Patterning Dagger/Hilt Cases Where a Module Is or Is Not Required

 

🧑🏻‍💻 When a Module Is Not Required: Concrete Classes

In Hilt/Dagger, concrete classes with an @Inject constructor can be injected automatically.


class ApiClient @Inject constructor()

class UserRepository @Inject constructor(
    private val api: ApiClient
)

Point:
If the class can be instantiated directly, a Module is not required.

 

🧑🏻‍💻 When a Module Is Required (1): Interfaces

When injecting an interface, Hilt cannot determine which implementation to use.

You need to specify it explicitly using @Binds inside a Module.


interface Logger { 
    fun log(msg: String) 
}

class ConsoleLogger @Inject constructor() : Logger

@Module
@InstallIn(SingletonComponent::class)
interface LoggerModule {
    @Binds
    fun bindLogger(impl: ConsoleLogger): Logger
}

Point:
Interfaces always require a Module.

 

🧑🏻‍💻 When a Module Is Required (2): External Libraries

External libraries typically do not have @Inject constructor.

You must provide the creation logic inside a Module.


@Module
@InstallIn(SingletonComponent::class)
object NetworkModule {
    @Provides
    fun provideClient(): OkHttpClient = OkHttpClient.Builder().build()
}

Point:
You make external classes injectable by defining how to create them in a Module.

 

🧑🏻‍💻 Summary

  • Your own concrete classes → auto-injectable
  • Interfaces & external libraries → Module required
  • Multiple implementations or singleton handling → use @Qualifier, @Named, @Singleton

👉 Dagger/HiltでModuleが必要か一目でわかるようにパターン化する

Kotlin StateFlow: value vs. update – Which One Should You Use?

When updating a MutableStateFlow, you have two options. Here is how to decide instantly.

 

🧑🏻‍💻 The Golden Rule

  • Use update { } if the new value depends on the current value (e.g., incrementing a counter, toggling a boolean).
  • Use value = if you are completely overwriting the state (e.g., setting a loading state, resetting data).

 

🧑🏻‍💻 Why does it matter?

Direct assignment (value = ...) is not thread-safe for "read-modify-write" operations.

If two coroutines try to update the state simultaneously using .value = .value + 1, you risk a Race Condition where one update is lost.

The update function is atomic. It uses a Compare-And-Set mechanism to ensure that updates happen sequentially and safely, even across multiple threads.

 

🧑🏻‍💻 Code Comparison

❌ Risky (Race Condition prone)


// If called concurrently, updates might be lost
_uiState.value = _uiState.value.copy(count = _uiState.value.count + 1)

✅ Safe (Thread-safe)


// Guarantees consistency
_uiState.update { it.copy(count = it.count + 1) }

✅ Safe (Overwrite)


// No race condition risk because we ignore the previous state
_uiState.value = UiState.Loading

 

🧑🏻‍💻 Summary

When in doubt, use update. It is safer by default and prevents subtle concurrency bugs.

Why are updates to Kotlin, Compose, and KSP such a hassle?

In Android development, you're constantly dealing with the same set of three: Kotlin, the Compose Compiler, and KSP.

They seem like a friendly group, but their update schedules are always completely different! You upgrade Kotlin, and the Compose Compiler isn't compatible. You change something, and KSP throws a build error because of an internal API change...

To better manage this "dependency triangle" situation, the main idea is to use Renovate's configuration to treat them as a single unit. The simple plan is: "Raise all Kotlin ecosystem dependencies at the same time!"

 

🧑🏻‍💻 Brief overview of the renovate.json file


{
  "$schema": "https://docs.renovatebot.com/renovate-schema.json",
  "extends": [
    "config:base",
    "group:all",
    ":dependencyDashboard",
    "schedule:daily"
  ],
  "baseBranches": ["main"],
  "commitMessageExtra": "{{{currentValue}}} to {{#if isPinDigest}}{{{newDigestShort}}}{{else}}{{#if isMajor}}{{prettyNewMajor}}{{else}}{{#if isSingleVersion}}{{prettyNewVersion}}{{else}}{{#if newValue}}{{{newValue}}}{{else}}{{{newDigestShort}}}{{/if}}{{/if}}{{/if}}{{/if}}",
  "packageRules": [
    {
      "matchPackagePatterns": ["androidx.compose.compiler:compiler"],
      "groupName": "kotlin"
    },
    {
      "matchPackagePatterns": ["org.jetbrains.kotlin.*"],
      "groupName": "kotlin"
    },
    {
      "matchPackagePatterns": ["com.google.devtools.ksp"],
      "groupName": "kotlin"
    }
  ]
}

👉 architecture-samples/renovate.json at main · android/architecture-samples

Roughly summarized, here are the key points:

  • groupName: "kotlin" to bundle dependencies This setting specifies that the three elements—the Compose Compiler, Kotlin, and KSP—should be treated as belonging to the "same group." This allows Renovate to update them all together at once.
  • schedule: daily for a calm update pace This checks for updates once a day. You'll receive pull requests (PRs) on a daily basis, preventing a huge influx of dependency updates all at once, which makes things much easier to manage.
  • commitMessageExtra to see changes at a glance The version difference, like "2.0.10 → 2.0.20," is automatically added to the PR title. It's a small tweak, but surprisingly useful.

Setting up your configuration this way significantly reduces the tragedy of "Kotlin got updated, but Compose broke..."

 

🧑🏻‍💻 What We Found While Using It

Once this setup is in place, you can feel much more confident testing updates for everything Kotlin-related. Renovate diligently checks daily, automatically creating a PR whenever a new version drops.

But there's one small warning:

The Compose Compiler sometimes takes a little extra time to catch up to the latest Kotlin version. So, don't just merge the PR when you see it—it's highly recommended to verify the CI status first.

KSP is similar; because it depends on Kotlin's internal workings, it's safer to update it along with Kotlin and run your tests together.

 

🧑🏻‍💻 Summary: Teach Renovate that "These Three Are a Set"

The configuration we discussed treats the trio of Kotlin, the Compose Compiler, and KSP as a single group.

  • Bundle all Kotlin-related dependencies for simultaneous updates.
  • Check for updates at a manageable daily pace.
  • See version differences directly in the PR title.

Just implementing this significantly reduces the problems caused by versions getting out of sync and breaking your build.

💡 Key Takeaway: Use Renovate less as an "automatic update tool" and more as a "dependency rulebook."

We simply need to tell Kotlin, Compose, and KSP to cooperate and "work together."

👉 Kotlin・Compose・KSP の更新、どうしてこんなに面倒なの?