Flutter - Add Layers on top of ListView to scroll - flutter

Question

I am making a reader app and I have a ListView.builder which is loading multiple Images from the API. Now I want to add a layer on top of the ListView with 2 transparent containers so that when I click the left container the list goes up and when I click the right container the list goes down. I tried adding the ListView to stack but then the scrolling ability of the list is gone. This is my code so far:
return Scaffold(
body: Stack(
children: [
ListView.builder(
controller: _scrollViewController,
cacheExtent: 1000,
itemCount: _picLinkMap.length,
itemBuilder: (BuildContext ctx, int index) {
return buildImageLoader(
_picLinkMap[index], index + 1);
},
),
Row(
children: [
GestureDetector(
child: Container(
width: mySize.width * 0.5,
color: Colors.black38,
),
onTap: () {
print("Tap Left");
},
),
GestureDetector(
child: Container(
width: mySize.width * 0.5,
color: Colors.red.withOpacity(0.5),
),
onTap: () {
print("Tap RIGHT");
},
),
],
),
],
),
);
I only want to scroll about half the height of the screen on tap.
I searched the web but did not find a suitable solution.

Answer 1

ScrollController _scrollViewController = ScrollController();
...
var jumpTo = (MediaQuery.of(context).size.height - 104)/2;
//104 is random number for the rest of the screen widgets (e.g. appbar ..)
_scrollViewController.jumpTo(jumpTo); //pixel value
...
ListView.builder(
controller: _scrollViewController,