Kotlin Android Barcode Nutrition API Example

Barcode scanning is the feature users expect on Android calorie trackers. This Kotlin Android barcode nutrition API example shows CameraX capture, Retrofit networking, and UPC lookup through Calorie API without exposing your key in the APK.

What You Will Build

1. Scan UPC/EAN with CameraX
2. Call your backend barcode endpoint
3. Display calories and macros
4. Log a portion in grams

Dependencies

// build.gradle.kts (app)
implementation("androidx.camera:camera-camera2:1.3.1")
implementation("androidx.camera:camera-view:1.3.1")
implementation("com.google.mlkit:barcode-scanning:17.2.0")
implementation("com.squareup.retrofit2:retrofit:2.9.0")
implementation("com.squareup.retrofit2:converter-gson:2.9.0")

Retrofit Interface (Backend Proxy)

interface NutritionApi {
    @GET("api/foods/barcode/{upc}")
    suspend fun lookupBarcode(@Path("upc") upc: String): FoodDetailResponse

    @GET("api/foods/search")
    suspend fun searchFoods(
        @Query("q") query: String,
        @Query("limit") limit: Int = 15
    ): FoodSearchResponse
}

data class FoodDetailResponse(
    val id: Int,
    val name: String,
    val brand: String?,
    val calories: Double?,
    val protein_g: Double?,
    val carbohydrates_g: Double?,
    val fat_g: Double?
)

val api = Retrofit.Builder()
    .baseUrl("https://your-backend.example.com/")
    .addConverterFactory(GsonConverterFactory.create())
    .build()
    .create(NutritionApi::class.java)

Base URL points at Firebase or Next.js proxy, not Calorie API directly.

Barcode Analyzer

@OptIn(ExperimentalGetImage::class)
class BarcodeAnalyzer(
    private val onBarcode: (String) -> Unit
) : ImageAnalysis.Analyzer {
    private val scanner = BarcodeScanning.getClient()

    override fun analyze(imageProxy: ImageProxy) {
        val mediaImage = imageProxy.image ?: return
        val input = InputImage.fromMediaImage(mediaImage, imageProxy.imageInfo.rotationDegrees)
        scanner.process(input)
            .addOnSuccessListener { barcodes ->
                barcodes.firstOrNull()?.rawValue?.let(onBarcode)
            }
            .addOnCompleteListener { imageProxy.close() }
    }
}

Lookup and Display

class BarcodeViewModel(private val api: NutritionApi) : ViewModel() {
    private val _food = MutableStateFlow<FoodDetailResponse?>(null)
    val food = _food.asStateFlow()

    fun onBarcodeScanned(upc: String) {
        if (!upc.matches(Regex("^\\d{8,14}$"))) return
        viewModelScope.launch {
            try {
                _food.value = api.lookupBarcode(upc)
            } catch (e: Exception) {
                _food.value = null
            }
        }
    }
}

Validate UPC format before calling upstream.

Scale Portion

fun scale(per100g: Double, grams: Double) = (grams / 100.0) * per100g

Handle Scan Failures

Open Food Facts barcodes may be missing branded data. Calorie API indexes packaged foods with verified macros. See Open Food Facts rate limits for production tradeoffs.

Related Guides

• Flutter food database tutorial
• Capacitor Ionic barcode backend
• Food barcode lookup API

Get free API key | Docs