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

[nesscx]

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 code without 'fading': https://gist.github.com/nesscx/721cd823350848e3d594ba95df68a7fa

[zoechi]

I think this would be a great StackOverflow question.

[nesscx]

https://stackoverflow.com/questions/51321804/how-to-fade-in-out-a-widget-from-sliverappbar-while-scrolling

[github-actions]

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