JSON to Kotlin Data Class Generator Online

Which library should I use for data parsing in Kotlin?

You just can use GSON which is developed by google. GSON Link: https://github.com/google/gson

Gradle implementation of GSON:

	dependencies {
		implementation 'com.google.code.gson:gson:2.9.0' // Gradle
		// implementation("com.google.code.gson:gson:2.9.0") // Gradle KTS
	}
	

GSON is not for only Android you can use it in your any Kotlin or JAVA project. Here is an example use of GSON:

	val myJson = """
	{
	    "user_name": "john123",
	    "email": "john@example.com",
	    "name": "John Doe"
	}
	""".trimIndent()

	val gson = Gson()
	var mUser = gson.fromJson(myJson, UserData::class.java)
	println(mUser.userName)
	

How do you make a network call with retrofit, GSON and Coroutine in MVVM pattern in your Android project?

1. Add Below all libraries(Gradle KTS), If you are using gradle make some chage.

	implementation("com.squareup.retrofit2:retrofit:2.9.0")
    implementation("com.squareup.retrofit2:converter-gson:2.7.1")
    implementation("com.google.code.gson:gson:2.9.0")

    implementation("com.squareup.okhttp3:logging-interceptor:4.4.0") // for cache
    implementation("androidx.lifecycle:lifecycle-extensions:2.2.0")
    implementation("androidx.lifecycle:lifecycle-viewmodel-ktx:2.3.1")
    implementation("androidx.lifecycle:lifecycle-runtime-ktx:2.3.1")
    implementation("org.jetbrains.kotlinx:kotlinx-coroutines-android:1.4.3")

See this file for all libraries

2. Get json string from your api response.

3. Copy and paste the json to json2kt.com web site and download converted .kt files in a zip file.

4. Extract zip file and place converted .kt files to your project package.

5. Now make a new package, recommended name is: “networkService”

6. Place below 4 files in this package:

First file: AllApi.kt

	object AllApi {

	    private external fun baseUrlFromJNI(boolean: Boolean): String

	    const val BASE_URL = "https://api.example.com/"

	    private const val V1 = "v1/"

	    const val DATA_LIST = V1 + "my_data.php"
	}
	

Second file: ApiState.kt

	sealed class ApiState {
	    	object Loading : ApiState()
	    	class Failure(val e: Throwable) : ApiState()
	    	class Success(val data: Any) : ApiState()
	    	object Empty : ApiState()
	}
	

Third file: RetrofitClient.kt

	object RetrofitClient {

	    private const val TIME_OUT: Long = 120

	    private val gson = GsonBuilder().setLenient().create()

	    private val okHttpClient = OkHttpClient.Builder()
	        .readTimeout(TIME_OUT, TimeUnit.SECONDS)
	        .connectTimeout(TIME_OUT, TimeUnit.SECONDS)
	        .addInterceptor { chain ->
	            val resp = chain.proceed(chain.request())
	            // Deal with the response code
	            if (resp.code() == 200) {
	                try {
	                    val myJson = resp.peekBody(2048).string() // peekBody() will not close the response
	                    println(myJson)
	                } catch (e: Exception) {
	                    println("Error parse json from intercept..............")
	                }
	            } else { 
	                println(resp)
	            }
	            resp
	        }.build()

	    val retrofit: RetrofitInterface by lazy {
	        Retrofit.Builder()
	            .addConverterFactory(GsonConverterFactory.create(gson))
	            .baseUrl(AllApi.BASE_URL)
	            .client(okHttpClient)
	            .build().create(RetrofitInterface::class.java)
	    }

	}
	

Fourth File: RetrofitInterface.kt

	interface RetrofitInterface {

    	@GET(AllApi.DATA_LIST)
    	suspend fun getDataList(): List

	}
	

7. Now you need to make a call of your api. So make a package named “repository” and create a file inside of it, file name can be like “MyDataRepository.kt” and class inside of it will be MyDataRepository.

Example Repository code:

	class MyDataRepository {

	    fun getDataList(): Flow> = flow {
	        val r = RetrofitClient.retrofit.getDataList()
	        emit(r)
	    }.flowOn(Dispatchers.IO)

	}
	

8. Now you need to create a ViewModel. So make a new package, add a kotlin file inside of it and file name can be like this: MyDataVM.kt and class name can be like : MyDataVM Code example of ViewModel:

	class MyDataVM(private var repository: MyDataRepository) : ViewModel() {

	    val myDataList: MutableStateFlow = MutableStateFlow(ApiState.Empty)

	    fun getDataList() = viewModelScope.launch {
	        myDataList.value = ApiState.Loading
	        repository.getDataList()
	            .catch { e ->
	                myDataList.value = ApiState.Failure(e)
	            }.collect { data ->
	                myDataList.value = ApiState.Success(data)
	            }
	    }

	}
	

9. Now we need to make a view model factory class (Ex: File Name: MyDataViewModelFactory.kt and Class name: MyDataViewModelFactory) to transfer our repository class inside of view model.

Example ViewModelFactory:

	
		class MyDataViewModelFactory(private val repository: MyDataRepository): ViewModelProvider.Factory {
		    override fun  create(modelClass: Class): T {
		        return MyDataVM(repository) as T
		    }
		}
	

10. Now it is time to make an instance of view model. So go to your fragment or activity and create an instance of view model like below:

	private lateinit var myDataVM: MyDataVM

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        
        myDataVM = ViewModelProvider(
            this,
            MyDataViewModelFactory(MyDataRepository())
        )[MyDataVM::class.java]

    }
	

11. Now call api using the function like below, it is generally can call inside onCreate of activity or onViewCreated of a fragment:

		myDataVM.getDataList()
	

12. Where is my data after calling api? Now you need to observe the api to get data. See below example:

	 lifecycleScope.launchWhenCreated {
	            myDataVM.myDataList.collect {
	                apiStateCheck(binding.indicator, it) { mData ->
	                    val myObj = mData as List
	                    // TODO Here is your rest of the code with myObj
	                }
	        }
	  }
	

13. You may be thiking about apiStateCheck function? Oh here is your function below. Keep it inside any kotlin file without any class so you can just import the class when you need again.

	lifecycleScope.launchWhenCreated {
	    myDataVM.myDataList.collect {
	        apiStateCheck(binding.indicator, it) { mData ->
	            val myObj = mData as List
	            // TODO Here is your rest of the code with myObj
	        }
	    }
	}
	

This is how you can use GSON, Retrofit with MVVM pattern.

Complete source code is here: GitHub: Android-Modern-API-Call-Kotlin-MVVM

Thanks.