
    return Padding(
      padding: const EdgeInsets.all(16.0),
      child: Column(
        children: <Widget>[
          TextField(
            onChanged: (text) {
              print("First text field: $text");
            },
          ),
          TextField(
            controller: tc,
          ),
          FlatButton(
            onPressed: () => clickCallback,
            child: Text("click me"),
          )
        ],
      ),
    );
  }
}

When I click the FlatButton in the widget, nothing is happening, I was expecting hi there to be printed

dart flutter
4 Answers

there are two options here.

  1. onPressed: () => fun() is like onPressed argument is an anonymous method that calls fun.

  2. onPressed: fun is like onPressed argument is the function fun.

user_25547450

I just found it in another answer here I was missing the (), so correct call is:

      FlatButton(
        onPressed: () => clickCallback(),
        child: Text("click me"),
      )
user_24416370

In your callback make sure to call setState if any variables change. I repopulate an list in my provider and then use assign that list to the variable list which I convert into a list of cards. The variable list needs state refreshed to see it.

user_40011770

You can get callback from stateless widget to your current page by using Voidcallback class.

Just add this custom widget in your current page (widget.build() function)

DefaultButton(
        buttonText: Constants.LOGIN_BUTTON_TEXT,
        onPressed: () => validateInputFields(),
        size: size,
      );

My custom widget class is

class DefaultButton extends StatelessWidget {

  DefaultButton({this.buttonText, this.onPressed, this.size});

  final String buttonText;
  final VoidCallback onPressed;
  final Size size;

  @override
  Widget build(BuildContext context) {
    return MaterialButton(
      minWidth: size.width,
      onPressed: () => onPressed(), //callback to refered page
      padding: EdgeInsets.all(0.0),
      shape: RoundedRectangleBorder(
        borderRadius: BorderRadius.circular(DEFAULT_BORDER_RADIUS),
      ),
      child: Ink(
        width: size.width,
        decoration: BoxDecoration(
          gradient: LinearGradient(
            begin: Alignment.centerLeft,
            end: Alignment.centerRight,
            colors: <Color>[
              SECONDARY_COLOR_SHADE_LITE,
              SECONDARY_COLOR_SHADE_DARK,
            ],
          ),
          borderRadius: BorderRadius.circular(DEFAULT_BORDER_RADIUS),
        ),
        child: Padding(
            padding: EdgeInsets.only(left: 20, right: 20, top: 12, bottom: 12),
            child: Text(
              buttonText,
              style: Theme.of(context).textTheme.button,
              textAlign: TextAlign.center,
            )),
      ),
    );
  }
}
user_105799690
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