I got an application that reads and writes nfc tags with ndef data format. This all seems to be ok. But whenever i try to get closer a tag to my phone, it produces a new activity. I only want to obtain data on the tag without opening new intent. So i can make my app decide whether the tag has been tapped two times in a row.
The code that i handle coming tags:
public class MainActivity extends Activity {
public static Context myContext;
private Button myButton;
private int currentID, currentBalance;
protected void onCreate(Bundle savedInstanceState) { // Firstly Created when
// a tag tapped to
// the phone
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
myButton = (Button) findViewById(R.id.button1);
currentID = 0;
currentBalance = 0;
myButton.setOnClickListener(new View.OnClickListener() { // Tag write
// function
// places
// here
public void onClick(View arg0) {
Intent i = new Intent(getApplicationContext(), nfcWrite.class);
i.putExtra("id",currentID);
i.putExtra("balance",currentBalance);
startActivity(i);
}
});
}
#Override
protected void onResume() {
// TODO Auto-generated method stub
super.onResume();
Intent intent = getIntent();
if (NfcAdapter.ACTION_NDEF_DISCOVERED.equals(getIntent().getAction())) {
Parcelable[] rawMsgs = intent.getParcelableArrayExtra(NfcAdapter.EXTRA_NDEF_MESSAGES);
NdefRecord myRecord = ((NdefMessage) rawMsgs[0]).getRecords()[0];
String nfcData = new String(myRecord.getPayload());
String[] splitData = nfcData.split("-");
currentID = Integer.parseInt(splitData[0]);
currentBalance = Integer.parseInt(splitData[1]);
Toast.makeText(getApplicationContext(), nfcData, Toast.LENGTH_LONG).show();
}
}
}
Add android:launchMode="singleTask" to the <activity> element for MainActivity. Note that if the activity is already running, onNewIntent() will be called, instead of onCreate(), to deliver the NDEF Intent to you. Hence, you will need to handle the NDEF Intent in both onCreate() (if the activity was not already running) and onNewIntent() (if the activity was already running).
This sample project illustrates the technique.
Instead of setting the launch-mode of the activity that receives the NFC intents to "singleTask" (see CommonsWare's answer), the preferred way for NFC applications to receive NFC-related intents while the app is in foreground is the foreground dispatch system (or alternatively the reader mode API when using only Android 4.4).
In order to use the foreground dispatch, you would create a pending intent like this:
PendingIntent pendingIntent = PendingIntent.getActivity(
this,
0,
new Intent(this, getClass()).addFlags(Intent.FLAG_ACTIVITY_SINGLE_TOP),
0);
Then, in your activity's onResume() method, you would enable the foreground dispatch like this:
NfcAdapter nfcAdapter = NfcAdapter.getDefaultAdapter(this);
nfcAdapter.enableForegroundDispatch(this, pendingIntent, null, null);
You will then receive intents notifying you about discovered tags through the activity's onNewIntent() method:
public void onNewIntent(Intent intent) {
...
}
Moreover, you have to disable the foreground dispatch in your activity's onPause() method:
NfcAdapter nfcAdapter = NfcAdapter.getDefaultAdapter(this);
nfcAdapter.disableForegroundDispatch(this);
Related
I am building an Android app using Eclipse and Android SDK. I would like to implement an NFC P2P function in my app in the sense that when you place the 2 phones back to back, both send a string and receive a string automatically. This would of course happen in a separate activity. I have managed to send a custom tag (String) but have been unable to intercept it and use it afterwards in the app code. How can I do this?
This is what I have so far:
public class MainActivity extends Activity {
public NfcAdapter mAdapter;
PendingIntent mPendingIntent;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
mAdapter = NfcAdapter.getDefaultAdapter(this);
NdefRecord rec = NdefRecord.createUri("www.stackoverflow.com");
NdefMessage ndef = new NdefMessage(rec);
mAdapter.setNdefPushMessage(ndef, this);
}
I have spent a lot of time trying to find and understand solutions to intercept the tag. Unsuccessfully.
Thank you for your help.
You can use the foreground dispatch system to receive the NDEF message within your activity:
In onResume():
PendingIntent pendingIntent = PendingIntent.getActivity(this, 0, new Intent(this, getClass()).addFlags(Intent.FLAG_ACTIVITY_SINGLE_TOP), 0);
NfcAdapter nfcAdapter = NfcAdapter.getDefaultAdapter(this);
nfcAdapter.enableForegroundDispatch(this, pendingIntent, null, null);
Do something upon receiving the intent:
public void onNewIntent(Intent intent) {
...
}
I have created an application which gets the NFC UID and changes a text view to the ID however, when i try to do more things with the application, i get an error message. For example, if i try to say... if the UID = "001hghg" then change another text view to "success!" Therefore i was wondering if its possible to start the application first, scan the tag and within the onCreate or onResume method, change the text view. Here is the code below:
public class MainActivity extends Activity {
TextView tvUID;
// list of NFC technologies detected:
private final String[][] techList = new String[][] {
new String[] {
NfcA.class.getName(),
NfcB.class.getName(),
NfcF.class.getName(),
NfcV.class.getName(),
NdefFormatable.class.getName(),
TagTechnology.class.getName(),
IsoDep.class.getName(),
MifareClassic.class.getName(),
MifareUltralight.class.getName(),
Ndef.class.getName()
}
};
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
}
#Override
protected void onStart() {
// TODO Auto-generated method stub
super.onStart();
}
#Override
protected void onResume() {
super.onResume();
// creating pending intent:
PendingIntent pendingIntent = PendingIntent.getActivity(this, 0, new Intent(this, getClass()).addFlags(Intent.FLAG_ACTIVITY_SINGLE_TOP), 0);
// creating intent receiver for NFC events:
IntentFilter filter = new IntentFilter();
filter.addAction(NfcAdapter.ACTION_TAG_DISCOVERED);
filter.addAction(NfcAdapter.ACTION_NDEF_DISCOVERED);
filter.addAction(NfcAdapter.ACTION_TECH_DISCOVERED);
// enabling foreground dispatch for getting intent from NFC event:
NfcAdapter nfcAdapter = NfcAdapter.getDefaultAdapter(this);
nfcAdapter.enableForegroundDispatch(this, pendingIntent, new IntentFilter[]{filter}, this.techList);
}
#Override
protected void onNewIntent(Intent intent) {
if (intent.getAction().equals(NfcAdapter.ACTION_TAG_DISCOVERED)) {
tvUID = (TextView) findViewById(R.id.tvUID);
tvUID.setText(ByteArrayToHexString(intent.getByteArrayExtra(NfcAdapter.EXTRA_ID)));
}
}
private 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;
}
}
Intents are Android's means of inter-process communication. Consequently, being notified about actions external to your applications typically involves notifications through intents. A user scanning an NFC tag is an action that happens outside of your application, so you want your application to be somehow notified about that event. In general, the NFC service does this by sending an intent, and your application registers to receive that intent.
On Android < 4.4, intents were the only way of receiving a notification on NFC tag events. While your app is running, you can either receive them through onNewIntent (intent filters in manifest, foreground dispatch) or through onActivityResult (foreground dispatch).
Starting with Android 4.4, there is a new reader-mode API. THis API permits you to register for a specific callback onTagDiscovered to be triggered upon tag detection.
So yes, you can be notified about tag discovery through other callback methods than onNewIntent. But no, the onCreate method will be the first method invoked when your activity is created. onStart and onResume immediately follow that method. So there is no way to scan that tag in between starting your activity manually and invokation of these methods.
However, if you activity has been started by an NFC intent, you can get that intent with the activity's getIntent method. This also works in any of the methods onCreate, onStart and onResume.
The action you are checking (ACTION_TAG_DISCOVERED) is bypassed by ACTION_NDEF_DISCOVERED. I worked on a NFC project recently and for some reason every time I would use this action it wouldn't pass (even with the action_tag_discovered filter). So I started checking discovery with TECH and NDEF_DISCOVERED only.
I don't know if this is of any help, but it kinda solved all my problems 8-)
Maybe you could post the error you are getting?
And which environment you are using. Are you using Android Studio and a phone linked with adb?
I'm guessing most of you face palmed when you saw this title, and thought we've seen this before well I agree, but I've tried everything to solve this issue and it wont remedy. So here goes.
My app can be launched from the home screen(icon) and everything works OK it scans a NFC tag and sends the relevant data to the server.
However what I also want is for the App to be launched from NFC tag, which it does no problem.
However! when the app is launched via the NFC tag you then remove the phone and re-present it to the tag it should then read the tag and send the data to the server. Exactly the same behaviour as launching the app via the the icon, but when you scan the NFC tag this time a new instance of the app is launched which ultimately kicks the current instance down the stack, the version of the instance that was busy reading the tag so I get a ANR.
in a nutshell:
from home screen -> scan a tag -> app launches.
you then rescan the tag->
The current instance of the app disappears to be replaced by a new instance.
I want the previous instance to stay where it was and work.
A few guesses from me at this point would be that:
-The NFC is not getting properly registered to app, hence the the OS doing default behaviour.
-There is a flag not being set correctly when launched via a NFC tag telling the OS the activity does not need to relaunched.
anyway here's the code:
<uses-permission android:name="android.permission.NFC"/>
<intent-filter>
<action android:name="android.nfc.action.NDEF_DISCOVERED" />
<category android:name="android.intent.category.DEFAULT" />
<data android:scheme="http"android:host="#string/URL_for_intent_filtering" android:pathPrefix="/id/" />
//Procedure of NFC startup called from OnCreate
private void startNFC()
{
mNfcAdapter = NfcAdapter.getDefaultAdapter(this);
if(! mNfcAdapter.isEnabled())//check the NFC is switched on
{
mMainActivityHandler.sendEmptyMessage(NFC_DISABLED);
}
//its ok to carry on and instantiate the NFC even though its not enabled.
if(mNfcAdapter != null)
{
int requestID = (int) System.currentTimeMillis();
mPendingIntent = PendingIntent.getActivity(this, requestID, new Intent(this, getClass()).addFlags(Intent.FLAG_ACTIVITY_SINGLE_TOP), PendingIntent.FLAG_UPDATE_CURRENT);
IntentFilter intentF = new IntentFilter(NfcAdapter.ACTION_NDEF_DISCOVERED);
intentF.addDataScheme("http");
intentfilter = new IntentFilter[] {intentF};
if(DEBUG) Log.i("DEBUG","+++++++++++++++++++++++++++++++++++++++++++++++ NFC HAS BEEN STARTED");
}else
{
//we have a problem with the NFC adapter probably because the device doesn't have one.
if(DEBUG) Log.i("DEBUG","+++++++++++++++++++++++++++++++++++++++++++++++ NFC HAS FAILED");
mMainActivityHandler.sendEmptyMessage(NFC_FAILED);
}
}
#Override
protected void onPause()
{
if(DEBUG) Log.i("MA","+++++++++++++++++++++++++++++++++++++++ ON PAUSE");
try{
mNfcAdapter.disableForegroundDispatch(this);
}catch(Exception e)
{
}
super.onPause();
}
//and here we should reinstate the NFC adapter
#Override
protected void onResume()
{
if(DEBUG) Log.i("MA","+++++++++++++++++++++++++++++++++++++++ ON RESUME");
//setupDataListener(true);
setupServerComms(getApplicationContext());
//mNfcAdapter.enableForegroundDispatch(this,mPendingIntent,intentfilter,null);
mNfcAdapter.enableForegroundDispatch(this,mPendingIntent,null,null);
super.onResume();
}
Just add this line in your AndroidManifest.xml into your Activity and you are probably done.
android:launchMode="singleTask"
So what you want is for the app to catch the intent and then read the information and do something with it correct? Well you have a pending intent that is used to do this but your setup seems a little different from what I usually do. Here is an example of how I use a pending intent to catch the tag data (from there you can do whatever you want like send it to a server):
Class example{
NfcAdapter adapter;
Tag motor;
String FileName;
PendingIntent detectTag;
IntentFilter NFC;
IntentFilter [] Catcher;
String [][] TechList;
TextView readToField;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_my_activity);
// Catch NFC detects
adapter = NfcAdapter.getDefaultAdapter(this);
detectTag = PendingIntent.getActivity(this,0,new Intent(this, getClass()).addFlags(Intent.FLAG_ACTIVITY_SINGLE_TOP), 0);
NFC = new IntentFilter(NfcAdapter.ACTION_TAG_DISCOVERED);
Catcher = new IntentFilter[] {NFC,};
TechList = new String [][]{new String[]{android.nfc.tech.NfcV.class.getName()}};
}
public void onNewIntent(Intent intent)
{
super.onNewIntent(intent);
motor = intent.getParcelableExtra(NfcAdapter.EXTRA_TAG);
Bridge bridge = (Bridge) getApplication();
bridge.setCurrentTag(motor);
}
public void onPause()
{
super.onPause();
adapter.disableForegroundDispatch(this);
}
public void onResume()
{
super.onResume();
adapter.enableForegroundDispatch(this,detectTag ,Catcher , TechList);
}
}
The Bridge object is just a class I use to save the tag information so I can send information to tags from other (behind the scenes) classes.
Finally, I have always been told that for onResume and onPause you should call the super.method first.
I am developing an app that will use NFC tags for identification. All examples I find however, are about starting an app when a certain card is read. I tried looking for an example or documentation on how to do it differently, to no avail.
What I want is:
user starts my app
user scans NFC card
app decides next step
I got some code working now, I just don't get the tag data:
In onCreate:
pendingIntent = PendingIntent.getActivity(this, 0, new Intent(this,
getClass()).addFlags(Intent.FLAG_ACTIVITY_SINGLE_TOP), 0);
tech = new IntentFilter(NfcAdapter.ACTION_TECH_DISCOVERED);
try {
tech.addDataType("*/*");
} catch (MalformedMimeTypeException e) {
throw new RuntimeException("fail", e);
}
intentFiltersArray = new IntentFilter[] { tech };
And in onResume:
nfcAdapter.enableForegroundDispatch(this, pendingIntent, intentFiltersArray, techList);
The intent only gets there when the app is active, but the Intent I receive is the PendingIntent I defined myself, not the ACTION_TECH_DISCOVERED intent I want.
I found part of the answer here: NFC broadcastreceiver problem
That solution doesn't provide a complete working example, so I tried a little extra. To help future visitors, I'll post my solution. It is a NfcActivity which subclasses Activity, if you subclass this NfcActivity, all you have to do is implement its NfcRead method, and you're good to go:
public abstract class NfcActivity extends Activity {
// NFC handling stuff
PendingIntent pendingIntent;
NfcAdapter nfcAdapter;
#Override
public void onResume() {
super.onResume();
pendingIntent = PendingIntent.getActivity(this, 0, new Intent(this,
getClass()).addFlags(Intent.FLAG_ACTIVITY_SINGLE_TOP), 0);
nfcAdapter = NfcAdapter.getDefaultAdapter(this);
nfcAdapter.enableForegroundDispatch(this, pendingIntent, null, null);
}
#Override
protected void onPause() {
super.onPause();
nfcAdapter.disableForegroundDispatch(this);
}
// does nothing, has to be overridden in child classes
public abstract void NfcRead(Intent intent);
#Override
public void onNewIntent(Intent intent) {
String action = intent.getAction();
if (NfcAdapter.ACTION_TAG_DISCOVERED.equals(action)) {
NfcRead(intent);
}
}
}
If you want that the user first starts your app and only then scans an NFC card, I would recommend using NFC foreground dispatch. In that way, your Activity does not need to have any intent filters in the manifest (and thus will never be called by accident when the user scans another NFC card).
With foreground dispatch enabled, your Activity can receive all NFC intents directly (without any app chooser pop-ups) and decide what to do with it (e.g. pass it on to another Activity).
I've made an app that is called when the intent android.nfc.action.TAG_DISCOVERED is sent, but then I want to get the info of the card in the onNewIntent method, but I don't know how to handle this kind of nfc cards. I tried with the following code:
public void onNewIntent(Intent intent) {
Tag tagFromIntent = intent.getParcelableExtra(NfcAdapter.EXTRA_TAG);
//do something with tagFromIntent
NfcA nfca = NfcA.get(tagFromIntent);
try{
nfca.connect();
Short s = nfca.getSak();
byte[] a = nfca.getAtqa();
String atqa = new String(a, Charset.forName("US-ASCII"));
tv.setText("SAK = "+s+"\nATQA = "+atqa);
nfca.close();
}
catch(Exception e){
Log.e(TAG, "Error when reading tag");
tv.setText("Error");
}
}
tv is a TextView, but when this code is executed it never gets changed.
OnNewIntent is called if your activity is already running and is set to be singleTask.
You'll want to make the code it's own method and call it in onCreate() as well as onNewIntent()
If you have other apps that can manage the same tag at higher level (NDEF_DISCOVERED or TECH_DISCOVERED) your app, that manage only the lower level, never will be called.
To use your app you need to open your app, than scan the tag.
If your app never starts, be sure to have done these steps:
In OnCreate() get your NfcAdapter:
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
....
mNfcAdapter = NfcAdapter.getDefaultAdapter(this);
if (mNfcAdapter == null) {
// Stop here, we definitely need NFC
Toast.makeText(this, "This device doesn't support NFC.", Toast.LENGTH_LONG).show();
finish();
return;
}
//method to handle your intent
handleTag(getIntent());
}
In onResume enable the foreground dispatch:
#Override
public void onResume() {
super.onResume();
final Intent intent = new Intent(this.getApplicationContext(), this.getClass());
final PendingIntent pendingIntent = PendingIntent.getActivity(this.getApplicationContext(), 0, intent, 0);
mNfcAdapter.enableForegroundDispatch(this, pendingIntent, null, null);
}
In onPause disable it:
#Override
protected void onPause() {
mNfcAdapter.disableForegroundDispatch(this);
super.onPause();
}
In onNewIntent call the function to handle your intent
#Override
protected void onNewIntent(Intent intent) {
super.onNewIntent(intent);
handleTag(intent);
}
In your function handle your tag:
private void handleTag(Intent intent){
String action = intent.getAction();
Tag tag = intent.getParcelableExtra(NfcAdapter.EXTRA_TAG);
if (NfcAdapter.ACTION_TAG_DISCOVERED.equals(action){
// here your code
}
}
Don't forget to add the permissions in your manifest:
<uses-permission android:name="android.permission.NFC" />
<uses-feature
android:name="android.hardware.nfc"
android:required="true" />
<activity>
....
<intent-filter>
<action android:name="android.nfc.action.TAG_DISCOVERED"/>
</intent-filter>
</activity>
More info here NFC Basis and here Read NFC tags