Migrate 'Discover' to Jetpack Compose

[chrisbanes]

Line diff

You might see the line diff (+669, −633) and wonder why it increased 😲. Well, Tivi was (actually still is) a heavy user of the data-binding and Epoxy combo. They both code-generate lots of magic, but the line diff you see is only my code. I reckon if we included the generated code in there... 📈

Lazy* DSL

Instead of Epoxy + Data Binding, we're now using the new (experimental) Lazy[Column|Row] DSL. They make creating complex scrolling UIs much easier to build, and more efficient due to the windowing!

As a quick overview, it allows you to build complex scrolling UIs like so:

• For rows with unique content, you can wrap them in an item { /* content */ } 😍. Content can be whatever you want:

item { Header(...) }
item { Carousel(...) }

• You can add lists of items via items() and itemsIndexed():

items(list) { item ->
   MyItemRow(item)
}

• Sticky header support is also coming soon 🥳

To see it in action, checkout the root layout in this screen here.

Epoxy + Data Binding

I found it interesting how close the state paths from my old EpoxyController are to the new Compose implementation. Obviously there are differences, but the general structure is pretty close.

Migration notes

This has not quite been a 1:1 migration though:

• It's now missing a swipe-to-refresh feature, due to the lack of nested scrolling in Compose.
• Data-set updates in the LazyRows aren't animated (yet).