package com.example.nfctest;

import android.app.PendingIntent;
import android.content.Intent;
import android.nfc.NdefMessage;
import android.nfc.NfcAdapter;
import android.nfc.Tag;
import android.os.Parcelable;
import android.provider.Settings;
import android.util.Log;
import android.widget.Toast;

import androidx.appcompat.app.AppCompatActivity;

public class BaseNfcActivity extends AppCompatActivity {

    private NfcAdapter mNfcAdapter;
    private PendingIntent mPendingIntent;
    @Override
    protected void onStart() {
        super.onStart();
        mNfcAdapter= NfcAdapter.getDefaultAdapter(this);//设备的NfcAdapter对象
        if(mNfcAdapter==null){//判断设备是否支持NFC功能
            Toast.makeText(this,"设备不支持NFC功能!",Toast.LENGTH_SHORT);
            finish();
            return;
        }
        if (!mNfcAdapter.isEnabled()){//判断设备NFC功能是否打开
            Toast.makeText(this,"请到系统设置中打开NFC功能!",Toast.LENGTH_SHORT);
            finish();
            return;
        }
        mPendingIntent= PendingIntent.getActivity(this,0,new Intent(this,getClass()).addFlags(Intent.FLAG_ACTIVITY_SINGLE_TOP),0);//创建PendingIntent对象,当检测到一个Tag标签就会执行此Intent
        Log.d("myNFC","NFC is start");
    }

    //页面获取焦点
    @Override
    protected void onResume() {
        super.onResume();
        if (mNfcAdapter!=null){
            mNfcAdapter.enableForegroundDispatch(this,mPendingIntent,null,null);//打开前台发布系统，使页面优于其它nfc处理.当检测到一个Tag标签就会执行mPendingItent
            Log.d("myNFC","onResume");
        }
    }

    //页面失去焦点
    @Override
    protected void onPause() {
        super.onPause();
        if(mNfcAdapter!=null){
            mNfcAdapter.disableForegroundDispatch(this);//关闭前台发布系统
        }
    }
    
	//也是工具不过我没用上。
    public static String flipHexStr(String s) {
        StringBuilder result = new StringBuilder();
        for (int i = 0; i <= s.length() - 2; i = i + 2) {
            result.append(new StringBuilder(s.substring(i, i + 2)).reverse());
        }
        return result.reverse().toString();
    }
    
	//工具，十六进制转十进制用的
    String ByteArrayToHexString(byte[] inarray) {
        int i, j, in;
        String[] hex = { "0", "1", "2", "3", "4", "5", "6", "7", "8", "9", "A",
                "B", "C", "D", "E", "F" };
        String out = "";

        for (j = 0; j < inarray.length; ++j) {
            in = (int) inarray[j] & 0xff;
            i = (in >> 4) & 0x0f;
            out += hex[i];
            i = in & 0x0f;
            out += hex[i];
        }
        return out;
    }
}

然后就是MainActivity.java，让它继承刚刚写的BaseNfcActivity。

package com.example.nfctest;

import android.content.Intent;
import android.nfc.NdefMessage;
import android.nfc.NfcAdapter;
import android.nfc.Tag;
import android.os.Bundle;
import android.os.Parcelable;
import android.util.Log;
import android.widget.TextView;

public class MainActivity extends BaseNfcActivity {
    TextView content;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        content = findViewById(R.id.content);
    }


    @Override
    protected void onNewIntent(Intent intent) {
        super.onNewIntent(intent);
        if(NfcAdapter.ACTION_TAG_DISCOVERED.equals(intent.getAction())){
            Tag tag = intent.getParcelableExtra(NfcAdapter.EXTRA_TAG);
//            Long cardId = Long.parseLong(flipHexStr(ByteArrayToHexString(tag.getId())), 16);
//            Long cardId = Long.parseLong(ByteArrayToHexString(tag.getId()), 16);
            String cardId = ByteArrayToHexString(tag.getId());
            content.setText(cardId.toString());
        }
        Log.d("myNFC",intent.toString());
    }
}

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.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:layout_width="match_parent"
        android:layout_height="match_parent"
        android:id="@+id/content"
        />

</androidx.constraintlayout.widget.ConstraintLayout>