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

    <LinearLayout
        android:id="@+id/layout1"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:orientation="vertical">
        <TextView
            android:id="@+id/tv1"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:gravity="" />

        <EditText
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:id="@+id/et1"
            android:text="N"/>
        <LinearLayout
            android:layout_width="match_parent"
            android:layout_height="wrap_content">
           <TextView
               android:layout_width="wrap_content"
               android:layout_height="wrap_content"
               android:text="车号："/>
            <EditText
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:id="@+id/carCode"/>
        </LinearLayout>
    </LinearLayout>
</android.support.constraint.ConstraintLayout>

package com.example.meng.myapplication;

import android.app.PendingIntent;
import android.content.Context;
import android.content.Intent;
import android.content.IntentFilter;
import android.graphics.Color;
import android.nfc.NfcAdapter;
import android.nfc.Tag;
import android.nfc.tech.IsoDep;
import android.nfc.tech.MifareClassic;
import android.nfc.tech.NfcA;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.widget.EditText;
import android.widget.TextView;
import android.widget.Toast;


public class MainActivity extends AppCompatActivity {
    private IntentFilter mIntentFilter[];
    private Intent mIntent;
    private PendingIntent mPendingIntent;
    private NfcAdapter mNfcAdapter;
    private String[][] mTechLists;
    private EditText mSector;//扇区
    private EditText mCarCode;//车号


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        TextView tv = findViewById(R.id.tv1);
        mSector = findViewById(R.id.et1);
        mNfcAdapter = NfcAdapter.getDefaultAdapter(this);
        if (mNfcAdapter == null) {
            tv.setText("当前手机不支持NFC");
            return;
        } else if (!mNfcAdapter.isEnabled()) {
            tv.setText("手机支持NFC，请启动NFC功能");
            return;
        } else if (mNfcAdapter.isEnabled()) {
            tv.setText("已经开启NFC功能");

        } else {
            tv.setText("未知问题");
            return;
        }
        mIntent = new Intent(this, MainActivity.class).addFlags(Intent.FLAG_ACTIVITY_SINGLE_TOP);
        mPendingIntent = PendingIntent.getActivity(this, 0, mIntent, PendingIntent.FLAG_UPDATE_CURRENT);
        try {
            mIntentFilter = new IntentFilter[]{new IntentFilter(NfcAdapter.ACTION_TECH_DISCOVERED, "*/*")};
        } catch (Exception e) {
            e.printStackTrace();
        }
        mTechLists = new String[][]{new String[]{MifareClassic.class.getName()}, {IsoDep.class.getName()},{NfcA.class.getName()}};
    }

    @Override
    public void onNewIntent(Intent intent) {
        int i=Integer.parseInt(mSector.getText().toString());

        Tag tag = intent.getParcelableExtra(NfcAdapter.EXTRA_TAG);
        MifareClassic mifareClassic = MifareClassic.get(tag);
//        byte[] ids = tag.getId();
//        String str= bytes2HexString(ids);
        String str2 = "";

        //密码
        //byte[] bytes ="ffffffffffff".getBytes();//不好用
        //byte[] bytes={(byte)0xff,(byte)0xff,(byte)0xff,(byte)0xff,(byte)0xff,(byte)0xff};//
        //Toast.makeText(this, "OK", Toast.LENGTH_SHORT).show();

        try {
            mifareClassic.connect();
            //获取扇区数
            //str2 = mifareClassic.getSectorCount() + "";
            //获取总块数
            //str2 = mifareClassic.getBlockCount() + "";
            //验证密码
            boolean isOpen = mifareClassic.authenticateSectorWithKeyA(i, bytes);//MifareClassic.KEY_DEFAULT
            if (isOpen) {
                //String carCode = new String(mifareClassic.readBlock(n),"GB2312").replace("*","");//

　　　　　　  　　 mifareClassic.writeBlock(17,"津NMC110*********".getBytes("GB2312"));//写入-必须是16字节，gb2312中文占2个字节

 Toast.makeText(this, carCode, Toast.LENGTH_LONG).show(); return; }else { Toast.makeText(this, "密码错误", Toast.LENGTH_LONG).show(); return; } } catch (Exception e) { e.printStackTrace(); str2 = e.getMessage(); Toast.makeText(this, str2, Toast.LENGTH_LONG).show(); return; } finally { try { mifareClassic.close(); } catch (Exception e) { e.printStackTrace(); str2 = e.getMessage(); Toast.makeText(this, str2, Toast.LENGTH_LONG).show(); return; } } //Toast.makeText(this, str2, Toast.LENGTH_LONG).show();  } //  @Override public void onResume() { super.onResume(); //设置处理优于所有其他NFC的处理 if (mNfcAdapter != null) mNfcAdapter.enableForegroundDispatch(this, mPendingIntent, mIntentFilter, mTechLists); } //暂停Activity，界面获取焦点  @Override public void onPause() { super.onPause(); //  if (mNfcAdapter != null) mNfcAdapter.disableForegroundDispatch(this); } }