title: Flutter floating button hide and show on whether ListView index
body: <p>I have an app that has a ListView and Floating Button. I wanted to hide the Floating Button if Index 0 in the ListView is shown and show the Floating Button when Index 0 is not shown in the ListView. Most of the information in the web (including Stackoverflow) covers hiding the button when scrolling (direction) and not based on the index shown by ListView.</p>