How to make an API request in Kotlin?

Question

I am extremely new to Kotlin and APIs in general and can't find the syntax to create an API request using this language. I am creating a mobile version of a website so I'm using Android Studio to create a new UI for an already established backend. What are the steps and syntax to creating a request? Any help is deeply appreciated.

Answer 1

Once you have set your Android Studio to use Kotlin is pretty simple to do a REST call, and it's pretty much the same logic as with Java.

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Here's an example of a REST call with OkHttp:

build.gradle

dependencies {     //...     implementation 'com.squareup.okhttp3:okhttp:3.8.1' } 

AndroidManifest.xml

<uses-permission android:name="android.permission.INTERNET" /> 

MainActivity.kt

class MainActivity : AppCompatActivity() {      private val client = OkHttpClient()      override fun onCreate(savedInstanceState: Bundle?) {         super.onCreate(savedInstanceState)         setContentView(R.layout.activity_main)          run("https://api.github.com/users/Evin1-/repos")     }      fun run(url: String) {         val request = Request.Builder()                 .url(url)                 .build()          client.newCall(request).enqueue(object : Callback {             override fun onFailure(call: Call, e: IOException) {}             override fun onResponse(call: Call, response: Response) = println(response.body()?.string())         })     } } 

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Below are a few more complicated examples with other libraries:

• Network request in Kotlin with Retrofit
• Network request in Kotlin with Retrofit and coroutines
• Network request in Kotlin with Dagger, RxJava, Retrofit in MVP

Answer 2

I have create a sample API call using retrofit 2. Firstly, add these libraries in gradle

implementation "com.squareup.retrofit2:retrofit:2.3.0" implementation "com.squareup.retrofit2:adapter-rxjava2:2.3.0" implementation "com.squareup.retrofit2:converter-gson:2.3.0" implementation "io.reactivex.rxjava2:rxandroid:2.0.1" 

then create a class to configure Retrofit 2, say Connect.kt

class Connect {      companion object {          private fun getRetrofit(Url:String):Retrofit {             return Retrofit.Builder()                     .addCallAdapterFactory(                             RxJava2CallAdapterFactory.create())                     .addConverterFactory(                             GsonConverterFactory.create())                     .baseUrl(Url)                     .build()         }          fun getApiData():Retrofit{             val retrofitApi = getRetrofit(Url.BASE_URL)             return retrofitApi         }          fun callApi():CallApi{             val retrofitCall = getApiData()             return retrofitCall.create(CallApi::class.java)         }      } } 

I have created Url in Url class say Url.kt

class Url {     companion object {         const val BASE_URL = "your base url"         const val URL = "your url"     } } 

Created an interface for Api call

    interface CallApi {          @GET(Url.URL) //query needed if there is any query         fun getApi(@Query("limit") limit: Int): //model class is needed                 Observable<Model.Result>     } 

Create a model class according to your response, sample response is

{     "data": {         "children": [             {                 "data": {                     "author": "",                      "thumbnail":"",                       "title":""                      }                  }]           }  } 

for creating its model class, create an object say, Model

object Model {     data class Result(val data: Data)     data class Data(val children: List<Children>)     data class Children(val data: Datas)     data class Datas(val author: String,val thumbnail: String,val title: String) } 

Then create a boiler plate class to perform data fetch from api which can be called from any activity

class ApiData {     companion object {         const val count = 10         val api by lazy { Connect.callApi() }         var disposable: Disposable? = null         fun apiData(callback:Response){             disposable = api.getApi(count)                     .subscribeOn(Schedulers.io())                     .observeOn(AndroidSchedulers.mainThread())                     .subscribe ({                         result ->                         callback.data(result,true)                     }, { error ->                         error.printStackTrace()                     })          }      }     interface Response {         fun data(data:Model.Result,status:Boolean)     } } 

now it can be called from activity like,

ApiData.apiData( object :ApiData.Response{     override fun data(data: Model.Result, status: Boolean) {         if(status){             val items:List<Model.Children> = data.data.children         }     }  })