How to fade in/out a widget from SliverAppBar while scrolling?

Question

I want to \'fade in\' and \'fade out\' a widget from SliverAppBar when user scrolls on the screen.

This is an example of what I want to do:

Here is my c

Answer 1

This is actually quite simple using ScrollController and the Opacity Widget. Here's a basic example:

https://gist.github.com/smkhalsa/ec33ec61993f29865a52a40fff4b81a2