android nfc(官方翻譯)

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To filter for ACTION_TAG_DISCOVERED use the following intent filter:

Obtaining information from intents

If an activity starts because of an NFC intent, you can obtain information about the scanned NFC tag from the intent. Intents can contain the following extras depending on the tag that was scanned:

如果由於一個NFC的Intent啟動的Activity，你可以通過從被掃描到的intent獲取信息，被掃描的intent可以包含如下extras：

EXTRA_TAG (required): A Tag object representing the scanned tag.
EXTRA_NDEF_MESSAGES (optional): An array of NDEF messages parsed from the tag. This extra is mandatory on intents.
{@link android.nfc.NfcAdapter#EXTRA_ID (optional): The low-level ID of the tag.

To obtain these extras, check to see if your activity was launched with one of the NFC intents to ensure that a tag was scanned, and then obtain the extras out of the intent. The following example checks for the ACTION_NDEF_DISCOVERED intent and gets the NDEF messages from an intent extra.

為了獲取這些extras，檢測你的Activity通過一個NFC intent被發起以確保一個標簽被掃描到，然後從intent獲取extras，如下例子檢測ACTION_NDEF_DISCOVERED的intent然後從intent extra中獲取NDEF messages。

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
}

另外，你可以獲取一個標簽對象，並從標簽對象上可以獲取payload並且允許你枚舉出所有的tag's technologies

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

This section describes how to create common types of NDEF records to help you when writing to NFC tags or sending data with Android Beam. Starting with Android 4.0 (API level 14), the createUri() method is available to help you create URI records automatically. Starting in Android 4.1 (API level 16), createExternal() and createMime() are available to help you create MIME and external type NDEF records. Use these helper methods whenever possible to avoid mistakes when manually creating NDEF records.
這部分描述了創建公共的NDEF records當你需要寫標簽或發送數據到給一個Android Beam，從Android 4.0 (API level 14)起createUri()是可用的幫助你自動創建URI records，從Android 4.1 (API level 16)起createExternal() and createMime()是可用的幫助你創建MIME and external type NDEF records，使用幫助方法盡可能來避免因為手動創建NDEF records時出現錯誤

This section also describes how to create the corresponding intent filter for the record. All of these NDEF record examples should be in the first NDEF record of the NDEF message that you are writing to a tag or beaming.

這部分描述了如何創建對應 intent filter對應的record，所有這些NDEF record 例子都應該在你寫標簽或者beaming的NDEF message的第一個NDEF record

TNF_ABSOLUTE_URI：

Note: We recommend that you use the RTD_URI type instead of TNF_ABSOLUTE_URI, because it is more efficient.

建議使用RTD_URI替代TNF_ABSOLUTE_URI

You can create a TNF_ABSOLUTE_URI NDEF record in the following way:

NdefRecord uriRecord = new NdefRecord(
    NdefRecord.TNF_ABSOLUTE_URI ,
    "http://developer.android.com/index.html".getBytes(Charset.forName("US-ASCII")),
    new byte[0], new byte[0]);

You can create a TNF_MIME_MEDIA NDEF record in the following ways.

Using the createMime() method:

NdefRecord mimeRecord = NdefRecord.createMime("application/vnd.com.example.android.beam",
    "Beam me up, Android".getBytes(Charset.forName("US-ASCII")));

NdefRecord mimeRecord = new NdefRecord(
    NdefRecord.TNF_MIME_MEDIA ,
    "application/vnd.com.example.android.beam".getBytes(Charset.forName("US-ASCII")),
    new byte[0], "Beam me up, Android!".getBytes(Charset.forName("US-ASCII")));

You can create a TNF_WELL_KNOWN NDEF record in the following way:

public NdefRecord createTextRecord(String payload, Locale locale, boolean encodeInUtf8) {
    byte[] langBytes = locale.getLanguage().getBytes(Charset.forName("US-ASCII"));
    Charset utfEncoding = encodeInUtf8 ? Charset.forName("UTF-8") : Charset.forName("UTF-16");
    byte[] textBytes = payload.getBytes(utfEncoding);
    int utfBit = encodeInUtf8 ? 0 : (1 << 7);
    char status = (char) (utfBit + langBytes.length);
    byte[] data = new byte[1 + langBytes.length + textBytes.length];
    data[0] = (byte) status;
    System.arraycopy(langBytes, 0, data, 1, langBytes.length);
    System.arraycopy(textBytes, 0, data, 1 + langBytes.length, textBytes.length);
    NdefRecord record = new NdefRecord(NdefRecord.TNF_WELL_KNOWN,
    NdefRecord.RTD_TEXT, new byte[0], data);
    return record;
}

You can create a TNF_WELL_KNOWN NDEF record in the following ways.

Using the createUri(String) method:

NdefRecord rtdUriRecord1 = NdefRecord.createUri("http://example.com");

Uri uri = new Uri("http://example.com");
NdefRecord rtdUriRecord2 = NdefRecord.createUri(uri);

byte[] uriField = "example.com".getBytes(Charset.forName("US-ASCII"));
byte[] payload = new byte[uriField.length + 1];              //add 1 for the URI Prefix
byte payload[0] = 0x01;                                      //prefixes http://www. to the URI
System.arraycopy(uriField, 0, payload, 1, uriField.length);  //appends URI to payload
NdefRecord rtdUriRecord = new NdefRecord(
    NdefRecord.TNF_WELL_KNOWN, NdefRecord.RTD_URI, new byte[0], payload);

You can create a TNF_EXTERNAL_TYPE NDEF record in the following ways:

Using the createExternal() method:

byte[] payload; //assign to your data
String domain = "com.example"; //usually your app's package name
String type = "externalType";
NdefRecord extRecord = NdefRecord.createExternal(domain, type, payload);

byte[] payload;
...
NdefRecord extRecord = new NdefRecord(
    NdefRecord.TNF_EXTERNAL_TYPE, "com.example:externalType", new byte[0], payload);

Note: URNs for TNF_EXTERNAL_TYPE have a canonical format of: urn:nfc:ext:example.com:externalType, however the NFC Forum RTD specification declares that the urn:nfc:ext: portion of the URN must be ommitted from the NDEF record. So all you need to provide is the domain (example.com in the example) and type (externalType in the example) separated by a colon. When dispatching TNF_EXTERNAL_TYPE, Android converts the urn:nfc:ext:example.com:externalType URN to a vnd.android.nfc://ext/example.com:externalType URI, which is what the intent filter in the example declares.

Android Application Records

Introduced in Android 4.0 (API level 14), an Android Application Record (AAR) provides a stronger certainty that your application is started when an NFC tag is scanned. An AAR has the package name of an application embedded inside an NDEF record. You can add an AAR to any NDEF record of your NDEF message, because Android searches the entire NDEF message for AARs. If it finds an AAR, it starts the application based on the package name inside the AAR. If the application is not present on the device, Google Play is launched to download the application.

Android 4.0 (API level 14)引進的，一個Android Application Record (AAR)提供了更強的功能，當你的NFC標簽被掃描會啟動你的應用，一個AAR由一個應用的包名被嵌入在NDEF record。你能增加一個AAR到NDEF裡任何一個NDEF record因為Android搜索全部NDEF message中的AAR，如果找到了AAR，它就啟動AAR中包名對應的應用，如果應用不存在你的設備中，Google Play會被發起來下載對應的應用。

AARs are useful if you want to prevent other applications from filtering for the same intent and potentially handling specific tags that you have deployed. AARs are only supported at the application level, because of the package name constraint, and not at the Activity level as with intent filtering. If you want to handle an intent at the Activity level, use intent filters.

AAR是有用的對於你想防止其他應用過濾相同的intent，和其他應用處理你部署的具體的標簽，因為AARs僅僅支持應用水平（由包名常量指定），不能被過濾由其他的應用通過intent filtering，如果你想處理一個intent在Activity水平，使用intent filters。

If a tag contains an AAR, the tag dispatch system dispatches in the following manner:

如果一個標簽包含一個AAR，標簽調度系統采用如下方式進行調度：

1.Try to start an Activity using an intent filter as normal. If the Activity that matches the intent also matches the AAR, start the Activity.

試圖使用intent filter啟動一個Activity正常情況下，如果由intent匹配的Activity也匹配AAR，啟動Activity

2.If the Activity that filters for the intent does not match the AAR, if multiple Activities can handle the intent, or if no Activity handles the intent, start the application specified by the AAR.
如果filter過濾的intent對應的Activity不匹配AAR，如果多個Activity能處理intent，或者沒有應用能處理intent，啟動由AAR具體指定的應用

3.If no application can start with the AAR, go to Google Play to download the application based on the AAR.
如果沒有AAR所指定的應用，將打開Google Play下載AAR指定的應用

Android provides a simple API to create an AAR, createApplicationRecord(). All you need to do is embed the AAR anywhere in your NdefMessage. You do not want to use the first record of your NdefMessage, unless the AAR is the only record in the NdefMessage. This is because the Android system checks the first record of an NdefMessage to determine the MIME type or URI of the tag, which is used to create an intent for applications to filter. The following code shows you how to create an AAR:

android提供了一個簡單的api，createApplicationRecord()創建AAR，你需要嵌入AAR在任何NdefMessage，你應該使用NdefMessage中的第一個record，除非NdefMessage只有一個record，因為android系統檢查NdefMessage第一個record決定標簽的MIME類型或者URI，那用來創建一個intent為應用來過濾，下面代碼教你如何創建一個AAR：

NdefMessage msg = new NdefMessage(
        new NdefRecord[] {
            ...,
            NdefRecord.createApplicationRecord("com.example.android.beam")}