What is wrong with my code? It only shows a black screen - flutter

Question

I am trying to make an application and now what I want to do is just create a container with shadows.
It said dead code so I deleted some code, and tried some other things.
import 'package:flutter/material.dart';
import 'package:flutter/rendering.dart';
class appBar extends StatelessWidget {
appBar({this.title});
final Widget title;
#override
Widget build(BuildContext context) {
return Container(
height: 60.0,
padding: const EdgeInsets.all(10.0));
decoration: new BoxDecoration(color: Colors.cyan[500]);
child: Container(
decoration: new BoxDecoration(
boxShadow:[
BoxShadow(
color: Colors.black12,
blurRadius: 20,
spreadRadius: 4.0,
offset: Offset(
8.0,
8.0,
)
),
]
));
}
}
I expected a container but I got a black screen.

Answer 1

Instead of using decoration in Container to get the color. Just add color widget to your container. An example is as follows
return Container(
color:Colors.cyan
)

Answer 2

You see a black screen when you are missing a material widget. Wrapping the whole widget in a Scafold works.
I also see some wrong syntax, so here's the fix.
class appBar extends StatelessWidget {
appBar({this.title});
final Widget title;
#override
Widget build(BuildContext context) {
return Scaffold(
body: Container(
height: 60.0,
padding: const EdgeInsets.all(10.0),
decoration: new BoxDecoration(color: Colors.cyan[500]),
child: Container(
decoration: new BoxDecoration(
boxShadow: [
BoxShadow(
color: Colors.black12,
blurRadius: 20,
spreadRadius: 4.0,
offset: Offset(
8.0,
8.0,
),
),
],
),
),
),
);
}
}

Answer 3

You have to warp your container with Scaffold widget. and you will get reslove your issue !! enjoy.because in flutter scaffold provide black screen with white canvas.

Answer 4

There were too many mistakes in your code, you unnecessarily used ; at the end of every line, and make sure your class name start with capital letter.
Here is the 100% working code.
void main() => runApp(MaterialApp(home: MyAppBar(title: "AppBar")));
class MyAppBar extends StatelessWidget {
MyAppBar({this.title});
final String title;
#override
Widget build(BuildContext context) {
return Scaffold(
body: SafeArea(
child: Container(
height: 60.0,
width: double.maxFinite,
padding: const EdgeInsets.all(10.0),
decoration: new BoxDecoration(color: Colors.cyan[500]),
child: Container(
child: Text(title ?? ''),
decoration: new BoxDecoration(
boxShadow: [
BoxShadow(
color: Colors.black12,
blurRadius: 20,
spreadRadius: 4.0,
offset: Offset(8.0, 8.0),
),
],
),
),
),
),
);
}
}

Answer 5

appBar is not a nice class name. The convention is to start a class name with a capital letter. So AppBar would be nicer;
But AppBar is a flutter defined class, so... not a good choice;
your code has some ";" where you should have "," instead (you are inside of a Container function call, not a normal code body) Ex: padding: const EdgeInsets.all(10.0));
So i made corrections and tested your code this way (this is my main.dart file in a newly created flutter project):
import 'package:flutter/material.dart';
void main() => runApp(MyApp());
class MyApp extends StatelessWidget {
// This widget is the root of your application.
#override
Widget build(BuildContext context) {
return MaterialApp(
title: 'Flutter Demo',
theme: ThemeData(
// This is the theme of your application.
//
// Try running your application with "flutter run". You'll see the
// application has a blue toolbar. Then, without quitting the app, try
// changing the primarySwatch below to Colors.green and then invoke
// "hot reload" (press "r" in the console where you ran "flutter run",
// or simply save your changes to "hot reload" in a Flutter IDE).
// Notice that the counter didn't reset back to zero; the application
// is not restarted.
primarySwatch: Colors.blue,
),
home: MyHomePage(title: 'Flutter Demo Home Page'),
);
}
}
class MyHomePage extends StatefulWidget {
MyHomePage({Key key, this.title}) : super(key: key);
// This widget is the home page of your application. It is stateful, meaning
// that it has a State object (defined below) that contains fields that affect
// how it looks.
// This class is the configuration for the state. It holds the values (in this
// case the title) provided by the parent (in this case the App widget) and
// used by the build method of the State. Fields in a Widget subclass are
// always marked "final".
final String title;
#override
_MyHomePageState createState() => _MyHomePageState();
}
class _MyHomePageState extends State<MyHomePage> {
int _counter = 0;
void _incrementCounter() {
setState(() {
// This call to setState tells the Flutter framework that something has
// changed in this State, which causes it to rerun the build method below
// so that the display can reflect the updated values. If we changed
// _counter without calling setState(), then the build method would not be
// called again, and so nothing would appear to happen.
_counter++;
});
}
#override
Widget build(BuildContext context) {
// This method is rerun every time setState is called, for instance as done
// by the _incrementCounter method above.
//
// The Flutter framework has been optimized to make rerunning build methods
// fast, so that you can just rebuild anything that needs updating rather
// than having to individually change instances of widgets.
return AppBarCustom(title: Text('teste'));
}
}
class AppBarCustom extends StatelessWidget {
AppBarCustom({this.title});
final Widget title;
#override
Widget build(BuildContext context) {
return Container(
height: 60.0,
padding: const EdgeInsets.all(10.0),
decoration: new BoxDecoration(color: Colors.cyan[500]),
child: Container(
decoration: new BoxDecoration(
color: Colors.white,
boxShadow: [
BoxShadow(
color: Colors.black,
blurRadius: 20,
spreadRadius: 10.0,
offset: Offset(
8.0,
8.0,
)),
],
),
),
);
}
}
I added a white background color to your inner Container just to show it more clearly and messed with the shadows...
Note your class at the end of the code.
He is the final rendering: