AndroidでJSONオブジェクトを解析する方法は？

この例は、AndroidでJSONオブジェクトを解析する方法を示しています。

ステップ1 − Android Studioで新しいプロジェクトを作成し、[ファイル]⇒[新しいプロジェクト]に移動して、新しいプロジェクトを作成するために必要なすべての詳細を入力します。

ステップ2 −次の依存関係をGradleスクリプトに追加します⇒build.gradleand do sync

apply plugin: 'com.android.application'
android {
   compileSdkVersion 28
   defaultConfig {
      applicationId "com.example.sample"
      minSdkVersion 21
      targetSdkVersion 28
      versionCode 1
      versionName "1.0"
      testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"
   }
   buildTypes {
      release {
         minifyEnabled false
         proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro'
      }
   }
}
dependencies {
   implementation fileTree(dir: 'libs', include: ['*.jar'])
   implementation 'com.android.support:appcompat-v7:28.0.0'
   implementation 'com.android.support.constraint:constraint-layout:1.1.3'
   testImplementation 'junit:junit:4.12'
   androidTestImplementation 'com.android.support.test:runner:1.0.2'
   androidTestImplementation 'com.android.support.test.espresso:espresso-core:3.0.2'
   implementation "com.android.support:recyclerview-v7:23.0.1" // dependency file for RecyclerView
   implementation 'com.android.support:cardview-v7:23.0.1' // dependency file for CardView
}

ステップ3 −次の依存関係をres / layout / activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="https://schemas.android.com/apk/res/android"
   xmlns:app="https://schemas.android.com/apk/res-auto"
   xmlns:tools="https://schemas.android.com/tools"
   android:layout_width="match_parent"
   android:layout_height="match_parent"
   tools:context=".MainActivity">
   <android.support.v7.widget.RecyclerView
      android:id="@+id/recyclerView"
      android:layout_width="match_parent"
      android:layout_height="match_parent" />
</RelativeLayout>

ステップ4 −次の依存関係をres / layout / rowlayout _main.xml

<?xml version="1.0" encoding="utf-8"?>
<android.support.v7.widget.CardView xmlns:android="https://schemas.android.com/apk/res/android"
   xmlns:card_view="https://schemas.android.com/apk/res-auto"
   android:id="@+id/cardView"
   android:layout_width="match_parent"
   android:layout_margin="5dp"
   android:layout_height="wrap_content">
   <LinearLayout
      android:layout_width="match_parent"
      android:layout_height="wrap_content"
      android:orientation="vertical"
      android:padding="10dp">
      <!--items for a single row of RecyclerView-->
      <TextView
         android:id="@+id/tvName"
         android:layout_width="wrap_content"
         android:layout_height="wrap_content"
         android:text="Name"
         android:textColor="#000"
         android:textSize="20sp" />
      <TextView
         android:id="@+id/tvEmail"
         android:layout_width="wrap_content"
         android:layout_height="wrap_content"
         android:text="email@email.com"
         android:textColor="#000"
         android:textSize="15sp" />
      <TextView
         android:id="@+id/tvMobile"
         android:layout_width="wrap_content"
         android:layout_height="wrap_content"
         android:text="e9999999999"
         android:textColor="#000"
         android:textSize="15sp" />
      </LinearLayout>
</android.support.v7.widget.CardView>

ステップ5 −次の依存関係をsrc / MainActivity.java

package com.example.sample;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.support.v7.widget.LinearLayoutManager;
import android.support.v7.widget.RecyclerView;
import android.util.Log;
import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;
import java.io.IOException;
import java.io.InputStream;
import java.util.ArrayList;
import java.util.Arrays;
public class MainActivity extends AppCompatActivity {
   // ArrayList for person names, email Id's and mobile numbers
   ArrayList<String> personNames=new ArrayList<>();
   ArrayList<String> emailIds=new ArrayList<>();
   ArrayList<String> mobileNumbers=new ArrayList<>();
   @Override
   protected void onCreate(Bundle savedInstanceState) {
      super.onCreate(savedInstanceState);
      setContentView(R.layout.activity_main);
      // get the reference of RecyclerView
      RecyclerView recyclerView=(RecyclerView) findViewById(R.id.recyclerView);
      // set a LinearLayoutManager with default vertical orientation
      LinearLayoutManager linearLayoutManager=new LinearLayoutManager(getApplicationContext());
      recyclerView.setLayoutManager(linearLayoutManager);
      try {
         // get JSONObject from JSON file
         JSONObject obj=new JSONObject(loadJSONFromAsset());
         // fetch JSONArray named users
         JSONArray userArray=obj.getJSONArray("users");
         // implement for loop for getting users list data
         for (int i = 0; i < userArray.length(); i++) {
            // create a JSONObject for fetching single user data
            JSONObject userDetail=userArray.getJSONObject(i);
            // fetch email and name and store it in arraylist
            personNames.add(userDetail.getString("name"));
            emailIds.add(userDetail.getString("email"));
            // create a object for getting contact data from JSONObject
            JSONObject contact=userDetail.getJSONObject("contact");
            // fetch mobile number and store it in arraylist
            mobileNumbers.add(contact.getString("mobile"));
         }
      } catch (JSONException e) {
         e.printStackTrace();
      }
      // call the constructor of CustomAdapter to send the reference and data to Adapter
      CustomAdapter customAdapter=new CustomAdapter(MainActivity.this, personNames, emailIds, mobileNumbers);
      recyclerView.setAdapter(customAdapter); // set the Adapter to RecyclerView
   }
   public String loadJSONFromAsset() {
      String json=null;
      try {
         InputStream is=getAssets().open("users_list.json");
         int size=is.available();
         byte[] buffer=new byte[size];
         is.read(buffer);
         is.close();
         json=new String(buffer, "UTF-8");
      } catch (IOException ex) {
         ex.printStackTrace();
         return null;
      }
      return json;
   }
}

ステップ6 −次の依存関係をsrc / CustomAdapter.java

package com.example.sample;
import android.content.Context;
import android.support.v7.widget.RecyclerView;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;
import android.widget.Toast;
import java.util.ArrayList;
public class CustomAdapter extends RecyclerView.Adapter<CustomAdapter.MyViewHolder> {
   ArrayList<String> personNames;
   ArrayList<String> emailIds;
   ArrayList<String> mobileNumbers;
   Context context;
   public CustomAdapter(Context context, ArrayList<String> personNames, ArrayList<String> emailIds, ArrayList<String> mobileNumbers) {
      this.context=context;
      this.personNames=personNames;
      this.emailIds=emailIds;
      this.mobileNumbers=mobileNumbers;
   }
   @Override
   public MyViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
      // infalte the item Layout
      View v=LayoutInflater.from(parent.getContext()).inflate(R.layout.rowlayout, parent, false);
      MyViewHolder vh=new MyViewHolder(v); // pass the view to View Holder
      return vh;
   }
   @Override
   public void onBindViewHolder(MyViewHolder holder, final int position) {
      // set the data in items
      holder.name.setText(personNames.get(position));
      holder.email.setText(emailIds.get(position));
      holder.mobileNo.setText(mobileNumbers.get(position));
      // implement setOnClickListener event on item view.
      holder.itemView.setOnClickListener(new View.OnClickListener() {
         @Override
         public void onClick(View view) {
            // display a toast with person name on item click
            Toast.makeText(context, personNames.get(position), Toast.LENGTH_SHORT).show();
         }
      });
   }
   @Override
   public int getItemCount() {
      return personNames.size();
   }
   public class MyViewHolder extends RecyclerView.ViewHolder {
      TextView name, email, mobileNo; // init the item view's
      public MyViewHolder(View itemView) {
         super(itemView);
         // get the reference of item view's
         name=(TextView) itemView.findViewById(R.id.tvName);
         email=(TextView) itemView.findViewById(R.id.tvEmail);
         mobileNo=(TextView) itemView.findViewById(R.id.tvMobile);
      }
   }
}

ステップ7 −次のコードをapp/manifests/AndroidManifest.xmlに追加します

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="https://schemas.android.com/apk/res/android"
   package="com.example.sample" >
   <application
      android:allowBackup="true"
      android:icon="@mipmap/ic_launcher"
      android:label="@string/app_name"
      android:roundIcon="@mipmap/ic_launcher_round"
      android:supportsRtl="true"
      android:theme="@style/AppTheme" >
      <activity android:name=".MainActivity" >
         <intent-filter>
            <action android:name="android.intent.action.MAIN" />
            <category android:name="android.intent.category.LAUNCHER" />
         </intent-filter>
      </activity>
   </application>
</manifest>