Android App Startup Optimization: What to Measure and What to Fix First

@RunWith(AndroidJUnit4::class)
class StartupBenchmark {

    @get:Rule
    val benchmarkRule = MacrobenchmarkRule()

    @Test
    fun coldStartup() = benchmarkRule.measureRepeated(
        packageName = "com.example.app",
        metrics = listOf(StartupTimingMetric()),
        startupMode = StartupMode.COLD,
        iterations = 10,
    ) {
        pressHome()
        startActivityAndWait()
    }
}

// In the first screen, once it is usable:
class MainActivity : ComponentActivity() {
    private fun onContentReady() {
        reportFullyDrawn() // Without this there is no TTFD
    }
}

// app/build.gradle.kts
plugins {
    id("com.android.application")
    id("androidx.baselineprofile")
}

dependencies {
    implementation("androidx.profileinstaller:profileinstaller:1.4.1")
    baselineProfile(project(":baseline-profile"))
}

// An initializer: what to create, and what it depends on
class CrashReportingInitializer : Initializer<CrashReporter> {

    override fun create(context: Context): CrashReporter {
        return CrashReporter.init(context)
    }

    override fun dependencies(): List<Class<out Initializer<*>>> {
        // Initialized first, automatically
        return listOf(AnalyticsInitializer::class.java)
    }
}

// AndroidManifest.xml: take it out of automatic startup
//
// <provider
//     android:name="androidx.startup.InitializationProvider"
//     android:authorities="${applicationId}.androidx-startup"
//     android:exported="false"
//     tools:node="merge">
//     <meta-data
//         android:name="com.example.CrashReportingInitializer"
//         tools:node="remove" />
// </provider>

// At the first place the component is needed
AppInitializer.getInstance(context)
    .initializeComponent(CrashReportingInitializer::class.java)

@Composable
fun HomeScreen(viewModel: HomeViewModel) {
    val uiState by viewModel.uiState.collectAsStateWithLifecycle()

    Column {
        // Draws on the first frame, needs no data
        TopBar(title = "Home")

        when (val state = uiState) {
            is HomeState.Loading -> LoadingPlaceholder()
            is HomeState.Success -> {
                LazyColumn {
                    items(state.items) { item ->
                        ContentCard(item)
                    }
                }
            }
            is HomeState.Error -> ErrorBanner(state.message)
        }
    }
}