1年に1回くらいAndroidでNFC（FeliCa）をいじる人間のメモ（2019年初夏）

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="jp.bluecode.buttontest">

    <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>

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

</manifest>

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

    <TextView
        android:id="@+id/txt01"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginTop="8dp"
        android:text="Read ID ..."
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintVertical_bias="0.308" />

    <Button
        android:id="@+id/btn01"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text=" Reader Mode On"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.498"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/txt01"
        app:layout_constraintVertical_bias="0.107" />

    <Button
        android:id="@+id/btn02"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Reader Mode Off"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.498"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/btn01"
        app:layout_constraintVertical_bias="0.116" />

</android.support.constraint.ConstraintLayout>

package jp.bluecode.buttontest;

import android.nfc.NfcAdapter;
import android.nfc.Tag;
import android.os.Handler;
import android.os.Looper;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;

import java.util.Formatter;
import java.util.Locale;

public class MainActivity extends AppCompatActivity {

    //Viewで使う変数を初期化（別にここじゃなくてもいいけど）
    TextView txt01;
    Button btn01;
    Button btn02;

    //NfcAdapterを初期化
    NfcAdapter nfcAdapter;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        //UIのマーツをマッピング
        txt01 = findViewById(R.id.txt01);
        btn01 = findViewById(R.id.btn01);
        btn02 = findViewById(R.id.btn02);

        //nfcAdapter初期化
        nfcAdapter = NfcAdapter.getDefaultAdapter(this);

        //Reader Mode Offボタンのenabledをfalseに（トグルにするため）
        btn02.setEnabled(false);

        btn01.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                //トグル機能
                btn01.setEnabled(false);
                btn02.setEnabled(true);

                //Redermode On
                nfcAdapter.enableReaderMode(MainActivity.this,new MyReaderCallback(),NfcAdapter.FLAG_READER_NFC_F,null);
            }
        });

        btn02.setOnClickListener(new View.OnClickListener(){
            @Override
            public void onClick(View v) {
                //トグル機能
                btn01.setEnabled(true);
                btn02.setEnabled(false);

                //Readermode Off
                nfcAdapter.disableReaderMode(MainActivity.this);

                //表示初期化
                txt01.setText("Read ID ...");
            }
        });
    }

    //Callback Class
    private class MyReaderCallback implements NfcAdapter.ReaderCallback{
        @Override
        public void onTagDiscovered(Tag tag){

            Log.d("Hoge","Tag discoverd.");

            //get idm
            byte[] idm = tag.getId();
            final String idmString = bytesToHexString(idm);

            //idm取るだけじゃなくてread,writeしたい場合はtag利用してごにょごにょする

            //親スレッドのUIを更新するためごにょごにょ
            final Handler mainHandler = new Handler(Looper.getMainLooper());
            mainHandler.post(new Runnable() {
                @Override
                public void run() {
                    txt01.setText(idmString);
                }
            });

        }
    }

    //bytes列を16進数文字列に変換（めんどい）
    public static String bytesToHexString(byte[] bytes) {
        StringBuilder sb = new StringBuilder();

        Formatter formatter = new Formatter(sb);
        for (byte b : bytes) {
            formatter.format("%02x", b);
        }

        return sb.toString().toUpperCase(Locale.getDefault());
    }
}