flutter background image with gradient code example

Example: flutter container background gradient

appBar: AppBar(

      title: Text('Flutter Demo'),
      flexibleSpace: Container(
        decoration: BoxDecoration(
          gradient: LinearGradient(
            begin: Alignment.centerLeft,
            end: Alignment.centerRight,
            colors: <Color>[
              Colors.red,
              Colors.blue
            ],
          ),
        ),
      ),
    ),