Android中NFC功能流程圖解析及代碼演示

Colin收藏 2012-05-24

展開全文

在Android4.0推出的時候，一個非常引人注目的功能就是NFC(Near Field Communication).

Near Field Communication (NFC) is a set of short-range wireless technologies, typically requiring a distance of 4cm or less to initiate a connection. NFC allows you to share small payloads of data between an NFC tag and an Android-powered device, or between two Android-powered devices.

翻譯：
近場通訊(NFC)是一系列短距離無線技術，一般需要4cm或者更短去初始化連接。近場通訊(NFC)允許你在NFC tag和Android設備或者兩個Android設備間共享小負載數(shù)據(jù)。
典型的應用為刷卡應用，如刷信用卡，公交車卡，吃飯的飯卡之類。騰訊2011年1月份文章“Android首款NFC近場通信應用推出”，說明了基于Android的NFC應用目前已經(jīng)有了，得益于日本在手機刷卡的應用氛圍。據(jù)2011年7月網(wǎng)易文章“PayPal推出Android系統(tǒng)NFC移動支付服務”報道，PayPal已經(jīng)做了嘗試了，相信這股風很快要刮到中國。

下面我們從技術的層面來分析一下這個技術。

官方的圖片示例為：

這是NFC的開發(fā)流程，參考文章 “【NFC在android中的應用API】”。
相關的類代碼有：NfcAdapter,NdefMessage, NdefRecord,ACTION_TAG_DISCOVERED.
在功能層面上，涉及到了NFC的讀寫功能。下面我們分別來做總結(jié)。
在代碼層上面：
使用的時候，需要在AndroidManifest.xml里面加一些權限以及屬性。

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01 02 03	`<uses-permission android:name="android.permission.NFC"/>` `<uses-feature android:name="android.hardware.nfc"` `android:required="true"/>` `<uses-sdk android:minSdkVersion="10"/>`

這里注意，在Android Version 9的時候僅僅支持了ACTION_TAG_DISCOVERED，對于其他的需要10以上。
在上面的基礎上，還需要增加intent-filter的支持。

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01 02 03 04	`<intent-filter>` `<action android:name="android.nfc.action.NDEF_DISCOVERED"/>` `<category android:name="android.intent.category.DEFAULT"/>` `<data android:mimeType="text/plain"/></intent-filter>`

獲取NfcAdapter的代碼為

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01 02 03 04 05 06 07 08 09 10 11	`public` `static` `String getStatusNfcDevice () {` `NfcAdapter nfcAdapter = NfcAdapter.getDefaultAdapter();` `if` `(nfcAdapter.isEnabled()) {` `String status =` `"enabled";` `return` `status;` `}` `else` `{` `String status =` `"disabled";` `return` `status;` `}` `}`

處理函數(shù)為

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01 02 03 04 05 06 07 08 09 10 11 12 13	`public` `void` `onResume() {` `super.onResume();` `if` `(NfcAdapter.ACTION_NDEF_DISCOVERED.equals(getIntent().getAction())) {` `Parcelable[] rawMsgs = intent.getParcelableArrayExtra(NfcAdapter.EXTRA_NDEF_MESSAGES);` `if` `(rawMsgs !=` `null) {` `msgs =` `new` `NdefMessage[rawMsgs.length];` `for` `(int` `i =` `0; i < rawMsgs.length; i++) {` `msgs<i> = (NdefMessage) rawMsgs<i>;` `}` `}` `}` `//process the msgs array` `}</i></i>`

完整的一個操作代碼摘自Google Android NFC Guide代碼（略加注釋）：

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package com.example.android.beam;

import android.app.Activity;

import android.content.Intent;

import android.nfc.NdefMessage;

import android.nfc.NdefRecord;

import android.nfc.NfcAdapter;

import android.nfc.NfcAdapter.CreateNdefMessageCallback;

import android.nfc.NfcEvent;

import android.os.Bundle;

import android.os.Parcelable;

import android.widget.TextView;

import android.widget.Toast;

import java.nio.charset.Charset;

//繼承并實現(xiàn)接口CreateNdefMessageCallback方法createNdefMessage

public class Beam extends Activity implements CreateNdefMessageCallback {

NfcAdapter mNfcAdapter;

TextView textView;

@Override

public void onCreate(Bundle savedInstanceState) {

super.onCreate(savedInstanceState);

setContentView(R.layout.main);

TextView textView = (TextView) findViewById(R.id.textView);

// Check for available NFC Adapter

//檢測是否有NFC適配器

mNfcAdapter = NfcAdapter.getDefaultAdapter(this);

if (mNfcAdapter == null) {

Toast.makeText(this, "NFC is not available", Toast.LENGTH_LONG).show();

finish();

return;

}

// Register callback

//注冊回調(diào)函數(shù)

mNfcAdapter.setNdefPushMessageCallback(this, this);

}

@Override

public NdefMessage createNdefMessage(NfcEvent event) {

String text = ("Beam me up, Android!\n\n" +

"Beam Time: " + System.currentTimeMillis());

//回調(diào)函數(shù)，構(gòu)造NdefMessage格式

NdefMessage msg = new NdefMessage(

new NdefRecord[] { createMimeRecord(

"application/com.example.android.beam", text.getBytes())

/**

* The Android Application Record (AAR) is commented out. When a device

* receives a push with an AAR in it, the application specified in the AAR

* is guaranteed to run. The AAR overrides the tag dispatch system.

* You can add it back in to guarantee that this

* activity starts when receiving a beamed message. For now, this code

* uses the tag dispatch system.

*/

//,NdefRecord.createApplicationRecord("com.example.android.beam")

});

return msg;

}

@Override

public void onResume() {

super.onResume();

// Check to see that the Activity started due to an Android Beam

//得到是否檢測到ACTION_NDEF_DISCOVERED觸發(fā)

if (NfcAdapter.ACTION_NDEF_DISCOVERED.equals(getIntent().getAction())) {

processIntent(getIntent());

}

}

//重載Activity類方法處理當新Intent到來事件

@Override

public void onNewIntent(Intent intent) {

// onResume gets called after this to handle the intent

setIntent(intent);

}

/**

* Parses the NDEF Message from the intent and prints to the TextView

*/

//關鍵處理函數(shù)，處理掃描到的NdefMessage

void processIntent(Intent intent) {

textView = (TextView) findViewById(R.id.textView);

Parcelable[] rawMsgs = intent.getParcelableArrayExtra(

NfcAdapter.EXTRA_NDEF_MESSAGES);

// only one message sent during the beam

NdefMessage msg = (NdefMessage) rawMsgs[0];

// record 0 contains the MIME type, record 1 is the AAR, if present

textView.setText(new String(msg.getRecords()[0].getPayload()));

}

/**

* Creates a custom MIME type encapsulated in an NDEF record

*/

public NdefRecord createMimeRecord(String mimeType, byte[] payload) {

byte[] mimeBytes = mimeType.getBytes(Charset.forName("US-ASCII"));

NdefRecord mimeRecord = new NdefRecord(

NdefRecord.TNF_MIME_MEDIA, mimeBytes, new byte[0], payload);

return mimeRecord;

}

}

上面代碼還需要在AndroidManifest.xml文件里面添加
<intent-filter>
  < action android:name="android.nfc.action.NDEF_DISCOVERED"/>
  < category android:name="android.intent.category.DEFAULT"/>
  < data android:mimeType="application/com.example.android.beam"/>
< /intent-filter>

在對NFC設備進行寫操作的時候，相關代碼:

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private void enableTagWriteMode() {

mWriteMode = true;

IntentFilter tagDetected = new IntentFilter(NfcAdapter.ACTION_TAG_DISCOVERED);

mWriteTagFilters = new IntentFilter[] { tagDetected };

mNfcAdapter.enableForegroundDispatch(this, mNfcPendingIntent, mWriteTagFilters, null);

}

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@Override

protected void onNewIntent(Intent intent) {

// Tag writing mode

if (mWriteMode && NfcAdapter.ACTION_TAG_DISCOVERED.equals(intent.getAction())) {

Tag detectedTag = intent.getParcelableExtra(NfcAdapter.EXTRA_TAG);

if (NfcUtils.writeTag(NfcUtils.getPlaceidAsNdef(placeidToWrite), detectedTag)) {

Toast.makeText(this, "Success: Wrote placeid to nfc tag", Toast.LENGTH_LONG)

.show();

NfcUtils.soundNotify(this);

} else {

Toast.makeText(this, "Write failed", Toast.LENGTH_LONG).show();

}

}

}

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/*

* Writes an NdefMessage to a NFC tag

*/

public static boolean writeTag(NdefMessage message, Tag tag) {

int size = message.toByteArray().length;

try {

Ndef ndef = Ndef.get(tag);

if (ndef != null) {

ndef.connect();

if (!ndef.isWritable()) {

return false;

}

if (ndef.getMaxSize() < size) {

return false;

}

ndef.writeNdefMessage(message);

return true;

} else {

NdefFormatable format = NdefFormatable.get(tag);

if (format != null) {

try {

format.connect();

format.format(message);

return true;

} catch (IOException e) {

return false;

}

} else {

return false;

}

}

} catch (Exception e) {

return false;

}

}

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<activity android:name=".CheckInActivity">

<intent-filter>

<action android:name="android.nfc.action.NDEF_DISCOVERED"/>

<data android:mimeType="application/vnd.facebook.places"/>

<category android:name="android.intent.category.DEFAULT"/>

</intent-filter>

</activity>