title: Flutter - Add Layers on top of ListView to scroll
body: <p>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:</p>
  <pre><code>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(&quot;Tap Left&quot;);
                  },
                ),
                GestureDetector(
                  child: Container(
                    width: mySize.width * 0.5,
                    color: Colors.red.withOpacity(0.5),
                  ),
                  onTap: () {
                    print(&quot;Tap RIGHT&quot;);
                  },
                ),
              ],
            ),
          ],
      ),
  );
  </code></pre>
  <p>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.</p>