android-kotlin

## When to use this skill

Use this skill whenever the user wants to:
- Create Android applications using Kotlin with Activities, Fragments, or Jetpack Compose
- Implement ViewModel, LiveData, StateFlow, or other Jetpack architecture components
- Configure Gradle build files (build.gradle.kts), dependencies, or build variants
- Set up navigation, permissions, or Android lifecycle handling
- Build and sign APK/AAB for release or configure ProGuard

## How to use this skill

### 1. Project Setup

Create a new project with Android Studio or configure build files:

```kotlin
// build.gradle.kts (app module)
plugins {
    id("com.android.application")
    id("org.jetbrains.kotlin.android")
}

dependencies {
    implementation("androidx.core:core-ktx:1.12.0")
    implementation("androidx.lifecycle:lifecycle-viewmodel-ktx:2.7.0")
    implementation("androidx.navigation:navigation-fragment-ktx:2.7.6")
}
```

### 2. Architecture (MVVM with ViewModel)

```kotlin
class MainViewModel : ViewModel() {
    private val _items = MutableStateFlow<List<Item>>(emptyList())
    val items: StateFlow<List<Item>> = _items.asStateFlow()

    fun loadItems() {
        viewModelScope.launch {
            _items.value = repository.getItems()
        }
    }
}
```

### 3. UI with Jetpack Compose

```kotlin
@Composable
fun ItemList(viewModel: MainViewModel = viewModel()) {
    val items by viewModel.items.collectAsState()
    LazyColumn {
        items(items) { item ->
            Text(text = item.name, modifier = Modifier.padding(16.dp))
        }
    }
}
```

### 4. Navigation

Register destinations in the navigation graph and navigate programmatically:

```kotlin
findNavController().navigate(R.id.action_home_to_detail)
```

## Best Practices

- Use `viewModelScope` for coroutines tied to ViewModel lifecycle; avoid leaking activities.
- Save UI state with `SavedStateHandle` in ViewModel; handle process death gracefully.
- Use ViewBinding or Jetpack Compose instead of `findViewById`.
- Apply ProGuard/R8 rules for release builds; keep signing keys secure.
- Test with `@RunWith(AndroidJUnit4::class)` and Espresso for UI tests.

## Resources

- https://developer.android.com/kotlin
- https://developer.android.com/jetpack/compose
- https://developer.android.com/topic/architecture

## Keywords

android, Kotlin, Jetpack, Compose, ViewModel, Navigation, Gradle, AndroidManifest.xml