How to find out whether an NFC tag is still in range of an Android now?

Question

As I know when an Android phone gets an NFC tag touched, it will send an event (NDEF_DISCOVERED intent), but Android doesn\'t seem to care whether this tag is staying in pla

Answer 1

As part of the NFC intent received by your activity, you will also receive a tag-handle (Tag object) in an intent extra:

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

Depending on the type of tag, you can then get an instance of the specific tag technology. For instance, if it's an NDEF tag, you can get:

Ndef ndefTag = Ndef.get(tag);

Then you can connect to the tag using the connect() method:

ndefTag.connect();

After that you can check if the tag is still "connected" to the device by periodically trying to read from the tag:

try {
    ndefTag.getNdefMessage();
} catch (IOException e) {
    // if you receive an IOException, contact to the tag has been lost
}

Note that this will only work if your activity is in the foreground all the time and the screen remains on.