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Overview

The Random Images feature allows users to explore NASA’s vast Astronomy Picture of the Day archive by fetching multiple random images at once. This provides a serendipitous way to discover astronomical wonders from any point in APOD history.

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User Experience

1

Load Random Images

The screen fetches 5 random images from NASA’s APOD archive when launched.
2

Browse Collection

Scroll through the random selection, each displaying its title, date, and full explanation.
3

Manage Favorites

Each image has a favorite icon that reflects its saved state. Tap to add or remove from favorites.
4

Refresh for More

Load a new set of random images to continue exploring.
By default, the feature loads 5 random images per request, but this count is configurable.

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API Integration

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NASA API Endpoint

app/src/main/java/com/ccandeladev/nasaexplorer/data/api/NasaApiService.kt
interface NasaApiService {

    @GET("planetary/apod")
    suspend fun getRandomImages(
        @Query("api_key") apiKey: String,
        @Query("count") count: Int,
    ): List<NasaResponse>
}
Parameters:
  • api_key: NASA API authentication key
  • count: Number of random images to fetch (typically 5)
Returns: List of NasaResponse objects with random images from the APOD archive.

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Repository Implementation

app/src/main/java/com/ccandeladev/nasaexplorer/data/api/NasaRepository.kt
class NasaRepository @Inject constructor(private val nasaApiService: NasaApiService) {

    companion object {
        private const val API_KEY = BuildConfig.NASA_API_KEY
    }

    suspend fun getRandomImages(count: Int): List<NasaModel> {
        val response = nasaApiService.getRandomImages(apiKey = API_KEY, count = count)
        return response.map { it.toNasaModel() }
    }
}
The repository automatically transforms each NasaResponse into a NasaModel for UI consumption.

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ViewModel Architecture

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RandomImageViewModel

Manages state and business logic for random images:
app/src/main/java/com/ccandeladev/nasaexplorer/ui/randomimagescreen/RandomImageViewModel.kt
@HiltViewModel
class RandomImageViewModel @Inject constructor(
    private val nasaRepository: NasaRepository,
    private val firebaseAuth: FirebaseAuth,
    private val firebaseDatabase: FirebaseDatabase
) : ViewModel() {

    private val _randomImages = MutableStateFlow<List<NasaModel>>(emptyList())
    val randomImages: StateFlow<List<NasaModel>> = _randomImages

    private val _errorMessage = MutableStateFlow<String?>(null)
    val errorMessage: StateFlow<String?> = _errorMessage

    private val _isLoading = MutableStateFlow(false)
    val isLoading: StateFlow<Boolean> = _isLoading

    private val _favoriteStates = MutableStateFlow<Map<String, Boolean>>(emptyMap())
    val favoriteState: StateFlow<Map<String, Boolean>> = _favoriteStates

    fun loadRandomImages(count: Int = 5) {
        viewModelScope.launch {
            _isLoading.value = true

            try {
                val results = nasaRepository.getRandomImages(count = count)
                _randomImages.value = results
                _errorMessage.value = null
                checkFavorites(results.map { it.url })
            } catch (e: Exception) {
                _errorMessage.value = "Sin conexión a internet. Conéctate a una red Wi-Fi o habilita datos móviles para ver las imágenes"
                _randomImages.value = emptyList()
            } finally {
                _isLoading.value = false
            }
        }
    }
}

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State Management

The ViewModel exposes four reactive states:

randomImages

List of NasaModel objects representing the fetched random images.

isLoading

Boolean indicating whether images are currently being fetched.

errorMessage

Error message string for network or API failures.

favoriteStates

Map of URL to Boolean, tracking favorite status for each image.

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Favorites Management

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Tracking Multiple Favorites

Unlike the daily image screen, random images require tracking multiple favorite states simultaneously:
app/src/main/java/com/ccandeladev/nasaexplorer/ui/randomimagescreen/RandomImageViewModel.kt
private val _favoriteStates = MutableStateFlow<Map<String, Boolean>>(emptyMap())
val favoriteState: StateFlow<Map<String, Boolean>> = _favoriteStates
The map uses image URLs as keys and boolean values to indicate favorite status.

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Save to Favorites

app/src/main/java/com/ccandeladev/nasaexplorer/ui/randomimagescreen/RandomImageViewModel.kt
fun saveToFavorites(nasaModel: NasaModel) {
    val userId = firebaseAuth.currentUser?.uid

    if (userId != null) {
        viewModelScope.launch {
            try {
                val favoriteRef = firebaseDatabase.reference
                    .child("favorites")
                    .child(userId)
                    .push()
                
                val favoriteImage = mapOf(
                    "id" to (favoriteRef.key ?: ""),
                    "title" to nasaModel.title,
                    "url" to nasaModel.url
                )
                
                favoriteRef.setValue(favoriteImage).await()

                val currentState = _favoriteStates.value.toMutableMap()
                currentState[nasaModel.url] = true
                _favoriteStates.value = currentState
            } catch (e: Exception) {
                _errorMessage.value = "Error al guardar favorito ${e.message}"
            }
        }
    } else {
        _errorMessage.value = "Usuario no autenticado"
    }
}

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Remove from Favorites

app/src/main/java/com/ccandeladev/nasaexplorer/ui/randomimagescreen/RandomImageViewModel.kt
fun removeFromFavorites(nasaModel: NasaModel) {
    val userId = firebaseAuth.currentUser?.uid

    if (userId != null) {
        viewModelScope.launch {
            try {
                val favoriteRef = firebaseDatabase.reference
                    .child("favorites")
                    .child(userId)
                
                val snapshot = favoriteRef
                    .orderByChild("url")
                    .equalTo(nasaModel.url)
                    .get()
                    .await()

                for (child in snapshot.children) {
                    child.ref.removeValue().await()
                }

                val currentState = _favoriteStates.value.toMutableMap()
                currentState[nasaModel.url] = false
                _favoriteStates.value = currentState
            } catch (e: Exception) {
                _errorMessage.value = "Error al borrar favorito ${e.message}"
            }
        }
    }
}

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Check Favorites Status

Automatically checks which images are already favorited:
app/src/main/java/com/ccandeladev/nasaexplorer/ui/randomimagescreen/RandomImageViewModel.kt
private fun checkFavorites(urls: List<String>) {
    val userId = firebaseAuth.currentUser?.uid
    if (userId != null) {
        viewModelScope.launch {
            try {
                val favoriteRef = firebaseDatabase.reference
                    .child("favorites")
                    .child(userId)
                
                val snapshot = favoriteRef.get().await()
                val currentState = _favoriteStates.value.toMutableMap()

                for (url in urls) {
                    currentState[url] = snapshot.children.any { 
                        it.child("url").value == url 
                    }
                }
                _favoriteStates.value = currentState
            } catch (e: Exception) {
                _errorMessage.value = "Error al cargar estado de favorito ${e.message}"
            }
        }
    }
}
The checkFavorites() function is automatically called after images load, ensuring favorite icons display correct state immediately.

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UI Implementation

Accessing favorite state for a specific image: 
val randomImages by viewModel.randomImages.collectAsState()
val favoriteStates by viewModel.favoriteState.collectAsState()

randomImages.forEach { image ->
    val isFavorite = favoriteStates[image.url] ?: false
    
    // Display image with favorite button
    ImageCard(
        nasaModel = image,
        isFavorite = isFavorite,
        onFavoriteClick = {
            if (isFavorite) {
                viewModel.removeFromFavorites(image)
            } else {
                viewModel.saveToFavorites(image)
            }
        }
    )
}

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Firebase Database Structure

Random images share the same favorites structure as other features: 
favorites/
  └── {userId}/
      ├── {pushId1}/
      │   ├── id: "{pushId1}"
      │   ├── title: "Random Image 1"
      │   └── url: "https://..."
      └── {pushId2}/
          ├── id: "{pushId2}"
          ├── title: "Random Image 2"
          └── url: "https://..."

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Error Handling

Displays network error message and resets image list to empty.
Caught and displayed via the errorMessage state flow.
Shows authentication error when attempting favorite operations without login.
All Firebase operations are wrapped in try-catch blocks with specific error messages.

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Developer Guide

1

Inject ViewModel

@Composable
fun RandomImageScreen(
    randomImageViewModel: RandomImageViewModel = hiltViewModel()
) {
    // Implementation
}
2

Collect States

val randomImages by randomImageViewModel.randomImages.collectAsState()
val isLoading by randomImageViewModel.isLoading.collectAsState()
val favoriteStates by randomImageViewModel.favoriteState.collectAsState()
3

Load Images

LaunchedEffect(Unit) {
    randomImageViewModel.loadRandomImages(count = 5)
}
4

Handle Favorite Actions

IconButton(
    onClick = {
        if (favoriteStates[image.url] == true) {
            randomImageViewModel.removeFromFavorites(image)
        } else {
            randomImageViewModel.saveToFavorites(image)
        }
    }
) {
    Icon(
        imageVector = if (favoriteStates[image.url] == true) 
            Icons.Filled.Star else Icons.Outlined.Star,
        contentDescription = "Favorite"
    )
}
Always check for null values when accessing the favoriteStates map, as images may not have a favorite state entry yet.

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Performance Considerations

  • The default count of 5 images balances discovery with API rate limits
  • Favorite status is checked in a single Firebase query for all loaded images
  • State updates use immutable map operations to ensure proper UI reactivity
Random images are selected by NASA’s API from the entire APOD archive, so you may occasionally see the same image across different loads.

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