嗨，这是我的 java 文件......我正在开发一个 nfc writer 应用程序......下面是我的 java 代码文件
包com.example.nfc_tag_writer；
import android.app.Activity;
import android.content.Intent;
import android.content.SharedPreferences.Editor;
import android.nfc.NdefMessage;
import android.nfc.NdefRecord;
import android.nfc.NfcAdapter;
import android.nfc.NfcAdapter.CreateNdefMessageCallback;
import android.nfc.NfcAdapter.OnNdefPushCompleteCallback;
import android.nfc.NfcEvent;
import android.os.Bundle;
import android.os.Handler;
import android.os.Message;
import android.view.Menu;
import android.view.MenuItem;
import android.widget.EditText;
import android.widget.Toast;
import java.nio.charset.Charset;
public class SendTextViaNFCActivity extends Activity implements CreateNdefMessageCallback, OnNdefPushCompleteCallback {
private static final int MESSAGE_SENT = 1;
String CURSOR_HERE;
String SAVED_TEXT;
String beamText;
private final Handler mHandler;
NfcAdapter mNfcAdapter;
EditText myText;
class AnonymousClass_1 extends Handler {
final /* synthetic */ SendTextViaNFCActivity this$0;
AnonymousClass_1(SendTextViaNFCActivity r1_SendTextViaNFCActivity) {
super();
this$0 = r1_SendTextViaNFCActivity;
}
public void handleMessage(Message msg) {
switch(msg.what) {
case MESSAGE_SENT:
Toast.makeText(this$0.getApplicationContext(), "Message sent!", MESSAGE_SENT).show();
}
}
}
public SendTextViaNFCActivity() {
super();
SAVED_TEXT = "SAVED_TEXT";
CURSOR_HERE = "###CURSOR_HERE###";
beamText = "";
mHandler = new AnonymousClass_1(this);
}
public NdefRecord createMimeRecord(String mimeType, byte[] payload) {
return new NdefRecord((short) 2, mimeType.getBytes(Charset.forName("US-ASCII")), new byte[0], payload);
}
public NdefMessage createNdefMessage(NfcEvent event) {
NdefRecord[] r2_NdefRecord_A = new NdefRecord[2];
r2_NdefRecord_A[0] = createMimeRecord("application/com.example.android.beam", myText.getText().toString().getBytes());
r2_NdefRecord_A[1] = NdefRecord.createApplicationRecord("diewland.nfc.text");
return new NdefMessage(r2_NdefRecord_A);
}
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.send_text_via_nfc);
myText = (EditText) findViewById(R.id.my_text);
mNfcAdapter = NfcAdapter.getDefaultAdapter(this);
if (mNfcAdapter == null) {
myText.setText("NFC is not available on this device.");
myText.setEnabled(false);
}
mNfcAdapter.setNdefPushMessageCallback(this, this, new Activity[0]);
mNfcAdapter.setOnNdefPushCompleteCallback(this, this, new Activity[0]);
}
public boolean onCreateOptionsMenu(Menu menu) {
if (mNfcAdapter == null) {
return super.onCreateOptionsMenu(menu);
} else {
getMenuInflater().inflate(R.menu.options, menu);
return true;
}
}
public void onNdefPushComplete(NfcEvent arg0) {
mHandler.obtainMessage(MESSAGE_SENT).sendToTarget();
}
public void onNewIntent(Intent intent) {
setIntent(intent);
}
public boolean onOptionsItemSelected(MenuItem item) {
switch(item.getItemId()) {
case R.id.menu_settings:
startActivity(new Intent("android.settings.NFCSHARING_SETTINGS"));
return true;
case R.id.menu_reset:
myText.setText("");
return true;
case R.id.menu_share:
if (!"".equals(myText.getText().toString())) {
Intent sendIntent = new Intent();
sendIntent.setAction("android.intent.action.SEND");
sendIntent.putExtra("android.intent.extra.TEXT", myText.getText().toString());
sendIntent.setType("text/plain");
startActivity(Intent.createChooser(sendIntent, "Share via"));
return true;
} else {
return true;
}
}
return super.onOptionsItemSelected(item);
}
protected void onPause() {
super.onPause();
myText.getText().insert(myText.getSelectionStart(), CURSOR_HERE);
Editor editor = getPreferences(0).edit();
editor.putString(SAVED_TEXT, myText.getText().toString());
editor.commit();
}
public void onResume() {
super.onResume();
Intent intent = getIntent();
String type = intent.getType();
if (!"android.intent.action.SEND".equals(intent.getAction()) || type == null) {
if ("android.nfc.action.NDEF_DISCOVERED".equals(getIntent().getAction())) {
processIntent(getIntent());
}
String restoredText = getPreferences(0).getString(SAVED_TEXT, null);
if (restoredText != null) {
myText.setText(restoredText.replaceAll(CURSOR_HERE, beamText));
}
} else if ("text/plain".equals(type)) {
myText.setText(intent.getStringExtra("android.intent.extra.TEXT"));
}
myText.setSelection(myText.getText().length());
}
void processIntent(Intent intent) {
beamText = new String(((NdefMessage) intent.getParcelableArrayExtra("android.nfc.extra.NDEF_MESSAGES")[0]).getRecords()[0].getPayload());
}
}
我收到以下错误
03-19 08:09:56.989: V/NFC(767): this device does not have NFC support
03-19 08:09:56.999: D/AndroidRuntime(767): Shutting down VM
03-19 08:09:56.999: W/dalvikvm(767): threadid=1: thread exiting with uncaught exception (group=0x414c4700)
03-19 08:09:57.029: E/AndroidRuntime(767): FATAL EXCEPTION: main
03-19 08:09:57.029: E/AndroidRuntime(767): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.nfc_tag_writer/com.example.nfc_tag_writer.SendTextViaNFCActivity}: java.lang.NullPointerException
03-19 08:09:57.029: E/AndroidRuntime(767): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2211)
03-19 08:09:57.029: E/AndroidRuntime(767): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2261)
03-19 08:09:57.029: E/AndroidRuntime(767): at android.app.ActivityThread.access$600(ActivityThread.java:141)
03-19 08:09:57.029: E/AndroidRuntime(767): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1256)
03-19 08:09:57.029: E/AndroidRuntime(767): at android.os.Handler.dispatchMessage(Handler.java:99)
03-19 08:09:57.029: E/AndroidRuntime(767): at android.os.Looper.loop(Looper.java:137)
03-19 08:09:57.029: E/AndroidRuntime(767): at android.app.ActivityThread.main(ActivityThread.java:5103)
03-19 08:09:57.029: E/AndroidRuntime(767): at java.lang.reflect.Method.invokeNative(Native Method)
03-19 08:09:57.029: E/AndroidRuntime(767): at java.lang.reflect.Method.invoke(Method.java:525)
03-19 08:09:57.029: E/AndroidRuntime(767): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:737)
03-19 08:09:57.029: E/AndroidRuntime(767): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
03-19 08:09:57.029: E/AndroidRuntime(767): at dalvik.system.NativeStart.main(Native Method)
03-19 08:09:57.029: E/AndroidRuntime(767): Caused by: java.lang.NullPointerException
03-19 08:09:57.029: E/AndroidRuntime(767): at com.example.nfc_tag_writer.SendTextViaNFCActivity.onCreate(SendTextViaNFCActivity.java:75)
03-19 08:09:57.029: E/AndroidRuntime(767): at android.app.Activity.performCreate(Activity.java:5133)
03-19 08:09:57.029: E/AndroidRuntime(767): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
03-19 08:09:57.029: E/AndroidRuntime(767): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2175)
03-19 08:09:57.029: E/AndroidRuntime(767): ... 11 more
请谁能帮帮我 我在 logcat 中收到错误...我无法修复它们...应用程序不幸地停止了崩溃
最佳答案
您检查了mNfcAdapter 是否为null，但即使是，之后仍尝试访问它。尝试移动这些行
mNfcAdapter.setNdefPushMessageCallback(this, this, new Activity[0]);
mNfcAdapter.setOnNdefPushCompleteCallback(this, this, new Activity[0]);
到前面的if的else中:
if (mNfcAdapter == null) {
myText.setText("NFC is not available on this device.");
myText.setEnabled(false);
} else {
mNfcAdapter.setNdefPushMessageCallback(this, this, new Activity[0]);
mNfcAdapter.setOnNdefPushCompleteCallback(this, this, new Activity[0]);
}
关于java - NFC 编写器的 Android 代码，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/22505722/