在Android上将应用程序记录写入和读取到NFC标签

Question

I'm trying the following:

• Write a message to an NFC tag that contains a reference to my application as well as a short string with which I can identify the tag.
• Read that message.

To speed up testing a bit at the beginning I've used the app Tagwriter ( https://play.google.com/store/apps/details?id=com.nxp.nfc.tagwriter&hl=de ) to write a tag with my needs: "Create plain text" and "Add launch application" in the next window.

Upon contact with the tag my phone will start up my application, it'll even read the identifying string correctly. However I also want it to write the tag from my own application instead of referring to another one.

I've tested several approaches, none of them worked. Either my application isn't started at all or it can't read the string. Can anyone help me?

public static boolean writeTag(String textToWrite, Tag tag)
{
     Miscellaneous.logEvent("i", "NFC", "Attempting to write tag...", 2);

     String packageName = Miscellaneous.getAnyContext().getPackageName();       
     NdefRecord appRecord = NdefRecord.createApplicationRecord(packageName);
     // Record with actual data we care about
     NdefRecord textRecord = new NdefRecord(NdefRecord.TNF_MIME_MEDIA,
                                            new String("application/" + packageName)
                                            .getBytes(Charset.forName("US-ASCII")),
                                            null, textToWrite.getBytes());

     // Complete NDEF message with both records
     NdefMessage completeMessageToWrite = new NdefMessage(new NdefRecord[] {textRecord, appRecord});

     int size = completeMessageToWrite.toByteArray().length;
     try
     {
           Ndef ndef = Ndef.get(tag);
           if (ndef != null)
           {
                ndef.connect();
                if (ndef.isWritable() && ndef.getMaxSize() > size)
            {
                ndef.writeNdefMessage(completeMessageToWrite);
                Miscellaneous.logEvent("i", "NFC", "Done writing tag.", 2);
                return true;
            }
        }
        else
        {
            NdefFormatable format = NdefFormatable.get(tag);
            if (format != null)
            {
                try
                {
                    format.connect();
                    format.format(completeMessageToWrite);
                    Miscellaneous.logEvent("i", "NFC", "Done writing tag.", 2);
                    return true;
                }
                catch(IOException e)
                {
                    Miscellaneous.logEvent("e", "NFC", "Error writing tag: " + Log.getStackTraceString(e), 2);
                }
            }
        }
    }
    catch(Exception e)
    {
        Miscellaneous.logEvent("e", "NFC", "Error writing tag: " + Log.getStackTraceString(e), 2);
    }

    return false;
}

Answer 1

I'm sorry, could have been a bit more detailed. It appears I kind of solved my problem myself. I've been taking a bit of example code from this website and a bit from that website and... That's why I had to first do some cleaning up before answering here. In that process I kind of found the mistake. The write-function now looks like this:

public static boolean writeTag(String textToWrite, Tag tag)
{
    Miscellaneous.logEvent("i", "NFC", "Attempting to write tag...", 2);

    String packageName = Miscellaneous.getAnyContext().getPackageName();        
    NdefRecord appRecord = NdefRecord.createApplicationRecord(packageName);
    // Record with actual data we care about
    byte[] textBytes = textToWrite.getBytes();
    byte[] textPayload = new byte[textBytes.length + 3];
    textPayload[0] = 0x02; // 0x02 = UTF8
    textPayload[1] = 'e'; // Language = en
    textPayload[2] = 'n';
    System.arraycopy(textBytes, 0, textPayload, 3, textBytes.length);
    NdefRecord textRecord = new NdefRecord(NdefRecord.TNF_WELL_KNOWN, NdefRecord.RTD_TEXT, new byte[0], textPayload);

    // Complete NDEF message with both records
    NdefMessage completeMessageToWrite = new NdefMessage(new NdefRecord[] {textRecord, appRecord});
[...]
}

It appears the "apprecord" was fine, but the text record was not.