Building a High-Performance Android Wallpaper App with Kotlin & Retrofit
Learn how to consume NexWall Wallpaper REST API in Android Native with Kotlin, Coroutines, Flow, Retrofit2, and Glide with offline caching.
⚠️ Production Security Warning — Read Before Publishing to App Store
The code samples in this guide use a Bearer token directly in client-side mobile code. This is for local development and prototyping only.
Any API key or Bearer token embedded inside a compiled Android APK or iOS IPA can be extracted in under 60 seconds using free tools like jadx-gui or apktool.
For production apps on Google Play / App Store, always use a backend proxy architecture:
Your backend holds the NexWall Bearer token securely. It proxies requests from your app, adds auth, and returns responses — keeping your API key permanently hidden from reverse engineers. Read API Docs →
1. Setting Up Retrofit in Android Studio
Add the following dependencies in your app-level build.gradle.kts:
implementation("com.squareup.retrofit2:retrofit:2.9.0")
implementation("com.squareup.retrofit2:converter-gson:2.9.0")
implementation("io.coil-kt:coil:2.5.0")
implementation("org.jetbrains.kotlinx:kotlinx-coroutines-android:1.7.3")2. Kotlin Retrofit API Service
interface NexWallApiService {
@GET("api/developer/v1/wallpapers")
suspend fun getWallpapers(
@Header("Authorization") token: String = "Bearer YOUR_API_KEY",
@Header("Accept") accept: String = "application/json",
@Query("page") page: Int = 1,
@Query("per_page") perPage: Int = 30,
@Query("category_id") categoryId: Int? = null
): Response<WallpaperResponse>
}3. Jetpack Compose or XML Image Loading
Load the 4K wallpaper smoothly using Coil in Jetpack Compose:
AsyncImage(
model = wallpaper.thumbnailUrl,
contentDescription = "4K Wallpaper",
contentScale = ContentScale.Crop,
modifier = Modifier
.fillMaxWidth()
.aspectRatio(9f / 16f)
.clip(RoundedCornerShape(14.dp))
)Want to test this endpoint right now?
Use the interactive Live Sandbox Console to test queries without writing code.