Background image in Sliver appbar

// TYPE1: This will show a provided color when pinned
flexibleSpace: FlexibleSpaceBar(
  background: Image.network("https://wallpaperseven.com/wallpapers/Grey-Abstract-4k-Wallpaper-scaled.jpg", fit: BoxFit.cover,),
)

//TYPE2: This will show background image when pinned
flexibleSpace: Stack(
  children: <Widget>[
    Positioned.fill(
      child: Image.network(
        "https://wallpaperseven.com/wallpapers/Grey-Abstract-4k-Wallpaper-scaled.jpg",
        fit: BoxFit.cover,
      )
    )
  ],
),

//TYPE3: This will hide the content of flexibleSpace when pinned
flexibleSpace: FlexibleSpaceBar(
  background: Stack(
    children: <Widget>[
      Positioned.fill(
        child: Image.asset(
          "assets/banner.jpg",
          fit: BoxFit.cover,
        )
      ),
    ],
  ),
)