Update some of our ListView samples with CustomScrollViews

[Piinks]

ListView is very very common in examples, but for a lot of scrolling effects, hey are more easily and performantly achieved with a CustomScrollView.

In general, a lot of users start with a ListView, and then nest additional scrolling contents within using shrinkwrap. This is an anti-pattern. By including more examples of CustomScrollView in places like

• the website
• the API docs
• Flutter Gallery
• flutter/samples
• codelabs
• cookbooks

and elsewhere, we can make this option more readily available to developers. To be clear, we don't need to remove use of ListView - just pepper in an even balance of CustomScrollView as well.

[domesticmouse]

Is there a specific codelab that you can see that this would make sense with? Most of the codelabs are intended to be on the beginner friendly side, and thus only contain a list of items, at best. I feel like CustomScrollView is a concept which requires more explanation, and only makes sense when combining it with more complex user interfaces.

With that said, I am more than happy to workshop a "Advanced ScrollViews" codelab, especially when 2D scrolling becomes a thing. Q3?

[Piinks]

Happy to collaborate on this!

CustomScrollView is a concept which requires more explanation, and only makes sense when combining it with more complex user interfaces.

The goal here is to make CustomScrollView less scary. It does not necessarily have to mean advanced and complex (!!!). Often times a CustomScrollView can solve a simple use case, but users avoid it because of the perception. As a result, users instead use inefficient scrolling compositions and end up with performance issues. Making CustomScrollView more approachable I think would be very helpful.

For example, a user may create a ListView and want a grid within the same scroll view. They more often do something like this:

ListView(
  children: [
    // ... list items ...
    GridView(shrinkwrap: true)
    // ... more list items ...
  ]
)

When they could do

CustomScrollView(
  slivers: [
    SliverList(...)
    SliverGrid(...)
    SliverList(...)
  ]
)

[Piinks]

Also related: #8434 :)