1. build.gradle (Module: app)
2. สำรวจ API ของ Github
3. สร้าง class
4. สร้าง API interface
5. สร้าง TextView ไว้แสดงผล
6. MainActivity
7. ขอสิทธิ์

• Retrofit Android Example JSON Parser in Kotlin

สร้างโปรเจ็กส์ชื่อ RetrofitDemo ภาษา Kotlin เพื่ออ่าน API ของ Github

1.build.gradle (Module: app)

dependencies {
    ...
    implementation 'com.squareup.retrofit2:retrofit:2.4.0'
    implementation 'com.squareup.retrofit2:converter-gson:2.4.0'
}

2.สำรวจ API ของ Github

API ของ Github https://api.github.com/search/users?q=rokano

{
  "total_count": 7,
  "incomplete_results": false,
  "items": [
    {
      "login": "rokanost",
      "id": 5094636,
      "node_id": "MDQ6VXNlcjUwOTQ2MzY=",
      "avatar_url": "https://avatars0.githubusercontent.com/u/5094636?v=4",
      "gravatar_id": "",
      "url": "https://api.github.com/users/rokanost",
      "html_url": "https://github.com/rokanost",
      "followers_url": "https://api.github.com/users/rokanost/followers",
      "following_url": "https://api.github.com/users/rokanost/following{/other_user}",
      "gists_url": "https://api.github.com/users/rokanost/gists{/gist_id}",
      "starred_url": "https://api.github.com/users/rokanost/starred{/owner}{/repo}",
      "subscriptions_url": "https://api.github.com/users/rokanost/subscriptions",
      "organizations_url": "https://api.github.com/users/rokanost/orgs",
      "repos_url": "https://api.github.com/users/rokanost/repos",
      "events_url": "https://api.github.com/users/rokanost/events{/privacy}",
      "received_events_url": "https://api.github.com/users/rokanost/received_events",
      "type": "User",
      "site_admin": false,
      "score": 32.160065
    },
    { ...}
    ....
  ]
}

3.สร้าง class

ไฟล์ Users.kt

package com.phaisarn.retrofitdemo

class Users {
    var id: Int = 0
    var login: String = ""
    var score: Float = 0.0f
}

ไฟล์ UsersList.kt

package com.phaisarn.retrofitdemo

import com.google.gson.annotations.SerializedName

class UsersList {
    @SerializedName("items")
    var users: List<Users>? = null
}

4.สร้าง API interface

ไฟล์ Api.java

package com.phaisarn.retrofitdemo;

import retrofit2.Call;
import retrofit2.http.GET;

public interface Api {
    //urls
    @GET("users?q=rokano")
    Call<UsersList> getUsers();
}

5.สร้าง TextView ไว้แสดงผล

ไฟล์ main_activity.xml

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout
        xmlns:android="http://schemas.android.com/apk/res/android"
        xmlns:tools="http://schemas.android.com/tools"
        xmlns:app="http://schemas.android.com/apk/res-auto"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        tools:context=".MainActivity">

    <TextView
            android:id="@+id/tv_users"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_marginTop="8dp"
            android:scrollbars="vertical"
            android:text="Hello World!"
            android:textColor="@color/colorPrimaryDark"
            android:textSize="16sp"
            app:layout_constraintBottom_toBottomOf="parent"
            app:layout_constraintHorizontal_bias="0.051"
            app:layout_constraintLeft_toLeftOf="parent"
            app:layout_constraintRight_toRightOf="parent"
            app:layout_constraintTop_toTopOf="parent"
            app:layout_constraintVertical_bias="0.032"/>

</androidx.constraintlayout.widget.ConstraintLayout>

6. MainActivity

ไฟล์ MainActivity.kt

package com.phaisarn.retrofitdemo

import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import android.widget.TextView
import android.util.Log
import retrofit2.Retrofit
import retrofit2.converter.gson.GsonConverterFactory
import retrofit2.Call
import retrofit2.Callback
import retrofit2.Response

class MainActivity : AppCompatActivity() {
    val BASE_URL = "https://api.github.com/search/"
    var tv_user: TextView? = null
    var str: String = ""

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

        tv_user = findViewById(R.id.tv_users)
        getUsers()
    }

    // function to call server and update ui
    fun getUsers() {
        var retrofit: Retrofit = Retrofit.Builder()
            .baseUrl(BASE_URL)
            .addConverterFactory(GsonConverterFactory.create())
            .build()

        var api = retrofit.create(Api::class.java)
        var call = api.users
        call.enqueue(object : Callback<UsersList> {

            override fun onResponse(call: Call<UsersList>?, response: Response<UsersList>?) {
                var usres = response?.body()
                var user = usres?.users
                var length = user!!.size

                for (i in 0 until length) {
                    str = str + "\n" + user.get(i).id + " " + user.get(i).login
                }

                tv_user!!.text = str
            }

            override fun onFailure(call: Call<UsersList>?, t: Throwable?) {
                Log.v("Error", t.toString())
            }
        })
    }
}

7.ขอสิทธิ์

ไฟล์ AndroidManifest.xml

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