无法在恢复时启动Activity ComponentInfo

Question

My app works fine but when the app goes to the background it crashes when it should resume. As you can see in the source code I log the onStart, onStop etcetera events.

In my log I can see onStart, onResume when I start the app. When I press the back-key I see: onStop, STOP, onPause and onDestroy.

When I try to restart the app it crashes immediately, no further messages are in the log except 'unable to start Activity ComponentInfo java lang.NullPointerException.

How can I prevent this?

public class Start extends Activity {

private Handler handler = new Handler();
private ArrayList<String> discussionThread;
private EditText textMessage;

private ListView listview;

private ConnectionConfiguration config;
private Presence presence;
private MultiUserChat muc;
private DiscussionHistory history;
private PacketFilter filter;
private MyCustomAdapter discussionThreadAdapter;
private XMPPConnection connection;


/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);
    try {
        initConnection();
    } catch (XMPPException e) {
        e.printStackTrace();
    }

    final EditText textMessage = (EditText) this.findViewById(R.id.message);        
    listview = (ListView) this.findViewById(R.id.list);

    discussionThread = new ArrayList<String>();
    discussionThreadAdapter = new MyCustomAdapter();
    listview.setAdapter(discussionThreadAdapter);

    Button send = (Button) this.findViewById(R.id.send);
    send.setOnClickListener(new View.OnClickListener() {
        public void onClick(View view) {
            String text = textMessage.getText().toString();

            Message msg = new Message(ROOM, Message.Type.groupchat);
            msg.setBody(text);
            connection.sendPacket(msg);
            discussionThreadAdapter.notifyDataSetChanged();
            textMessage.setText("");
        }
    });


    textMessage.setOnKeyListener(new OnKeyListener()
    {
        public boolean onKey(View v, int keyCode, KeyEvent event)
        {
            if (event.getAction() == KeyEvent.ACTION_DOWN)
            {
                switch (keyCode)
                {
                    case KeyEvent.KEYCODE_DPAD_CENTER:
                    case KeyEvent.KEYCODE_ENTER:
                        SendText();
                        return true;
                    default:
                        break;
                }
            }
            return false;
        }
    });
}


private void initConnection() throws XMPPException {
    config = new ConnectionConfiguration(SERVER_HOST, SERVER_PORT, SERVICE_NAME);
    connection = new XMPPConnection(config);
    connection.connect();
    connection.login(LOGIN, PASSWORD);
    presence = new Presence(Presence.Type.available);

    connection.sendPacket(presence);

    muc = new MultiUserChat(connection, ROOM);
    history = new DiscussionHistory();

    history.setMaxStanzas(25);

    muc.join(LOGIN, PASSWORD, history, SmackConfiguration.getPacketReplyTimeout());

    filter = new MessageTypeFilter(Message.Type.groupchat);

    connection.addPacketListener(new PacketListener() {

        public void processPacket(Packet packet) {
            Message message = (Message) packet;
            if (message.getBody() != null) {
                String fromName = message.getFrom().substring(48);
                String nieuweRegel = fromName + ": " + message.getBody();

                fromName = fromName.toUpperCase();

                if (fromName.equals(LOGIN.toUpperCase())) {
                    discussionThreadAdapter.addVanMijItem(nieuweRegel);
                } else {
                    discussionThreadAdapter.addVanAnderItem(nieuweRegel);
                }

            }
        }
    }, filter);

}

private void Notify() {
    discussionThreadAdapter.notifyDataSetChanged();
    listview.setSelection(discussionThreadAdapter.getCount());
}

private class MyCustomAdapter extends BaseAdapter {

    private static final int BERICHT_VAN_ANDER = 0;
    private static final int BERICHT_VAN_MIJ = 1;
    private static final int TYPE_MAX_COUNT = BERICHT_VAN_MIJ + 1;

    private LayoutInflater mInflater;

    private TreeSet<Integer> mySet = new TreeSet<Integer>();

    public MyCustomAdapter() {
        mInflater = (LayoutInflater)getSystemService(Context.LAYOUT_INFLATER_SERVICE);
    }

    public void addVanAnderItem(final String item) {
        discussionThread.add(item);
        handler.post(new Runnable() {
            public void run() {
                Notify();
            }
        });

    }

    public void addVanMijItem(final String item) {
        discussionThread.add(item);
        mySet.add(discussionThread.size() - 1);
        handler.post(new Runnable() {
            public void run() {
                Notify();
            }
        });
    }

    @Override
    public int getItemViewType(int position) {
        return mySet.contains(position) ? BERICHT_VAN_MIJ : BERICHT_VAN_ANDER;
    }

    @Override
    public int getViewTypeCount() {
        return TYPE_MAX_COUNT;
    }

    @Override
    public int getCount() {
        return discussionThread.size();
    }

    @Override
    public String getItem(int position) {
        return discussionThread.get(position);
    }

    @Override
    public long getItemId(int position) {
        return position;
    }

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        ViewHolder holder = null;
        int type = getItemViewType(position);
        if (convertView == null) {
            holder = new ViewHolder();
            switch (type) {
                case BERICHT_VAN_ANDER:
                    convertView = mInflater.inflate(R.layout.bericht_van_ander_item, null);
                    holder.textView = (TextView)convertView.findViewById(R.id.textline);
                    break;
                case BERICHT_VAN_MIJ:
                    convertView = mInflater.inflate(R.layout.bericht_van_mij_item, null);
                    holder.textView = (TextView)convertView.findViewById(R.id.textline);
                    break;
            }
            convertView.setTag(holder);
        } else {
            holder = (ViewHolder)convertView.getTag();
        }
        holder.textView.setText(discussionThread.get(position));
        return convertView;
    }

}

public static class ViewHolder {
    public TextView textView;
}

private void SendText() {

    InputMethodManager imm = (InputMethodManager)getSystemService(Context.INPUT_METHOD_SERVICE);
    imm.hideSoftInputFromWindow(textMessage.getWindowToken(), 0);

    String text = textMessage.getText().toString();

    Message msg = new Message(ROOM, Message.Type.groupchat);
    msg.setBody(text);
    connection.sendPacket(msg);
    textMessage.setText("");
}

public void onStart() {
    super.onStart();
    Log.i("CONN", "onStart");
    startConnection();
}

public void onRestart() {
    super.onRestart();
    Log.i("CONN", "onReStart");
    startConnection();
}

public void onResume() {
    super.onResume();
    Log.i("CONN", "onResume");
    startConnection();
}

public void onPause() {
    super.onPause();
    Log.i("CONN", "onPause");
    stopConnection();

}

public void onStop() {
    super.onStop();
    Log.i("CONN", "onStop");
    stopConnection();
}

public void onDestroy() {
    super.onDestroy();
    Log.i("CONN", "onDestroy");
    stopConnection();
}

private void stopConnection() {

    if (connection != null) {

        Log.i("CONN", "STOP");

        connection.disconnect(presence);

        connection = null;
        filter = null;
        history = null;
        muc = null;
        presence = null;
        config = null;
        discussionThreadAdapter = null;


    }

}

private void startConnection() {

    if (connection.isConnected() ) {

    } else {

        Log.i("CONN", "START");

        try {
            initConnection();
        } catch (XMPPException e) {
            e.printStackTrace();
        }
    }
}

}

OK I changed the following:

   private void startConnection() {

    if (connection != null ) {

        Log.i("CONN", "RUNNING");

    } else {

        Log.i("CONN", "START");

        try {
            initConnection();
        } catch (XMPPException e) {
            e.printStackTrace();
        }
    }
}

I start the app, everything works fine. Log:

05-12 08:40:21.743: D/AndroidRuntime(491): >>>>>>>>>>>>>> AndroidRuntime START <<<<<<<<<<<<<< 05-12 08:40:21.743: D/AndroidRuntime(491): CheckJNI is ON

05-12 08:40:22.065: D/AndroidRuntime(491): --- registering native functions ---

05-12 08:40:23.353: D/AndroidRuntime(491): Shutting down VM

05-12 08:40:23.363: D/dalvikvm(491): Debugger has detached; object registry had 1 entries

05-12 08:40:23.393: I/AndroidRuntime(491): NOTE: attach of thread 'Binder Thread #3' failed

05-12 08:40:24.184: D/AndroidRuntime(499): >>>>>>>>>>>>>> AndroidRuntime START <<<<<<<<<<<<<<

05-12 08:40:24.184: D/AndroidRuntime(499): CheckJNI is ON

05-12 08:40:24.523: D/AndroidRuntime(499): --- registering native functions ---

05-12 08:40:25.873: I/ActivityManager(70): Starting activity: Intent { act=android.intent.action.MAIN cat=[android.intent.category.LAUNCHER] flg=0x10000000 cmp=nl.yeswecanclinics.chat/.Start }

05-12 08:40:25.965: D/AndroidRuntime(499): Shutting down VM

05-12 08:40:25.973: D/dalvikvm(499): Debugger has detached; object registry had 1 entries

05-12 08:40:26.034: I/AndroidRuntime(499): NOTE: attach of thread 'Binder Thread #3' failed

05-12 08:40:26.105: I/ActivityManager(70): Start proc nl.yeswecanclinics.chat for activity nl.yeswecanclinics.chat/.Start: pid=506 uid=10032 gids={3003, 1015}

05-12 08:40:27.843: I/global(506): Default buffer size used in BufferedReader constructor. It would be better to be explicit if an 8k-char buffer is required.

05-12 08:40:27.843: I/global(506): Default buffer size used in BufferedWriter constructor. It would be better to be explicit if an 8k-char buffer is required.

05-12 08:40:28.294: W/System.err(506): java.security.KeyStoreException: KeyStore jks implementation not found

05-12 08:40:28.294: W/System.err(506): at java.security.KeyStore.getInstance(KeyStore.java:134)

05-12 08:40:28.294: W/System.err(506): at org.jivesoftware.smack.ServerTrustManager.(ServerTrustManager.java:61)

05-12 08:40:28.294: W/System.err(506): at org.jivesoftware.smack.XMPPConnection.proceedTLSReceived(XMPPConnection.java:832)

05-12 08:40:28.304: W/System.err(506): at org.jivesoftware.smack.PacketReader.parsePackets(PacketReader.java:268)

05-12 08:40:28.304: W/System.err(506): at org.jivesoftware.smack.PacketReader.access$000(PacketReader.java:44)

05-12 08:40:28.313: W/System.err(506): at org.jivesoftware.smack.PacketReader$1.run(PacketReader.java:71)

05-12 08:40:29.004: I/global(506): Default buffer size used in BufferedReader constructor. It would be better to be explicit if an 8k-char buffer is required.

05-12 08:40:29.014: I/global(506): Default buffer size used in BufferedWriter constructor. It would be better to be explicit if an 8k-char buffer is required.

05-12 08:40:29.483: D/dalvikvm(506): GC_FOR_MALLOC freed 3668 objects / 280752 bytes in 153ms

05-12 08:40:29.663: I/CONN(506): onStart

05-12 08:40:29.685: I/CONN(506): RUNNING

05-12 08:40:29.685: I/CONN(506): onResume

05-12 08:40:29.693: I/CONN(506): RUNNING

05-12 08:40:30.633: I/ActivityManager(70): Displayed activity nl.yeswecanclinics.chat/.Start: 4712 ms (total 384269 ms)

05-12 08:40:37.114: D/dalvikvm(175): GC_EXPLICIT freed 444 objects / 22064 bytes in 122ms

I PRESS THE BACK BUTTON

05-12 08:41:07.253: W/KeyCharacterMap(506): No keyboard for id 0

05-12 08:41:07.253: W/KeyCharacterMap(506): Using default keymap: /system/usr/keychars/qwerty.kcm.bin

05-12 08:41:07.403: I/CONN(506): onPause

05-12 08:41:07.403: I/CONN(506): STOP

05-12 08:41:07.784: W/InputManagerService(70): Starting input on non-focused client com.android.internal.view.IInputMethodClient$Stub$Proxy@45066cf8 (uid=10032 pid=506)

05-12 08:41:07.804: W/IInputConnectionWrapper(506): showStatusIcon on inactive InputConnection

05-12 08:41:08.173: I/CONN(506): onStop

05-12 08:41:08.173: I/CONN(506): onDestroy

I RESTART THE APP BY CLICKING THE ICON

05-12 08:41:30.583: I/global(506): Default buffer size used in BufferedReader constructor. It would be better to be explicit if an 8k-char buffer is required.

05-12 08:41:30.623: I/global(506): Default buffer size used in BufferedWriter constructor. It would be better to be explicit if an 8k-char buffer is required.

05-12 08:41:31.663: W/System.err(506): java.security.KeyStoreException: KeyStore jks implementation not found

05-12 08:41:31.663: W/System.err(506): at java.security.KeyStore.getInstance(KeyStore.java:134)

05-12 08:41:31.663: W/System.err(506): at org.jivesoftware.smack.ServerTrustManager.(ServerTrustManager.java:61)

05-12 08:41:31.674: W/System.err(506): at org.jivesoftware.smack.XMPPConnection.proceedTLSReceived(XMPPConnection.java:832)

05-12 08:41:31.674: W/System.err(506): at org.jivesoftware.smack.PacketReader.parsePackets(PacketReader.java:268)

05-12 08:41:31.683: W/System.err(506): at org.jivesoftware.smack.PacketReader.access$000(PacketReader.java:44)

05-12 08:41:31.683: W/System.err(506): at org.jivesoftware.smack.PacketReader$1.run(PacketReader.java:71)

05-12 08:41:31.984: I/global(506): Default buffer size used in BufferedReader constructor. It would be better to be explicit if an 8k-char buffer is required.

05-12 08:41:31.994: I/global(506): Default buffer size used in BufferedWriter constructor. It would be better to be explicit if an 8k-char buffer is required.

05-12 08:41:32.043: D/AndroidRuntime(506): Shutting down VM

05-12 08:41:32.043: W/dalvikvm(506): threadid=1: thread exiting with uncaught exception (group=0x4001d800)

05-12 08:41:32.214: D/dalvikvm(506): GC_FOR_MALLOC freed 5507 objects / 388504 bytes in 147ms

05-12 08:41:32.226: D/NativeCrypto(506): Freeing OpenSSL session

05-12 08:41:32.234: E/AndroidRuntime(506): FATAL EXCEPTION: main

05-12 08:41:32.234: E/AndroidRuntime(506): java.lang.RuntimeException: Unable to start activity ComponentInfo{nl.yeswecanclinics.chat/nl.yeswecanclinics.chat.Start}: java.lang.NullPointerException

05-12 08:41:32.234: E/AndroidRuntime(506): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2663)

05-12 08:41:32.234: E/AndroidRuntime(506): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2679)

05-12 08:41:32.234: E/AndroidRuntime(506): at android.app.ActivityThread.access$2300(ActivityThread.java:125)

05-12 08:41:32.234: E/AndroidRuntime(506): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2033)

05-12 08:41:32.234: E/AndroidRuntime(506): at android.os.Handler.dispatchMessage(Handler.java:99)

05-12 08:41:32.234: E/AndroidRuntime(506): at android.os.Looper.loop(Looper.java:123)

05-12 08:41:32.234: E/AndroidRuntime(506): at android.app.ActivityThread.main(ActivityThread.java:4627)

05-12 08:41:32.234: E/AndroidRuntime(506): at java.lang.reflect.Method.invokeNative(Native Method)

05-12 08:41:32.234: E/AndroidRuntime(506): at java.lang.reflect.Method.invoke(Method.java:521)

05-12 08:41:32.234: E/AndroidRuntime(506): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:868) 05-12 08:41:32.234: E/AndroidRuntime(506): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:626)

05-12 08:41:32.234: E/AndroidRuntime(506): at dalvik.system.NativeStart.main(Native Method)

05-12 08:41:32.234: E/AndroidRuntime(506): Caused by: java.lang.NullPointerException

05-12 08:41:32.234: E/AndroidRuntime(506): at org.jivesoftware.smackx.muc.MultiUserChat$1.connectionCreated(MultiUserChat.java:114)

05-12 08:41:32.234: E/AndroidRuntime(506): at org.jivesoftware.smack.XMPPConnection.initConnection(XMPPConnection.java:618)

05-12 08:41:32.234: E/AndroidRuntime(506): at org.jivesoftware.smack.XMPPConnection.connectUsingConfiguration(XMPPConnection.java:565)

05-12 08:41:32.234: E/AndroidRuntime(506): at org.jivesoftware.smack.XMPPConnection.connect(XMPPConnection.java:991)

05-12 08:41:32.234: E/AndroidRuntime(506): at nl.yeswecanclinics.chat.Start.initConnection(Start.java:131)

05-12 08:41:32.234: E/AndroidRuntime(506): at nl.yeswecanclinics.chat.Start.onCreate(Start.java:71)

05-12 08:41:32.234: E/AndroidRuntime(506): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)

05-12 08:41:32.234: E/AndroidRuntime(506): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2627)

05-12 08:41:32.234: E/AndroidRuntime(506): ... 11 more

Answer 1

While Marek's answer is certainly not incorrect (this may in fact be why you are getting a NullPointerException ), one thing I know is that you shouldn't be attempting to make connections on the UI thread. This will inevitably cause your application to crash in the case that it takes more than a couple seconds to make a connection. You should make an AsnycTask and do your connection and status changes there.

Answer 2

You set in stopConnection method null to connection so when you try to do check if(connection.isConnected()) you receive null because you set it. You should check in startConnection method if connection is not null otherwise you must call initConnection method.