设置背景图还是挺简单的，直接container里加个decration然后加个图片就行了，就像这样

import 'package:flutter/material.dart';

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  MyHomePage({Key key, this.title}) : super(key: key);
  final String title;

  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
        appBar: AppBar(
          title: Text(widget.title),
        ),
        body: Container(
            decoration: BoxDecoration(
          image: DecorationImage(
            image: NetworkImage(
                'https://img.zcool.cn/community/0372d195ac1cd55a8012062e3b16810.jpg'),
            fit: BoxFit.cover,
          ),
        )));
  }
}

可以看到，appbar的部位并没有背景图，我们要做的就是全屏透明，把appbar那部分也要透明带上背景，这个需求也很简单

代码如下

import 'package:flutter/material.dart';

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  MyHomePage({Key key, this.title}) : super(key: key);
  final String title;

  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  @override
  Widget build(BuildContext context) {
    return Container(
        decoration: BoxDecoration(
            image: DecorationImage(
          image: NetworkImage(
              'https://img.zcool.cn/community/0372d195ac1cd55a8012062e3b16810.jpg'),
          fit: BoxFit.cover,
        )),
        child: Scaffold(
            backgroundColor: Colors.transparent, //把scaffold的背景色改成透明
            appBar: AppBar(
              backgroundColor: Colors.transparent, //把appbar的背景色改成透明
              // elevation: 0,//appbar的阴影
              title: Text(widget.title),
            ),
            body: Center(
              child: Text('Hello World'),
            )));
  }
}

效果长这样

这就达到了我们想要的效果了，可以看到appbar那里还有个阴影，要去掉的话只要把上面代码的

// elevation: 0,//appbar的阴影

注释掉就行了

那么状态栏的全透明沉浸呢

在main.dart 的runapp后面加上

SystemUiOverlayStyle systemUiOverlayStyle = SystemUiOverlayStyle(statusBarColor: Colors.transparent);
SystemChrome.setSystemUIOverlayStyle(systemUiOverlayStyle);

就可以了

状态栏沉浸来自

https://www.jianshu.com/p/97e93c82ccef