android/android-9.0.0_r35 : android/nfc/Tag.java

https://source.android.com/
/*
 * Copyright (C) 2010 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package android.nfc;

import android.content.Context;
import android.nfc.tech.IsoDep;
import android.nfc.tech.MifareClassic;
import android.nfc.tech.MifareUltralight;
import android.nfc.tech.Ndef;
import android.nfc.tech.NdefFormatable;
import android.nfc.tech.NfcA;
import android.nfc.tech.NfcB;
import android.nfc.tech.NfcBarcode;
import android.nfc.tech.NfcF;
import android.nfc.tech.NfcV;
import android.nfc.tech.TagTechnology;
import android.os.Bundle;
import android.os.Parcel;
import android.os.Parcelable;
import android.os.RemoteException;

import java.io.IOException;
import java.util.Arrays;
import java.util.HashMap;

Represents an NFC tag that has been discovered.
 Tag is an immutable object that represents the state of a NFC tag at the time of discovery. It can be used as a handle to TagTechnology classes to perform advanced operations, or directly queried for its ID via getId and the set of technologies it contains via getTechList. Arrays passed to and returned by this class are not cloned, so be careful not to modify them.
 A new tag object is created every time a tag is discovered (comes into range), even if it is the same physical tag. If a tag is removed and then returned into range, then only the most recent tag object can be successfully used to create a TagTechnology. 
Tag Dispatch
 When a tag is discovered, a Tag object is created and passed to a single activity via the NfcAdapter.EXTRA_TAG extra in an Intent via Context.startActivity. A four stage dispatch is used to select the most appropriate activity to handle the tag. The Android OS executes each stage in order, and completes dispatch as soon as a single matching activity is found. If there are multiple matching activities found at any one stage then the Android activity chooser dialog is shown to allow the user to select the activity to receive the tag. The Tag dispatch mechanism was designed to give a high probability of dispatching
a tag to the correct activity without showing the user an activity chooser dialog.
This is important for NFC interactions because they are very transient -- if a user has to
move the Android device to choose an application then the connection will likely be broken.
1. Foreground activity dispatch
 A foreground activity that has called NfcAdapter.enableForegroundDispatch() is given priority. See the documentation on NfcAdapter.enableForegroundDispatch() for its usage. 2. NDEF data dispatch
 If the tag contains NDEF data the system inspects the first NdefRecord in the first NdefMessage. If the record is a URI, SmartPoster, or MIME data Context.startActivity is called with NfcAdapter.ACTION_NDEF_DISCOVERED. For URI and SmartPoster records the URI is put into the intent's data field. For MIME records the MIME type is put in the intent's type field. This allows activities to register to be launched only when data they know how to handle is present on a tag. This is the preferred method of handling data on a tag since NDEF data can be stored on many types of tags and doesn't depend on a specific tag technology. See NfcAdapter.ACTION_NDEF_DISCOVERED for more detail. If the tag does not contain NDEF data, or if no activity is registered for NfcAdapter.ACTION_NDEF_DISCOVERED with a matching data URI or MIME type then dispatch moves to stage 3. 3. Tag Technology dispatch
 Context.startActivity is called with NfcAdapter.ACTION_TECH_DISCOVERED to dispatch the tag to an activity that can handle the technologies present on the tag. Technologies are defined as sub-classes of TagTechnology, see the package tech. The Android OS looks for an activity that can handle one or more technologies in the tag. See NfcAdapter.ACTION_TECH_DISCOVERED for more detail. 4. Fall-back dispatch
 If no activity has been matched then Context.startActivity is called with NfcAdapter.ACTION_TAG_DISCOVERED. This is intended as a fall-back mechanism. See NfcAdapter.ACTION_TAG_DISCOVERED. NFC Tag Background
An NFC tag is a passive NFC device, powered by the NFC field of this Android device while
it is in range. Tag's can come in many forms, such as stickers, cards, key fobs, or
even embedded in a more sophisticated device.
 Tags can have a wide range of capabilities. Simple tags just offer read/write semantics, and contain some one time programmable areas to make read-only. More complex tags offer math operations and per-sector access control and authentication. The most sophisticated tags contain operating environments allowing complex interactions with the code executing on the tag. Use TagTechnology classes to access a broad range of capabilities available in NFC tags. 

/**
 * Represents an NFC tag that has been discovered.
 * <p>
 * {@link Tag} is an immutable object that represents the state of a NFC tag at
 * the time of discovery. It can be used as a handle to {@link TagTechnology} classes
 * to perform advanced operations, or directly queried for its ID via {@link #getId} and the
 * set of technologies it contains via {@link #getTechList}. Arrays passed to and
 * returned by this class are <em>not</em> cloned, so be careful not to modify them.
 * <p>
 * A new tag object is created every time a tag is discovered (comes into range), even
 * if it is the same physical tag. If a tag is removed and then returned into range, then
 * only the most recent tag object can be successfully used to create a {@link TagTechnology}.
 *
 * <h3>Tag Dispatch</h3>
 * When a tag is discovered, a {@link Tag} object is created and passed to a
 * single activity via the {@link NfcAdapter#EXTRA_TAG} extra in an
 * {@link android.content.Intent} via {@link Context#startActivity}. A four stage dispatch is used
 * to select the
 * most appropriate activity to handle the tag. The Android OS executes each stage in order,
 * and completes dispatch as soon as a single matching activity is found. If there are multiple
 * matching activities found at any one stage then the Android activity chooser dialog is shown
 * to allow the user to select the activity to receive the tag.
 *
 * <p>The Tag dispatch mechanism was designed to give a high probability of dispatching
 * a tag to the correct activity without showing the user an activity chooser dialog.
 * This is important for NFC interactions because they are very transient -- if a user has to
 * move the Android device to choose an application then the connection will likely be broken.
 *
 * <h4>1. Foreground activity dispatch</h4>
 * A foreground activity that has called
 * {@link NfcAdapter#enableForegroundDispatch NfcAdapter.enableForegroundDispatch()} is
 * given priority. See the documentation on
 * {@link NfcAdapter#enableForegroundDispatch NfcAdapter.enableForegroundDispatch()} for
 * its usage.
 * <h4>2. NDEF data dispatch</h4>
 * If the tag contains NDEF data the system inspects the first {@link NdefRecord} in the first
 * {@link NdefMessage}. If the record is a URI, SmartPoster, or MIME data
 * {@link Context#startActivity} is called with {@link NfcAdapter#ACTION_NDEF_DISCOVERED}. For URI
 * and SmartPoster records the URI is put into the intent's data field. For MIME records the MIME
 * type is put in the intent's type field. This allows activities to register to be launched only
 * when data they know how to handle is present on a tag. This is the preferred method of handling
 * data on a tag since NDEF data can be stored on many types of tags and doesn't depend on a
 * specific tag technology. 
 * See {@link NfcAdapter#ACTION_NDEF_DISCOVERED} for more detail. If the tag does not contain
 * NDEF data, or if no activity is registered
 * for {@link NfcAdapter#ACTION_NDEF_DISCOVERED} with a matching data URI or MIME type then dispatch
 * moves to stage 3.
 * <h4>3. Tag Technology dispatch</h4>
 * {@link Context#startActivity} is called with {@link NfcAdapter#ACTION_TECH_DISCOVERED} to
 * dispatch the tag to an activity that can handle the technologies present on the tag.
 * Technologies are defined as sub-classes of {@link TagTechnology}, see the package
 * {@link android.nfc.tech}. The Android OS looks for an activity that can handle one or
 * more technologies in the tag. See {@link NfcAdapter#ACTION_TECH_DISCOVERED} for more detail.
 * <h4>4. Fall-back dispatch</h4>
 * If no activity has been matched then {@link Context#startActivity} is called with
 * {@link NfcAdapter#ACTION_TAG_DISCOVERED}. This is intended as a fall-back mechanism.
 * See {@link NfcAdapter#ACTION_TAG_DISCOVERED}.
 *
 * <h3>NFC Tag Background</h3>
 * An NFC tag is a passive NFC device, powered by the NFC field of this Android device while
 * it is in range. Tag's can come in many forms, such as stickers, cards, key fobs, or
 * even embedded in a more sophisticated device.
 * <p>
 * Tags can have a wide range of capabilities. Simple tags just offer read/write semantics,
 * and contain some one time
 * programmable areas to make read-only. More complex tags offer math operations
 * and per-sector access control and authentication. The most sophisticated tags
 * contain operating environments allowing complex interactions with the
 * code executing on the tag. Use {@link TagTechnology} classes to access a broad
 * range of capabilities available in NFC tags.
 * <p>
 */
public final class Tag implements Parcelable {
    final byte[] mId;
    final int[] mTechList;
    final String[] mTechStringList;
    final Bundle[] mTechExtras;
    final int mServiceHandle;  // for use by NFC service, 0 indicates a mock
    final INfcTag mTagService; // interface to NFC service, will be null if mock tag

    int mConnectedTechnology;

    Hidden constructor to be used by NFC service and internal classes.
@hide /**
     * Hidden constructor to be used by NFC service and internal classes.
     * @hide
     */
    public Tag(byte[] id, int[] techList, Bundle[] techListExtras, int serviceHandle,
            INfcTag tagService) {
        if (techList == null) {
            throw new IllegalArgumentException("rawTargets cannot be null");
        }
        mId = id;
        mTechList = Arrays.copyOf(techList, techList.length);
        mTechStringList = generateTechStringList(techList);
        // Ensure mTechExtras is as long as mTechList
        mTechExtras = Arrays.copyOf(techListExtras, techList.length);
        mServiceHandle = serviceHandle;
        mTagService = tagService;

        mConnectedTechnology = -1;
    }

    Construct a mock Tag.
This is an application constructed tag, so NfcAdapter methods on this Tag may fail with IllegalArgumentException since it does not represent a physical Tag. 
This constructor might be useful for mock testing.
Params: id – The tag identifier, can be null
techList – must not be null
Returns: freshly constructed tag
@hide /**
     * Construct a mock Tag.
     * <p>This is an application constructed tag, so NfcAdapter methods on this Tag may fail
     * with {@link IllegalArgumentException} since it does not represent a physical Tag.
     * <p>This constructor might be useful for mock testing.
     * @param id The tag identifier, can be null
     * @param techList must not be null
     * @return freshly constructed tag
     * @hide
     */
    public static Tag createMockTag(byte[] id, int[] techList, Bundle[] techListExtras) {
        // set serviceHandle to 0 and tagService to null to indicate mock tag
        return new Tag(id, techList, techListExtras, 0, null);
    }

    private String[] generateTechStringList(int[] techList) {
        final int size = techList.length;
        String[] strings = new String[size];
        for (int i = 0; i < size; i++) {
            switch (techList[i]) {
                case TagTechnology.ISO_DEP:
                    strings[i] = IsoDep.class.getName();
                    break;
                case TagTechnology.MIFARE_CLASSIC:
                    strings[i] = MifareClassic.class.getName();
                    break;
                case TagTechnology.MIFARE_ULTRALIGHT:
                    strings[i] = MifareUltralight.class.getName();
                    break;
                case TagTechnology.NDEF:
                    strings[i] = Ndef.class.getName();
                    break;
                case TagTechnology.NDEF_FORMATABLE:
                    strings[i] = NdefFormatable.class.getName();
                    break;
                case TagTechnology.NFC_A:
                    strings[i] = NfcA.class.getName();
                    break;
                case TagTechnology.NFC_B:
                    strings[i] = NfcB.class.getName();
                    break;
                case TagTechnology.NFC_F:
                    strings[i] = NfcF.class.getName();
                    break;
                case TagTechnology.NFC_V:
                    strings[i] = NfcV.class.getName();
                    break;
                case TagTechnology.NFC_BARCODE:
                    strings[i] = NfcBarcode.class.getName();
                    break;
                default:
                    throw new IllegalArgumentException("Unknown tech type " + techList[i]);
            }
        }
        return strings;
    }

    static int[] getTechCodesFromStrings(String[] techStringList) throws IllegalArgumentException {
        if (techStringList == null) {
            throw new IllegalArgumentException("List cannot be null");
        }
        int[] techIntList = new int[techStringList.length];
        HashMap<String, Integer> stringToCodeMap = getTechStringToCodeMap();
        for (int i = 0; i < techStringList.length; i++) {
            Integer code = stringToCodeMap.get(techStringList[i]);

            if (code == null) {
                throw new IllegalArgumentException("Unknown tech type " + techStringList[i]);
            }

            techIntList[i] = code.intValue();
        }
        return techIntList;
    }

    private static HashMap<String, Integer> getTechStringToCodeMap() {
        HashMap<String, Integer> techStringToCodeMap = new HashMap<String, Integer>();

        techStringToCodeMap.put(IsoDep.class.getName(), TagTechnology.ISO_DEP);
        techStringToCodeMap.put(MifareClassic.class.getName(), TagTechnology.MIFARE_CLASSIC);
        techStringToCodeMap.put(MifareUltralight.class.getName(), TagTechnology.MIFARE_ULTRALIGHT);
        techStringToCodeMap.put(Ndef.class.getName(), TagTechnology.NDEF);
        techStringToCodeMap.put(NdefFormatable.class.getName(), TagTechnology.NDEF_FORMATABLE);
        techStringToCodeMap.put(NfcA.class.getName(), TagTechnology.NFC_A);
        techStringToCodeMap.put(NfcB.class.getName(), TagTechnology.NFC_B);
        techStringToCodeMap.put(NfcF.class.getName(), TagTechnology.NFC_F);
        techStringToCodeMap.put(NfcV.class.getName(), TagTechnology.NFC_V);
        techStringToCodeMap.put(NfcBarcode.class.getName(), TagTechnology.NFC_BARCODE);

        return techStringToCodeMap;
    }

    For use by NfcService only.
@hide /**
     * For use by NfcService only.
     * @hide
     */
    public int getServiceHandle() {
        return mServiceHandle;
    }

    For use by NfcService only.
@hide /**
     * For use by NfcService only.
     * @hide
     */
    public int[] getTechCodeList() {
        return mTechList;
    }

    Get the Tag Identifier (if it has one).
The tag identifier is a low level serial number, used for anti-collision
and identification.
 Most tags have a stable unique identifier
(UID), but some tags will generate a random ID every time they are discovered
(RID), and there are some tags with no ID at all (the byte array will be zero-sized).
 The size and format of an ID is specific to the RF technology used by the tag.
 This function retrieves the ID as determined at discovery time, and does not
perform any further RF communication or block.
Returns: ID as byte array, never null/**
     * Get the Tag Identifier (if it has one).
     * <p>The tag identifier is a low level serial number, used for anti-collision
     * and identification.
     * <p> Most tags have a stable unique identifier
     * (UID), but some tags will generate a random ID every time they are discovered
     * (RID), and there are some tags with no ID at all (the byte array will be zero-sized).
     * <p> The size and format of an ID is specific to the RF technology used by the tag.
     * <p> This function retrieves the ID as determined at discovery time, and does not
     * perform any further RF communication or block.
     * @return ID as byte array, never null
     */
    public byte[] getId() {
        return mId;
    }

    Get the technologies available in this tag, as fully qualified class names.
 A technology is an implementation of the TagTechnology interface, and can be instantiated by calling the static get(Tag) method on the implementation with this Tag. The TagTechnology object can then be used to perform advanced, technology-specific operations on a tag. 
 Android defines a mandatory set of technologies that must be correctly enumerated by all Android NFC devices, and an optional set of proprietary technologies. See TagTechnology for more details. 

The ordering of the returned array is undefined and should not be relied upon.
Returns: an array of fully-qualified TagTechnology class-names./**
     * Get the technologies available in this tag, as fully qualified class names.
     * <p>
     * A technology is an implementation of the {@link TagTechnology} interface,
     * and can be instantiated by calling the static <code>get(Tag)</code>
     * method on the implementation with this Tag. The {@link TagTechnology}
     * object can then be used to perform advanced, technology-specific operations on a tag.
     * <p>
     * Android defines a mandatory set of technologies that must be correctly
     * enumerated by all Android NFC devices, and an optional
     * set of proprietary technologies.
     * See {@link TagTechnology} for more details.
     * <p>
     * The ordering of the returned array is undefined and should not be relied upon.
     * @return an array of fully-qualified {@link TagTechnology} class-names.
     */
    public String[] getTechList() {
        return mTechStringList;
    }

    Rediscover the technologies available on this tag.
 The technologies that are available on a tag may change due to operations being performed on a tag. For example, formatting a tag as NDEF adds the Ndef technology. The rediscover method reenumerates the available technologies on the tag and returns a new Tag object containing these technologies. 
 You may not be connected to any of this Tag's technologies when calling this method. This method guarantees that you will be returned the same Tag if it is still in the field. 
May cause RF activity and may block. Must not be called from the main application thread. A blocked call will be canceled with IOException by calling close from another thread. 
Does not remove power from the RF field, so a tag having a random
ID should not change its ID.
Throws: IOException – if the tag cannot be rediscovered
Returns: the rediscovered tag object.
@hide /**
     * Rediscover the technologies available on this tag.
     * <p>
     * The technologies that are available on a tag may change due to
     * operations being performed on a tag. For example, formatting a
     * tag as NDEF adds the {@link Ndef} technology. The {@link rediscover}
     * method reenumerates the available technologies on the tag
     * and returns a new {@link Tag} object containing these technologies.
     * <p>
     * You may not be connected to any of this {@link Tag}'s technologies
     * when calling this method.
     * This method guarantees that you will be returned the same Tag
     * if it is still in the field.
     * <p>May cause RF activity and may block. Must not be called
     * from the main application thread. A blocked call will be canceled with
     * {@link IOException} by calling {@link #close} from another thread.
     * <p>Does not remove power from the RF field, so a tag having a random
     * ID should not change its ID.
     * @return the rediscovered tag object.
     * @throws IOException if the tag cannot be rediscovered
     * @hide
     */
    // TODO See if we need TagLostException
    // TODO Unhide for ICS
    // TODO Update documentation to make sure it matches with the final
    //      implementation.
    public Tag rediscover() throws IOException {
        if (getConnectedTechnology() != -1) {
            throw new IllegalStateException("Close connection to the technology first!");
        }

        if (mTagService == null) {
            throw new IOException("Mock tags don't support this operation.");
        }
        try {
            Tag newTag = mTagService.rediscover(getServiceHandle());
            if (newTag != null) {
                return newTag;
            } else {
                throw new IOException("Failed to rediscover tag");
            }
        } catch (RemoteException e) {
            throw new IOException("NFC service dead");
        }
    }


    @hide /** @hide */
    public boolean hasTech(int techType) {
        for (int tech : mTechList) {
            if (tech == techType) return true;
        }
        return false;
    }

    @hide /** @hide */
    public Bundle getTechExtras(int tech) {
        int pos = -1;
        for (int idx = 0; idx < mTechList.length; idx++) {
          if (mTechList[idx] == tech) {
              pos = idx;
              break;
          }
        }
        if (pos < 0) {
            return null;
        }

        return mTechExtras[pos];
    }

    @hide /** @hide */
    public INfcTag getTagService() {
        return mTagService;
    }

    Human-readable description of the tag, for debugging.
/**
     * Human-readable description of the tag, for debugging.
     */
    @Override
    public String toString() {
        StringBuilder sb = new StringBuilder("TAG: Tech [");
        String[] techList = getTechList();
        int length = techList.length;
        for (int i = 0; i < length; i++) {
            sb.append(techList[i]);
            if (i < length - 1) {
                sb.append(", ");
            }
        }
        sb.append("]");
        return sb.toString();
    }

    /*package*/ static byte[] readBytesWithNull(Parcel in) {
        int len = in.readInt();
        byte[] result = null;
        if (len >= 0) {
            result = new byte[len];
            in.readByteArray(result);
        }
        return result;
    }

    /*package*/ static void writeBytesWithNull(Parcel out, byte[] b) {
        if (b == null) {
            out.writeInt(-1);
            return;
        }
        out.writeInt(b.length);
        out.writeByteArray(b);
    }

    @Override
    public int describeContents() {
        return 0;
    }

    @Override
    public void writeToParcel(Parcel dest, int flags) {
        // Null mTagService means this is a mock tag
        int isMock = (mTagService == null)?1:0;

        writeBytesWithNull(dest, mId);
        dest.writeInt(mTechList.length);
        dest.writeIntArray(mTechList);
        dest.writeTypedArray(mTechExtras, 0);
        dest.writeInt(mServiceHandle);
        dest.writeInt(isMock);
        if (isMock == 0) {
            dest.writeStrongBinder(mTagService.asBinder());
        }
    }

    public static final Parcelable.Creator<Tag> CREATOR =
            new Parcelable.Creator<Tag>() {
        @Override
        public Tag createFromParcel(Parcel in) {
            INfcTag tagService;

            // Tag fields
            byte[] id = Tag.readBytesWithNull(in);
            int[] techList = new int[in.readInt()];
            in.readIntArray(techList);
            Bundle[] techExtras = in.createTypedArray(Bundle.CREATOR);
            int serviceHandle = in.readInt();
            int isMock = in.readInt();
            if (isMock == 0) {
                tagService = INfcTag.Stub.asInterface(in.readStrongBinder());
            }
            else {
                tagService = null;
            }

            return new Tag(id, techList, techExtras, serviceHandle, tagService);
        }

        @Override
        public Tag[] newArray(int size) {
            return new Tag[size];
        }
    };

    For internal use only.
@hide /**
     * For internal use only.
     *
     * @hide
     */
    public synchronized void setConnectedTechnology(int technology) {
        if (mConnectedTechnology == -1) {
            mConnectedTechnology = technology;
        } else {
            throw new IllegalStateException("Close other technology first!");
        }
    }

    For internal use only.
@hide /**
     * For internal use only.
     *
     * @hide
     */
    public int getConnectedTechnology() {
        return mConnectedTechnology;
    }

    For internal use only.
@hide /**
     * For internal use only.
     *
     * @hide
     */
    public void setTechnologyDisconnected() {
        mConnectedTechnology = -1;
    }
}
Params:	id – The tag identifier, can be null techList – must not be null
Returns:	freshly constructed tag
@hide
Throws:	IOException – if the tag cannot be rediscovered
Returns:	the rediscovered tag object.
@hide
/

android/ android-9.0.0_r35/ android/nfc/Tag.java

Tag Dispatch

1. Foreground activity dispatch

2. NDEF data dispatch

3. Tag Technology dispatch

4. Fall-back dispatch

NFC Tag Background
