You need to provide child and onPressed parameter in order to render the widget, else it won't render, which results in non working UI.
Check out the code i modified :
import 'package:flutter/material.dart';
final Color darkBlue = Color.fromARGB(255, 18, 32, 47);
void main() {
runApp(MyApp());
}
class MyApp extends StatelessWidget {
@override
Widget build(BuildContext context) {
return MaterialApp(
theme: ThemeData.dark().copyWith(scaffoldBackgroundColor: darkBlue),
debugShowCheckedModeBanner: false,
home: Scaffold(
body: Center(
child: MyWidget(),
),
),
);
}
}
class MyWidget extends StatelessWidget {
@override
Widget build(BuildContext context) {
return MaterialApp(
home: SafeArea(
child: Scaffold(
body: Column(
crossAxisAlignment: CrossAxisAlignment.stretch,
children: [
FlatButton(
color: Colors.red,
onPressed:()=>printData(),
child: Text("click"),
),
FlatButton(
color: Colors.green,
onPressed:()=>printData(),
child: Text("click"),
),
FlatButton(
color: Colors.blue,
onPressed:()=>printData(),
child: Text("click"),
),
],
),
),
));
}
}
void printData(){
print('Hello');
}