在我的新Java类（Tap.java）中实现以下空检查：
Bundle extras = getIntent().getExtras();
if (extras == null) {
Log.e(TAG, "received no extras!");
结果：
ViewCountry(11637): received no extras!
因此我相信我需要将附加内容捆绑到我创建的新类（Tap.java）以及它当前从我的CountryList.java捆绑到（ViewCountry.java）的类中。
如何实现这一目标？
我想扩展以下包以包含相同的数据（ROW_ID，arg3）：
Intent viewCon = new Intent(CountryList.this, ViewCountry.class);
viewCon.putExtra(ROW_ID, arg3);
startActivity(viewCon);
如何将其扩展为将数据发送到Tap.java？
public class Tap extends Enable {
private static final String TAG = ViewCountry.class.getName();
protected Message message;
NfcAdapter mNfcAdapter;
private static final int MESSAGE_SENT = 1;
private long rowID;
private TextView nameTv;
private TextView capTv;
private TextView codeTv;
private TextView timeTv;
private TextView ssidTv;
private TextView combined;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.view_country);
setDetecting(true);
startPushing();
setUpViews();
Bundle extras = getIntent().getExtras();
rowID = extras.getLong(CountryList.ROW_ID);
}
private void setUpViews() {
nameTv = (TextView) findViewById(R.id.nameText);
capTv = (TextView) findViewById(R.id.capText);
timeTv = (TextView) findViewById(R.id.timeEdit);
codeTv = (TextView) findViewById(R.id.codeText);
ssidTv = (TextView) findViewById(R.id.wifiSSID);
}
@Override
public NdefMessage createNdefMessage(NfcEvent event) {
Log.d(TAG, "Create message to be beamed");
String a = "";
String b = "";
String message1 = a + ssidTv.getText().toString() + ","
+ capTv.getText().toString() + b;
// create message to be pushed, for example
Message message = new Message();
// add text record
message.add(new TextRecord(message1));
// add 'my' external type record
// message.add(new GenericExternalTypeRecord("com.wifi.demo", "atype",
// "My data".getBytes(Charset.forName("UTF-8"))));
// encode to NdefMessage, will be pushed via beam (now!) (unless there
// is a collision)
return message.getNdefMessage();
}
/**
*
* Implementation of {@link OnNdefPushCompleteCallback} interface.
*
* This method is called after a successful transfer (push) of a message
* from this device to another.
*/
@Override
protected void onNdefPushCompleteMessage() {
// make toast
toast(R.string.nfcBeamed);
// vibrate
Vibrator vibe = (Vibrator) getSystemService(Context.VIBRATOR_SERVICE);
vibe.vibrate(500);
}
public void toast(int id) {
toast(getString(id));
}
public void toast(String message) {
Toast toast = Toast.makeText(this, message, Toast.LENGTH_LONG);
toast.setGravity(Gravity.CENTER_HORIZONTAL | Gravity.CENTER_VERTICAL,
0, 0);
toast.show();
}
/**
*
* NFC was found and enabled in settings, and push is enabled too.
*
*/
@Override
protected void onNfcPushStateEnabled() {
toast(getString(R.string.nfcBeamAvailableEnabled));
}
/**
*
* NFC was found and enabled in settings, but push is disabled
*
*/
@Override
protected void onNfcPushStateDisabled() {
toast(getString(R.string.nfcBeamAvailableDisabled));
}
/**
*
* NFC beam setting changed since last check. For example, the user enabled
* beam in the wireless settings.
*
*/
@Override
protected void onNfcPushStateChange(boolean enabled) {
if (enabled) {
toast(getString(R.string.nfcBeamAvailableEnabled));
} else {
toast(getString(R.string.nfcBeamAvailableDisabled));
}
}
/**
*
* NFC feature was found and is currently enabled
*
*/
@Override
protected void onNfcStateEnabled() {
toast(getString(R.string.nfcAvailableEnabled));
}
/**
*
* NFC feature was found but is currently disabled
*
*/
@Override
protected void onNfcStateDisabled() {
toast(getString(R.string.nfcAvailableDisabled));
}
/**
*
* NFC setting changed since last check. For example, the user enabled NFC
* in the wireless settings.
*
*/
@Override
protected void onNfcStateChange(boolean enabled) {
if (enabled) {
toast(getString(R.string.nfcAvailableEnabled));
} else {
toast(getString(R.string.nfcAvailableDisabled));
}
}
/**
*
* This device does not have NFC hardware
*
*/
@Override
protected void onNfcFeatureNotFound() {
toast(getString(R.string.noNfcMessage));
}
/**
* An NDEF message was read and parsed
*
* @param message
* the message
*/
@Override
protected void readNdefMessage(Message message) {
if (message.size() > 1) {
toast(getString(R.string.readMultipleRecordNDEFMessage));
} else {
toast(getString(R.string.readSingleRecordNDEFMessage));
}
}
/**
* An empty NDEF message was read.
*
*/
@Override
protected void readEmptyNdefMessage() {
toast(getString(R.string.readEmptyMessage));
}
/**
*
* Something was read via NFC, but it was not an NDEF message.
*
* Handling this situation is out of scope of this project.
*
*/
@Override
protected void readNonNdefMessage() {
toast(getString(R.string.readNonNDEFMessage));
}
// mNfcAdapter = NfcAdapter.getDefaultAdapter(this);
// if (mNfcAdapter == null) {
// / nameTv = (TextView) findViewById(R.id.nameText);
// nameTv.setText("NFC is not available on this device.");
// capTv = (TextView) findViewById(R.id.capText);
// capTv.setText("NFC is not available on this device.");
// codeTv = (TextView) findViewById(R.id.codeText);
// codeTv.setText("NFC is not available on this device.");
// timeTv = (TextView) findViewById(R.id.timeEdit);
// timeTv.setText("NFC is not available on this device.");
// } else {
// mNfcAdapter.setNdefPushMessageCallback(this, this);
// mNfcAdapter.setOnNdefPushCompleteCallback(this, this);
// }
// }
// @Override
// public NdefMessage createNdefMessage(NfcEvent event) {
// String a="\"";
// String b="\"";
// String message1 = a + ssidTv.getText().toString() +"," +
// capTv.getText().toString()+b;
// String message2 = nameTv.getText().toString();
// String message3 = codeTv.getText().toString();
// String message4 = timeTv.getText().toString();
// byte[] textBytes1 = message1.getBytes();
// byte[] textBytes2 = message2.getBytes();
// byte[] textBytes3 = message3.getBytes();
// byte[] textBytes4 = message4.getBytes();
// NdefRecord textRecord1 = new NdefRecord(NdefRecord.TNF_WELL_KNOWN,
// message1.getBytes(), new byte[] {}, textBytes1);
// NdefRecord textRecord2 = new NdefRecord(NdefRecord.TNF_WELL_KNOWN,
// message2.getBytes(), new byte[] {}, textBytes2);
// NdefRecord textRecord3 = new NdefRecord(NdefRecord.TNF_WELL_KNOWN,
// message3.getBytes(), new byte[] {}, textBytes3);
// NdefRecord textRecord4 = new NdefRecord(NdefRecord.TNF_WELL_KNOWN,
// message4.getBytes(), new byte[] {}, textBytes4);
// NdefMessage msg = new NdefMessage(new NdefRecord[] {textRecord1,
// textRecord2, textRecord3, textRecord4,
// NdefRecord.createApplicationRecord("com.nfc.linked") });
// return msg;
// /**
// * Implementation for the OnNdefPushCompleteCallback interface
// */
// @Override
// public void onNdefPushComplete(NfcEvent arg0) {
// mHandler.obtainMessage(MESSAGE_SENT).sendToTarget();
// }
// /** This handler receives a message from onNdefPushComplete */
// private final Handler mHandler = new Handler() {
// @Override
// public void handleMessage(Message msg) {
// switch (msg.what) {
// case MESSAGE_SENT:
// Toast.makeText(getApplicationContext(),
// "Core Device Rules Sent!", Toast.LENGTH_LONG).show();
// break;
// }
// }
// };
// @Override
// public void onNewIntent(Intent intent) {
// setIntent(intent);
// }
// void processIntent(Intent intent) {
// Parcelable[] rawMsgs = intent
// .getParcelableArrayExtra(NfcAdapter.EXTRA_NDEF_MESSAGES);
// NdefMessage msg = (NdefMessage) rawMsgs[0];
// nameTv.setText(new String(msg.getRecords()[0].getPayload()));
// }
@Override
protected void onResume() {
super.onResume();
new LoadContacts().execute(rowID);
}
private class LoadContacts extends AsyncTask<Long, Object, Cursor> {
DatabaseConnector dbConnector = new DatabaseConnector(Tap.this);
@Override
protected Cursor doInBackground(Long... params) {
dbConnector.open();
return dbConnector.getOneContact(params[0]);
}
@Override
protected void onPostExecute(Cursor result) {
super.onPostExecute(result);
result.moveToFirst();
int nameIndex = result.getColumnIndex("name");
int capIndex = result.getColumnIndex("cap");
int codeIndex = result.getColumnIndex("code");
int timeIndex = result.getColumnIndex("time");
int ssidIndex = result.getColumnIndex("ssid");
nameTv.setText(result.getString(nameIndex));
capTv.setText(result.getString(capIndex));
timeTv.setText(result.getString(timeIndex));
codeTv.setText(result.getString(codeIndex));
ssidTv.setText(result.getString(ssidIndex));
result.close();
dbConnector.close();
}
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
super.onCreateOptionsMenu(menu);
MenuInflater inflater = getMenuInflater();
inflater.inflate(R.menu.view_country_menu, menu);
return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
switch (item.getItemId()) {
case R.id.editItem:
Intent addEditContact = new Intent(this, AddEditDevice.class);
// addEditContact.putExtra(CountryList.ROW_ID, rowID);
// addEditContact.putExtra("name", nameTv.getText());
// addEditContact.putExtra("cap", capTv.getText());
// addEditContact.putExtra("code", codeTv.getText());
startActivity(addEditContact);
return true;
case R.id.user1SettingsSave:
Intent Tap = new Intent(this, ViewCountry.class);
startActivity(Tap);
return true;
case R.id.deleteItem:
deleteContact();
return true;
default:
return super.onOptionsItemSelected(item);
}
}
private void deleteContact() {
AlertDialog.Builder alert = new AlertDialog.Builder(Tap.this);
alert.setTitle(R.string.confirmTitle);
alert.setMessage(R.string.confirmMessage);
alert.setPositiveButton(R.string.delete_btn,
new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int button) {
final DatabaseConnector dbConnector = new DatabaseConnector(
Tap.this);
AsyncTask<Long, Object, Object> deleteTask = new AsyncTask<Long, Object, Object>() {
@Override
protected Object doInBackground(Long... params) {
dbConnector.deleteContact(params[0]);
return null;
}
@Override
protected void onPostExecute(Object result) {
finish();
}
};
deleteTask.execute(new Long[] { rowID });
}
});
alert.setNegativeButton(R.string.cancel_btn, null).show();
}
}
CountryList.java
public class CountryList extends ListActivity {
public static final String ROW_ID = "row_id";
private ListView conListView;
private CursorAdapter conAdapter;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
conListView=getListView();
conListView.setOnItemClickListener(viewConListener);
// map each name to a TextView
String[] from = new String[] { "name" };
int[] to = new int[] { R.id.countryTextView };
conAdapter = new SimpleCursorAdapter(CountryList.this, R.layout.country_list, null, from, to);
setListAdapter(conAdapter); // set adapter
}
@Override
protected void onResume()
{
super.onResume();
new GetContacts().execute((Object[]) null);
}
@Override
protected void onStop()
{
Cursor cursor = conAdapter.getCursor();
if (cursor != null)
cursor.deactivate();
conAdapter.changeCursor(null);
super.onStop();
}
private class GetContacts extends AsyncTask<Object, Object, Cursor>
{
DatabaseConnector dbConnector = new DatabaseConnector(CountryList.this);
@Override
protected Cursor doInBackground(Object... params)
{
dbConnector.open();
return dbConnector.getAllContacts();
}
@Override
protected void onPostExecute(Cursor result)
{
conAdapter.changeCursor(result); // set the adapter's Cursor
dbConnector.close();
}
}
@Override
public boolean onCreateOptionsMenu(Menu menu)
{
super.onCreateOptionsMenu(menu);
MenuInflater inflater = getMenuInflater();
inflater.inflate(R.menu.country_menu, menu);
return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item)
{
Intent addContact = new Intent(CountryList.this, AddEditDevice.class);
startActivity(addContact);
return super.onOptionsItemSelected(item);
}
OnItemClickListener viewConListener = new OnItemClickListener()
{
public void onItemClick(AdapterView<?> arg0, View arg1, int arg2,long arg3)
{
Intent viewCon = new Intent(CountryList.this, ViewCountry.class);
viewCon.putExtra(ROW_ID, arg3);
startActivity(viewCon);
}
};
}
logcat的：
04-16 13:37:22.415: E/AndroidRuntime(10285): FATAL EXCEPTION: main
04-16 13:37:22.415: E/AndroidRuntime(10285): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.wifi.demo/com.wifi.demowifi.demo.Tap}: java.lang.NullPointerException
04-16 13:37:22.415: E/AndroidRuntime(10285): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2180)
04-16 13:37:22.415: E/AndroidRuntime(10285): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2230)
04-16 13:37:22.415: E/AndroidRuntime(10285): at android.app.ActivityThread.access$600(ActivityThread.java:141)
04-16 13:37:22.415: E/AndroidRuntime(10285): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1234)
04-16 13:37:22.415: E/AndroidRuntime(10285): at android.os.Handler.dispatchMessage(Handler.java:99)
04-16 13:37:22.415: E/AndroidRuntime(10285): at android.os.Looper.loop(Looper.java:137)
04-16 13:37:22.415: E/AndroidRuntime(10285): at android.app.ActivityThread.main(ActivityThread.java:5041)
04-16 13:37:22.415: E/AndroidRuntime(10285): at java.lang.reflect.Method.invokeNative(Native Method)
04-16 13:37:22.415: E/AndroidRuntime(10285): at java.lang.reflect.Method.invoke(Method.java:511)
04-16 13:37:22.415: E/AndroidRuntime(10285): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
04-16 13:37:22.415: E/AndroidRuntime(10285): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560)
04-16 13:37:22.415: E/AndroidRuntime(10285): at dalvik.system.NativeStart.main(Native Method)
04-16 13:37:22.415: E/AndroidRuntime(10285): Caused by: java.lang.NullPointerException
04-16 13:37:22.415: E/AndroidRuntime(10285): at com.wifi.demo.Tap.onCreate(Tap.java:75)
04-16 13:37:22.415: E/AndroidRuntime(10285): at android.app.Activity.performCreate(Activity.java:5104)
04-16 13:37:22.415: E/AndroidRuntime(10285): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1080)
04-16 13:37:22.415: E/AndroidRuntime(10285): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2144)
04-16 13:37:22.415: E/AndroidRuntime(10285): ... 11 more
04-16 13:37:25.315: D/libEGL(10339): loaded /system/lib/egl/libEGL_tegra.so
04-16 13:37:25.345: D/libEGL(10339): loaded /system/lib/egl/libGLESv1_CM_tegra.so
04-16 13:37:25.355: D/libEGL(10339): loaded /system/lib/egl/libGLESv2_tegra.so
04-16 13:37:25.385: D/OpenGLRenderer(10339): Enabling debug mode 0
答案 0 :(得分：0)
似乎当你开始第二项活动时，你没有通过你的意图传递任何数据
为了使其更清晰，您必须执行与调用“ViewCountry”时相同的操作
Intent viewCon = new Intent(CountryList.this, ViewCountry.class);
viewCon.putExtra(ROW_ID, arg3);
startActivity(viewCon);