我对 android 应用程序开发非常陌生。我创建了一个结合 GCM 和 Webview 的应用程序。实际上，我复制了代码并根据需要进行了更改。应用程序在 2.3 Gb 中运行良好。在 4 及以上，应用程序意外停止。只是第一次。这是第一次发生。下次继续它的工作正常。
应用程序活动流程就像这样的活动1->活动2->活动3。
Activty2(MainActivity) 将在第二次启动时被跳过。
这是来自 logcat 的错误
10-14 21:54:01.623: V/GCMBaseIntentService(28919): Releasing wakelock
10-14 21:54:01.623: W/dalvikvm(28919): threadid=11: thread exiting with uncaught exception (group=0x41fde2a0)
10-14 21:54:01.633: E/AndroidRuntime(28919): FATAL EXCEPTION: IntentService[GCMIntentService-xxxxxxxx-1]
10-14 21:54:01.633: E/AndroidRuntime(28919): java.lang.NullPointerException: println needs a message
10-14 21:54:01.633: E/AndroidRuntime(28919): at android.util.Log.println_native(Native Method)
10-14 21:54:01.633: E/AndroidRuntime(28919): at android.util.Log.d(Log.java:155)
10-14 21:54:01.633: E/AndroidRuntime(28919): at com.wCityDrugs.GCMIntentService.onRegistered(GCMIntentService.java:29)
10-14 21:54:01.633: E/AndroidRuntime(28919): at com.google.android.gcm.GCMBaseIntentService.handleRegistration(GCMBaseIntentService.java:296)
10-14 21:54:01.633: E/AndroidRuntime(28919): at com.google.android.gcm.GCMBaseIntentService.onHandleIntent(GCMBaseIntentService.java:197)
10-14 21:54:01.633: E/AndroidRuntime(28919): at android.app.IntentService$ServiceHandler.handleMessage(IntentService.java:65)
10-14 21:54:01.633: E/AndroidRuntime(28919): at android.os.Handler.dispatchMessage(Handler.java:99)
10-14 21:54:01.633: E/AndroidRuntime(28919): at android.os.Looper.loop(Looper.java:137)
10-14 21:54:01.633: E/AndroidRuntime(28919): at android.os.HandlerThread.run(HandlerThread.java:60)
10-14 21:54:10.678: V/GCMRegistrar(28919): Unregistering receiver
10-14 21:54:10.683: E/UnRegister Receiver Error(28919): > Receiver not registered: com.google.android.gcm.GCMBroadcastReceiver@42e88d70
这是 GCMIntentService.java
package com.wCityDrugs;
import static com.wCityDrugs.CommonUtilities.SENDER_ID;
import static com.wCityDrugs.CommonUtilities.displayMessage;
import android.app.Notification;
import android.app.NotificationManager;
import android.app.PendingIntent;
import android.content.Context;
import android.content.Intent;
import android.util.Log;
import com.google.android.gcm.GCMBaseIntentService;
public class GCMIntentService extends GCMBaseIntentService {
private static final String TAG = "GCMIntentService";
public GCMIntentService() {
super(SENDER_ID);
}
/**
* Method called on device registered
**/
@Override
protected void onRegistered(Context context, String registrationId) {
Log.i(TAG, "Device registered: regId = " + registrationId);
displayMessage(context, "Your device registred with GCM");
Log.d("NAME", MainActivity.name);
ServerUtilities.register(context, MainActivity.name, MainActivity.email, registrationId);
}
/**
* Method called on device un registred
* */
@Override
protected void onUnregistered(Context context, String registrationId) {
Log.i(TAG, "Device unregistered");
displayMessage(context, getString(R.string.gcm_unregistered));
ServerUtilities.unregister(context, registrationId);
}
/**
* Method called on Receiving a new message
* */
@Override
protected void onMessage(Context context, Intent intent) {
Log.i(TAG, "Received message");
String message = intent.getExtras().getString("price");
displayMessage(context, message);
// notifies user
generateNotification(context, message);
}
/**
* Method called on receiving a deleted message
* */
@Override
protected void onDeletedMessages(Context context, int total) {
Log.i(TAG, "Received deleted messages notification");
String message = getString(R.string.gcm_deleted, total);
displayMessage(context, message);
// notifies user
generateNotification(context, message);
}
/**
* Method called on Error
* */
@Override
public void onError(Context context, String errorId) {
Log.i(TAG, "Received error: " + errorId);
displayMessage(context, getString(R.string.gcm_error, errorId));
}
@Override
protected boolean onRecoverableError(Context context, String errorId) {
// log message
Log.i(TAG, "Received recoverable error: " + errorId);
displayMessage(context, getString(R.string.gcm_recoverable_error,
errorId));
return super.onRecoverableError(context, errorId);
}
/**
* Issues a notification to inform the user that server has sent a message.
*/
private static void generateNotification(Context context, String message) {
int icon = R.drawable.ic_launcher;
long when = System.currentTimeMillis();
NotificationManager notificationManager = (NotificationManager)
context.getSystemService(Context.NOTIFICATION_SERVICE);
Notification notification = new Notification(icon, message, when);
String title = context.getString(R.string.app_name);
Intent notificationIntent = new Intent(context, MainActivity.class);
// set intent so it does not start a new activity
notificationIntent.setFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP |
Intent.FLAG_ACTIVITY_SINGLE_TOP);
PendingIntent intent =
PendingIntent.getActivity(context, 0, notificationIntent, 0);
notification.setLatestEventInfo(context, title, message, intent);
notification.flags |= Notification.FLAG_AUTO_CANCEL;
// Play default notification sound
notification.defaults |= Notification.DEFAULT_SOUND;
//notification.sound = Uri.parse("android.resource://" + context.getPackageName() + "your_sound_file_name.mp3");
// Vibrate if vibrate is enabled
notification.defaults |= Notification.DEFAULT_VIBRATE;
notificationManager.notify(0, notification);
}
}
这是我的 MainActivity.java
package com.wCityDrugs;
import static com.wCityDrugs.CommonUtilities.DISPLAY_MESSAGE_ACTION;
import static com.wCityDrugs.CommonUtilities.EXTRA_MESSAGE;
import static com.wCityDrugs.CommonUtilities.SENDER_ID;
import android.app.Activity;
import android.content.BroadcastReceiver;
import android.content.Context;
import android.content.Intent;
import android.content.IntentFilter;
import android.content.SharedPreferences;
import android.content.SharedPreferences.Editor;
import android.os.AsyncTask;
import android.os.Bundle;
import android.util.Log;
import android.widget.TextView;
import android.widget.Toast;
import com.google.android.gcm.GCMRegistrar;
public class MainActivity extends Activity {
// label to display gcm messages
TextView lblMessage;
// Asyntask
AsyncTask<Void, Void, Void> mRegisterTask;
// Alert dialog manager
AlertDialogManager alert = new AlertDialogManager();
// Connection detector
ConnectionDetector cd;
public static String name;
public static String email;
@Override
public void onCreate(Bundle savedInstanceState) {
SharedPreferences pref = getSharedPreferences("ActivityPREF", Context.MODE_PRIVATE);
if(pref.getBoolean("activity_executed", false)){
Intent intent = new Intent(this, web_index.class);
startActivity(intent);
finish();
} else {
Editor ed = pref.edit();
ed.putBoolean("activity_executed", true);
ed.commit();
}
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
cd = new ConnectionDetector(getApplicationContext());
// Check if Internet present
if (!cd.isConnectingToInternet()) {
// Internet Connection is not present
alert.showAlertDialog(MainActivity.this,
"Internet Connection Error",
"Please connect to working Internet connection", false);
// stop executing code by return
return;
}
// Getting name, email from intent
Intent i = getIntent();
name = i.getStringExtra("name");
email = i.getStringExtra("email");
// Make sure the device has the proper dependencies.
GCMRegistrar.checkDevice(this);
// Make sure the manifest was properly set - comment out this line
// while developing the app, then uncomment it when it's ready.
GCMRegistrar.checkManifest(this);
lblMessage = (TextView) findViewById(R.id.lblMessage);
registerReceiver(mHandleMessageReceiver, new IntentFilter(
DISPLAY_MESSAGE_ACTION));
// Get GCM registration id
final String regId = GCMRegistrar.getRegistrationId(this);
// Check if regid already presents
if (regId.equals("")) {
// Registration is not present, register now with GCM
GCMRegistrar.register(this, SENDER_ID);
} else {
// Device is already registered on GCM
if (GCMRegistrar.isRegisteredOnServer(this)) {
// Skips registration.
Toast.makeText(getApplicationContext(), "Welcome Back", Toast.LENGTH_SHORT).show();
} else {
// Try to register again, but not in the UI thread.
// It's also necessary to cancel the thread onDestroy(),
// hence the use of AsyncTask instead of a raw thread.
final Context context = this;
mRegisterTask = new AsyncTask<Void, Void, Void>() {
@Override
protected Void doInBackground(Void... params) {
// Register on our server
// On server creates a new user
ServerUtilities.register(context, name, email, regId);
return null;
}
@Override
protected void onPostExecute(Void result) {
mRegisterTask = null;
}
};
mRegisterTask.execute(null, null, null);
}
}
}
/**
* Receiving push messages
* */
private final BroadcastReceiver mHandleMessageReceiver = new BroadcastReceiver() {
@Override
public void onReceive(Context context, Intent intent) {
String newMessage = intent.getExtras().getString(EXTRA_MESSAGE);
// Waking up mobile if it is sleeping
WakeLocker.acquire(getApplicationContext());
/**
* Take appropriate action on this message
* depending upon your app requirement
* For now i am just displaying it on the screen
* */
// Showing received message
lblMessage.append(newMessage + "\n");
Toast.makeText(getApplicationContext(), "New Message: " + newMessage, Toast.LENGTH_SHORT).show();
// Releasing wake lock
WakeLocker.release();
}
};
@Override
protected void onDestroy() {
if (mRegisterTask != null) {
mRegisterTask.cancel(true);
}
try {
unregisterReceiver(mHandleMessageReceiver);
GCMRegistrar.onDestroy(this);
} catch (Exception e) {
Log.e("UnRegister Receiver Error", "> " + e.getMessage());
}
super.onDestroy();
}}
谁能指导我摆脱这个错误。