アプリのユーザーから取得した情報をアプリが書き込めるかどうかわからない。タグへの書き込みボタンを押すと、アプリがクラッシュし続けます。私は通常EditText、ユーザー入力用に5つあります。次に、これらの値を使用して、NFCタグに書き込む文字列を作成します。（この情報は、別のアプリを使用して読み取られ、文字列が再び別のコンポーネントに分割されます）。`
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
mNfcAdapter = NfcAdapter.getDefaultAdapter(this);
setContentView(R.layout.write_tag1);
findViewById(R.id.nfc_write_confirm).setOnClickListener(mTagWriter);
cancel3Button = (Button)findViewById(R.id.nfc_write_cancel);
foodName = (EditText)findViewById(R.id.nfc_food_name);
protValue = (EditText)findViewById(R.id.nfc_protein_value);
carbValue = (EditText)findViewById(R.id.nfc_carb_value);
fatValue = (EditText)findViewById(R.id.nfc_fat_value);
energyValue = (EditText)findViewById(R.id.nfc_energy_value);
allValue = (TextView)findViewById(R.id.nfc_all_value);
IntentFilter tagDetected = new IntentFilter(NfcAdapter.ACTION_TAG_DISCOVERED);
mWriteTagFilters = new IntentFilter[] {
tagDetected
};
cancel3Button.setOnClickListener(new Button.OnClickListener(){
public void onClick(View v) {
finish();
}
});
}
@Override
protected void onNewIntent(Intent intent) {
if (mWriteMode && NfcAdapter.ACTION_TAG_DISCOVERED.equals(intent.getAction())) {
Tag detectedTag = intent.getParcelableExtra(NfcAdapter.EXTRA_TAG);
writeTag(getNoteAsNdef(), detectedTag);
}
}
private View.OnClickListener mTagWriter = new View.OnClickListener() {
public void onClick(View v) {
// Write to a tag for as long as the dialog is shown.
enableTagWriteMode();
new AlertDialog.Builder(NFCWriteTag1.this).setTitle("Touch tag to write")
.setOnCancelListener(new DialogInterface.OnCancelListener() {
public void onCancel(DialogInterface dialog) {
disableTagWriteMode();
}
}).create().show();
}
};
private NdefMessage getNoteAsNdef() {
String a, b, c, d, e;
a = (foodName.getText() + ",").toString();
b = (protValue.getText() + ",").toString();
c = (carbValue.getText() + ",").toString();
d = (fatValue.getText() + ",").toString();
e = energyValue.getText().toString();
allValue.setText(a+b+c+d+e);
byte[] textBytes = allValue.getText().toString().getBytes();
NdefRecord textRecord = new NdefRecord(NdefRecord.TNF_MIME_MEDIA, "text/plain".getBytes(),
new byte[] {}, textBytes);
return new NdefMessage(new NdefRecord[] {
textRecord
});
}
private void enableTagWriteMode() {
mWriteMode = true;
IntentFilter tagDetected = new IntentFilter(NfcAdapter.ACTION_TAG_DISCOVERED);
mWriteTagFilters = new IntentFilter[] {
tagDetected
};
mNfcAdapter.enableForegroundDispatch(this, null, mWriteTagFilters, null);
}
private void disableTagWriteMode() {
mWriteMode = false;
mNfcAdapter.disableForegroundDispatch(this);
}
boolean writeTag(NdefMessage message, Tag tag) {
int size = message.toByteArray().length;
try {
Ndef ndef = Ndef.get(tag);
if (ndef != null) {
ndef.connect();
if (!ndef.isWritable()) {
toast("Tag is read-only.");
return false;
}
if (ndef.getMaxSize() < size) {
toast("Tag capacity is " + ndef.getMaxSize() + " bytes, message is " + size
+ " bytes.");
return false;
}
ndef.writeNdefMessage(message);
toast("Wrote message to pre-formatted tag.");
return true;
} else {
NdefFormatable format = NdefFormatable.get(tag);
if (format != null) {
try {
format.connect();
format.format(message);
toast("Formatted tag and wrote message");
return true;
} catch (IOException e) {
toast("Failed to format tag.");
return false;
}
} else {
toast("Tag doesn't support NDEF.");
return false;
}
}
} catch (Exception e) {
toast("Failed to write tag");
}
return false;
}
private void toast(String text) {
Toast.makeText(this, text, Toast.LENGTH_SHORT).show();
}
}`
Logcat：
11-08 18:29:18.745: E/AndroidRuntime(23252): FATAL EXCEPTION: main
11-08 18:29:18.745: E/AndroidRuntime(23252): java.lang.NullPointerException
11-08 18:29:18.745: E/AndroidRuntime(23252): at android.nfc.NfcAdapter.enableForegroundDispatch(NfcAdapter.java:1079)
11-08 18:29:18.745: E/AndroidRuntime(23252): at com.nfc.tag.writing.mealplan.NFCWriteTag1.enableTagWriteMode(NFCWriteTag1.java:128)
11-08 18:29:18.745: E/AndroidRuntime(23252): at com.nfc.tag.writing.mealplan.NFCWriteTag1.access$0(NFCWriteTag1.java:122)
11-08 18:29:18.745: E/AndroidRuntime(23252): at com.nfc.tag.writing.mealplan.NFCWriteTag1$1.onClick(NFCWriteTag1.java:93)
11-08 18:29:18.745: E/AndroidRuntime(23252): at android.view.View.performClick(View.java:4211)
11-08 18:29:18.745: E/AndroidRuntime(23252): at android.view.View$PerformClick.run(View.java:17267)
11-08 18:29:18.745: E/AndroidRuntime(23252): at android.os.Handler.handleCallback(Handler.java:615)
11-08 18:29:18.745: E/AndroidRuntime(23252): at android.os.Handler.dispatchMessage(Handler.java:92)
11-08 18:29:18.745: E/AndroidRuntime(23252): at android.os.Looper.loop(Looper.java:137)
11-08 18:29:18.745: E/AndroidRuntime(23252): at android.app.ActivityThread.main(ActivityThread.java:4898)
11-08 18:29:18.745: E/AndroidRuntime(23252): at java.lang.reflect.Method.invokeNative(Native Method)
11-08 18:29:18.745: E/AndroidRuntime(23252): at java.lang.reflect.Method.invoke(Method.java:511)
11-08 18:29:18.745: E/AndroidRuntime(23252): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1006)
11-08 18:29:18.745: E/AndroidRuntime(23252): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:773)
11-08 18:29:18.745: E/AndroidRuntime(23252): at dalvik.system.NativeStart.main(Native Method)