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How to use custom converter with Retrofit in Kotlin Android

How to use custom converter with Retrofit in Kotlin Android.

Here is a detailed step-by-step tutorial on how to use a custom converter with Retrofit in Kotlin Android:

Step 1: Add Retrofit to your project​

First, you need to add the Retrofit dependency to your project. Open your app-level build.gradle file and add the following line to the dependencies block:

implementation 'com.squareup.retrofit2:retrofit:2.9.0'

Sync your project to include the Retrofit library.

Step 2: Create a custom converter​

To use a custom converter with Retrofit, you need to create a class that implements the Converter.Factory interface. This class will be responsible for converting the response body to your desired type.

Here's an example of a custom converter that converts the response body to a list of custom objects:

import com.squareup.moshi.Moshi
import okhttp3.ResponseBody
import retrofit2.Converter
import retrofit2.Retrofit
import java.lang.reflect.Type

class CustomConverterFactory(private val moshi: Moshi) : Converter.Factory() {
    override fun responseBodyConverter(
        type: Type,
        annotations: Array<Annotation>,
        retrofit: Retrofit
    ): Converter<ResponseBody, *>? {
        val adapter = moshi.adapter<List<CustomObject>>(type)
        return Converter<ResponseBody, List<CustomObject>> { value ->
            adapter.fromJson(value.string()) ?: emptyList()
        }
    }
}

In this example, we're using the Moshi library for JSON parsing. You can replace CustomObject with your desired object class.

Step 3: Create a Retrofit instance​

Next, you need to create a Retrofit instance and configure it to use your custom converter. Here's an example of how to do it:

import com.squareup.moshi.Moshi
import retrofit2.Retrofit
import retrofit2.converter.moshi.MoshiConverterFactory

val moshi = Moshi.Builder().build()

val retrofit = Retrofit.Builder()
    .baseUrl("https://api.example.com/")
    .addConverterFactory(CustomConverterFactor(moshi))
    .build()

In this example, we're using the MoshiConverterFactory provided by Retrofit to convert the response body. We pass our custom converter factory to the addConverterFactory method.

Make sure to replace the baseUrl with your actual API endpoint.

Step 4: Define your API interface​

Now, you can define your API interface using Retrofit annotations. Here's an example:

interface ApiService {
    @GET("data")
    suspend fun getData(): List<CustomObject>
}

In this example, we're using the @GET annotation to specify the API endpoint and the suspend keyword to make the API call asynchronous.

Step 5: Make API calls​

Finally, you can use the Retrofit instance and the API interface to make API calls. Here's an example:

val apiService = retrofit.create(ApiService::class.java)

GlobalScope.launch(Dispatchers.IO) {
    try {
        val data = apiService.getData()
        // Do something with the data
    } catch (e: Exception) {
        // Handle the error
    }
}

In this example, we're using coroutines to make the API call asynchronously. You can handle the response data or any error that occurs in the try-catch block.

That's it! You have now successfully used a custom converter with Retrofit in Kotlin Android. Feel free to customize the converter and API interface according to your requirements.