flutter ListView KeepAlive after some scroll

I want to keepAlive my widgets which are already rendered in ListView. I was tried with addAutomaticKeepAlives:true properties which provide by ListView class.

Here is my sample code which I was used. Same issue in SliverChildBuilderDelegate delegate which provide by SliverList.

ListView.builder(    itemBuilder: (context,index){      return Card(        child: Container(          child: Image.asset("images/${index+1}.jpg",fit: BoxFit.cover,),          height: 250.0,        ),      );    },    addAutomaticKeepAlives: true,    itemCount:40 ,);