What to Expect When You're Expecting... Jetpack Compose

New Talk, Who Dis?

New Talk, Who Dis?

A Brief Compose History

Because Compose Hasn't Been Around Long

• Announced at Google I|O 2019
• First bits released fall 2019
• Role: replacement UI framework
• Timeline
  • Now: developer preview
  • "Summer 2020": alpha
  • 2021: stable

A Bit Of Composin'

@Composable
fun NewsStory() {
    val image = imageResource(R.drawable.header)

    Column(modifier = Modifier.padding(16.dp)) {
        val imageModifier = Modifier
            .preferredHeightIn(maxHeight = 180.dp)
            .fillMaxWidth()

        Image(image, modifier = imageModifier,
                  contentScale = ContentScale.Crop)

        HeightSpacer(16.dp)

        Text("A day in Shark Fin Cove")
        Text("Davenport, California")
        Text("December 2018")
    }
}

class MainActivity : AppCompatActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContent {
            NewsStory()
        }
    }
}

Revisiting Google and Kotlin

Those Who Do Not Learn From History...

• 2017: Oh, you're interested in Kotlin?
• 2018: We support Kotlin!
• 2019: Kotlin first!
  • But we still support Java!
  • (hint: they said that once about Eclipse)

Talent Acquisition

Developers Don't Grow on Trees (Usually)

• Hiring Android talent has been tough... until 2020 upended matters
• Being considered "behind the times" makes that tougher
• How long before you can't land talent because you're using Java?
• Reasonably likely that Compose will have a similar effect

Why We Care Now

Versus, Y'know, Later

• Do you remember how that Kotlin migration went?
• Migrating to Compose will be narrower yet more complicated
  • Narrower: effects grow closer you get to the UI rendering
  • Complicated: less automatic tool support, most likely
• Perfect Planning Prevents Poor Production... Perhaps

What We Want

Besides Fewer Murder Hornets

• Minimize transition pain... with minimal extraneous prep work, in case Compose fizzles
• Identify opportunities to improve the apps... as Compose itself is largely a lateral move

Kotlinize!

All The Things! Mostly!

• Compose relies upon a Kotlin compiler plugin to perform its magic
• Net: Java ain't walkin' through that door
• By the time Compose is mainstream, Java will be tech debt

Clean Up Your Layouts

They're Probably Crufty

• Move everything you can into styles, themes, dimension resources, etc.
  • Those still have roles in Compose
  • More tools/libraries to assist, such as Accompanist
• Objective: minimize what is in the layouts, since those get rewritten

Go Easy on Data Binding

Can't Make an Omelette...

• Data binding is tied to layout resources
• Layout resources are going away (mostly)
• Net: your binding expressions will need to get replaced
• Maybe don't change what you have, but perhaps don't add more to the pile

A Bit More Composin'

private data class AgreementViewState(
  val terms: Boolean,
  val privacy: Boolean
) {
  fun canProceed() = terms && privacy
}

@Composable
fun Agreement() {
  Column(
    verticalArrangement = Arrangement.SpaceAround,
    horizontalGravity = Alignment.CenterHorizontally
  ) {
    val viewState = state { AgreementViewState(terms = false, privacy = false) }

    Column(horizontalGravity = Alignment.Start) {
      Row(horizontalArrangement = Arrangement.Start) {
        Checkbox(
          checked = viewState.value.terms,
          onCheckedChange = { viewState.value = viewState.value.copy(terms = it) }
        )
        Spacer(modifier = Modifier.preferredWidth(4.dp))
        Text(text = "I agree to the terms and conditions")
      }

      Spacer(modifier = Modifier.preferredHeight(8.dp))

      Row(horizontalArrangement = Arrangement.Start) {
        Checkbox(
          checked = viewState.value.privacy,
          onCheckedChange = { viewState.value = viewState.value.copy(privacy = it) }
        )
        Spacer(modifier = Modifier.preferredWidth(4.dp))
        Text(text = "I agree to the privacy policy")
      }

      Spacer(modifier = Modifier.preferredHeight(8.dp))

      Text(text = if (viewState.value.canProceed()) "You may proceed!" else "Please indicate your agreement")
    }
  }
}

Even More Composin'

(Insert Android Studio Here)

Clean Up Your Architectures

Yes, All of Them

• Compose designed for unidirectional data flows
  • State flows down
  • Events flow up
• Widgets are not stateful
• May require some tweaking of your approaches (e.g., two-way data binding)
• Consistent architecture will simplify migration

Identify Tactical UI Improvements

Make Google Happy! Users Too!

• Landscape?
• Dark mode?
• Split-screen?

Ponder Moonshots

Crew Dragon Has Touchscreens, So...

• Things that are "game changers" that Compose might make easier to achieve
• Example: Desktop via ui-desktop
  • Kotlin/Multiplatform
  • Windows/macOS/Linux via the JVM
  • Can you expand your market with modest re-engineering?

Budget Play Time

Skin Your Knees Early!

• By the time Compose reaches beta, try to start experimenting
• Partly, so you can learn and use that knowledge to better steer your plans
• Partly, so you can tell us what you need to succeed
  • Tell your favorite GDE
  • Tell your favorite Compose library maintainer
  • Tell #compose on Kotlinlang Slack (or DM me there)

Prepare Arguments for Management

Or Perhaps Just Gentle Conversations

• Why are we bothering with Compose? (recruiting)
• Will this interrupt our delivery schedules? (hopefully not, using progressive replacement)
• How does this help our users? (tactical UI changes plus moontshots)
• How does this help the CEO's golf game? (you're on your own for that one)

R-E-L-A-X

What? Wrong QB?

• Expect a significant hype train
• All the cool kids will be slinging Compose code
• You will get your turn too
• Do right by your users and your team, and don't Compose without a plan

Where To Get This Presentation