how to execute the VoidCallback in flutter - dart

Question

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

Answer 1

there are two options here.
onPressed: () => fun() is like onPressed argument is an anonymous method that calls fun.
onPressed: fun is like onPressed argument is the function fun.

Answer 2

I just found it in another answer here
I was missing the (), so correct call is:
FlatButton(
onPressed: () => clickCallback(),
child: Text("click me"),
)

Answer 3

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,
)),
),
);
}
}

Answer 4

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.