How to detect NFC tag was removed

问题

I am new at NFC technology. I am trying to read and write Mifare Classic 4K tags. I succeeded reading and writing. I can detect the tag on onNewIntent action.

My problem is that I could't detect when an NFC tag was removed (similar to onNewIntent when detecting a tag).

How can I solve this problem?

回答1:

There is no event that notifies your app if a tag is removed from the reader. A typical approach to detect removal is to actively poll the tag (e.g. by reading an NDEF message or a data block) until you receive IOException indicating that communication with the tag was lost.

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UPDATE

As of Android API level 24 this is no longer true. There is now a method

NfcAdapter.ignore(tag, debounceMs, tagRemovedListener, handler);

that can be used to register a callback for getting notifications upon tag removal. This method may have some issue though, so carefully read the documentation on side-effects/corner cases.

来源：https://stackoverflow.com/questions/36126635/how-to-detect-nfc-tag-was-removed