flutter can not access images from assets and network code example

Example 1: flutter asset image not showing

flutter:  
  uses-material-design: true   
  assets:   
    - assets/

class _UserLoginState extends State<UserLogin> {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Stack(
        children: <Widget>[
          Image(image: AssetImage("assets/christmas.jpeg"),
          fit: BoxFit.cover,
        ],
      )
    );
  }
}

Example 2: image.network flutter not working

<uses-permission android:name="android.permission.INTERNET" />
<uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" /="android.permission.ACCESS_NETWORK_STATE" />>