Android NFC, do a null check in onCreate?

Question

I have code to initialize my NFC adapter, but I am not sure how to intialize the variables during the onCreate. The app can be initialized whether an NFC TAG is in proximity or not, ie. if someone simply opened the app. So when I get down to this line NfcV nfcMessage = NfcV.get(new TagGet().getTag()); it crashes because it is null, there is no tag there if you just load the app on your own. How do I check here for != null I'm not sure which part to check or how to structure this code.

The result is that I want to read the contents of the tag IFF a tag is present. Otherwise just load the layout and wait for a NfcV tag to be scanned.

// Setup an intent filter for all MIME based dispatches
    IntentFilter nfcv = new IntentFilter(NfcAdapter.ACTION_TAG_DISCOVERED);
    try {
        nfcv.addDataType("*/*");
    } catch (MalformedMimeTypeException e) {
        throw new RuntimeException("fail", e);
    }
    mFilters = new IntentFilter[] {
            nfcv,
    };

    // Setup a tech list for all NfcF tags
    mTechLists = new String[][] { new String[] { NfcV.class.getName() } };

    //mAdapter.enableForegroundDispatch(this, mPendingIntent, mFilters, mTechLists);

    NfcV nfcMessage = NfcV.get(new TagGet().getTag());

    byte[] data = new byte[2048]; //tag length can't be any larger
    String value = "";
    try {
        data = nfcMessage.transceive(new byte[2048]);
        value = new String(data);
    } catch (IOException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();

Answer 1

Hear is a code outline of the basic way I made my first Nfc app. I tried to replace values (I used nfcA instead of nfcV) so you could read it better. It is a very basic structure, and you would need to fill in parts with your own code, but It should give you a good idea of how the structure of an NFC app can work.

public class Android_nfc_ibox extends Activity implements Runnable {




NfcAdapter mNfcAdapter;
private String[][] mTechLists;
PendingIntent pendingIntent;
Tag tag;
NfcA mTag;

/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    // Initialize the NFC adapter
    mNfcAdapter = NfcAdapter.getDefaultAdapter(this);
    if (mNfcAdapter != null) {
        dialog_text.append("Tap an NFC tag for access\n\r");
    } else {
        dialog_text.append("This phone is not NFC enabled\n\r");
    }

    // Create the PendingIntent object which will contain the details of the tag that has been scanned
    pendingIntent = PendingIntent.getActivity(this, 0, new Intent(this, getClass()).addFlags(Intent.FLAG_ACTIVITY_SINGLE_TOP), 0);

    // Setup a tech list for all desired tag types
    mTechLists = new String[][] { new String[] { NfcA.class.getName() } };

}

    /** Re-enable the tag dispatch if the app is in the foreground */
   @Override
    public void onResume() {
        super.onResume();
        if (mNfcAdapter != null) mNfcAdapter.enableForegroundDispatch(this, pendingIntent, null, mTechLists);
    }

   /** Disable the tag dispatch when the app is no longer in the foreground */
    @Override
    public void onPause() {
        super.onPause();
        if (mNfcAdapter != null) mNfcAdapter.disableForegroundDispatch(this);
    }

    /** A tag has been discovered */
    @Override 
    public void onNewIntent(Intent intent){

        // get the tag object for the discovered tag
        Tag tag = intent.getParcelableExtra(NfcAdapter.EXTRA_TAG);

        // try and get the MifareUltralight instance for this tag
        mTag = NfcV.get(tag);

        // if null then this wasn't a NfcV tag so wait for next time
        if(mTag == null){
            dialog_text.append("Not a Nfc V tag\n\r");
        }

           // Start the tag communications thread
           Thread myThread = new Thread(this);
           myThread.start();

        }
    }

   // (we could create other threads for other types of tags)
   public void run(){
       // try to connect to the Nfc V tag
       try{

           mTag.connect();
       }catch(IOException e){
            //handle the error here
       }

       //this will send raw data
       //send the values you want in the byte[]
       //just add the raw hex values with commas
       //pageBuffer is an array that will hold the response
       try{
           pageBuffer = mTag.transceive(new byte[] {0x11, 0x24, 0x11});
       }catch(IOException e){
            //handle error here
       }
    } 

}