Make AppBar transparent and show background image which is set to whole screen

This is supported by Scaffold now (in stable - v1.12.13+hotfix.5).

• Set Scaffold extendBodyBehindAppBar to true,
• Set AppBar elevation to 0 to get rid of shadow,
• Set AppBar backgroundColor transparency as needed.

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      extendBodyBehindAppBar: true,
      backgroundColor: Colors.red,
      appBar: AppBar(
//        backgroundColor: Colors.transparent,
        backgroundColor: Color(0x44000000),
        elevation: 0,
        title: Text("Title"),
      ),
      body: Center(child: Text("Content")),
    );
  }

None of these seem to work for me, mine went something like this:

return Scaffold(
  extendBodyBehindAppBar: true,
  appBar: AppBar(
    backgroundColor: Colors.transparent,
    iconTheme: IconThemeData(color: Colors.white),
    elevation: 0.0,
  ),
  body: Stack(
    children: <Widget>[
      Container(
        decoration: BoxDecoration(
          image: DecorationImage(
            image: NetworkImage(
                'https://images.unsplash.com/photo-1517030330234-94c4fb948ebc?ixlib=rb-1.2.1&ixid=eyJhcHBfaWQiOjEyMDd9&auto=format&fit=crop&w=1275&q=80'),
            fit: BoxFit.cover,
          ),
        ),
        child: Padding(
          padding: const EdgeInsets.fromLTRB(0, 100, 0, 0),
          child:
          // Column of widgets here...
        ),
       ),
     ],
   ),
 );

You can use Scaffold's property "extendBodyBehindAppBar: true" Don't forget to wrap child with SafeArea

  @Override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(
          widget.title,
          style: TextStyle(color: Colors.black),
        ),
        backgroundColor: Colors.transparent,
        elevation: 0.0,
      ),
      extendBodyBehindAppBar: true,
      body: Container(
        width: double.infinity,
        height: double.infinity,
        decoration: BoxDecoration(
          image: DecorationImage(
            image: AssetImage('assets/background/home.png'),
            fit: BoxFit.cover,
          ),
        ),
        child: SafeArea(
            child: Center(
          child: Container(
            width: 300,
            height: 300,
            decoration: BoxDecoration(
              color: Colors.green,
            ),
            child: Center(child: Text('Test')),
          ),
        )),
      ),
    );
  }

you can use Stack widget to do so. Follow below example.

import 'package:flutter/material.dart';

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return new MaterialApp(
      home: new Home(),
    );
  }
}

class Home extends StatefulWidget {
  @override
  _HomeState createState() => _HomeState();
}

class _HomeState extends State<Home> {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Stack(
        children: <Widget>[
          Scaffold(
            backgroundColor: Colors.transparent,
            appBar: new AppBar(
              title: new Text(
                "Hello World",
                style: TextStyle(color: Colors.amber),
              ),
              backgroundColor: Colors.transparent,
              elevation: 0.0,
            ),
            body: new Container(
              color: Colors.red,
            ),
          ),
        ],
      ),
    );
  }
}