How to be notified on wifi network status change?

Question

I am writing an app that connects to a telnet server via wifi. I have a service that manages the socket connection. It all works fine, but when the phone sleeps it disconnects the wifi radio, which causes the socket connection to break (and throws a SocketException).

I feel like I should be able to set up a a broadcast receiver whose onResume() method is called when the wifi network connection is lost, and that would allow me to gracefully shut down the socket, and re-open it if the network is immediately re-connected. But I can't find anything like that in the doc or via searching.

Service code is here if you want it, thanks for the help, I really appreciate it!

package com.wingedvictorydesign.LightfactoryRemote;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.OutputStream;
import java.net.InetSocketAddress;
import java.net.Socket;
import java.net.SocketException;
import java.net.SocketTimeoutException;
import android.app.Notification;
import android.app.NotificationManager;
import android.app.PendingIntent;
import android.app.Service;
import android.content.Intent;
import android.os.IBinder;
import android.os.RemoteCallbackList;
import android.os.RemoteException;
import android.text.Editable;
import android.util.Log;
import android.widget.Toast;
import android.os.Debug;

/**
 * @author Max
 */
public class TelnetService extends Service {

    private final int DISCONNECTED = 0;
    private final int CONNECTED = 1;
    // place notifications in the notification bar
    NotificationManager mNM;
    protected InputStream in;
    protected OutputStream out;
    protected Socket socket;
    // the socket timeout, to prevent blocking if the server connection is lost.
    protected final int SO_TIMEOUT = 250;
    // holds the incoming stream from socket until it is ready to be read.
    BufferedReader inputBuffer;
    final RemoteCallbackList<TelnetServiceCallback> mCallbacks =
            new RemoteCallbackList<TelnetServiceCallback>();

    @Override
    public void onCreate() {
        super.onCreate();
        Log.d("LightfactoryRemote", "TelnetService onCreate()");
        mNM = (NotificationManager) getSystemService(NOTIFICATION_SERVICE);
    }// end onCreate()

    @Override
    public void onDestroy() {
        super.onDestroy();
        Log.d("LightfactoryRemote", "TelnetService onDestroy()");
        // Cancel the persistent notification, if it hasn't been already.
        mNM.cancel(R.string.telnet_service_connected);
    }// end onDestroy()

    @Override
    public IBinder onBind(Intent intent) {
        Log.d("LightfactoryRemote", "TelnetService onBind()");
        return mBinder;
    }

    @Override
    public boolean onUnbind(Intent intent) {
        super.onUnbind(intent);
        Log.d("LightfactoryRemote", "TelnetService onUnBind()");
        return true;
    }

    @Override
    public void onStart(Intent intent, int startId) {
        super.onStart(intent, startId);
        Log.d("TelnetService", "TelnetService onStart()");
    }

    private final TelnetServiceInterface.Stub mBinder =
            new TelnetServiceInterface.Stub() {

        public void registerCallback(TelnetServiceCallback cb) {
            if (cb != null) mCallbacks.register(cb);
        }

        public void unregisterCallback(TelnetServiceCallback cb) {
            if (cb != null) mCallbacks.unregister(cb);
        }

        public String connectToTelnet(String Host, int Port)
                throws RemoteException {
            // android.os.Debug.waitForDebugger();
            String hostInfo = null;
            try {
                socket = new java.net.Socket();
                socket.setSoTimeout(SO_TIMEOUT);
                socket.connect(new InetSocketAddress(Host, Port), 10000); //setup
                // the port with a timeout of 10sec.
                out = socket.getOutputStream();
                /*
                 * in is wrapped in a reader, then in a Buffered reader. This is
                 * supposedly better for performance, and allows us to read a
                 * line at a time using the readLine() method.
                 */
                inputBuffer = new BufferedReader(new InputStreamReader(
                    socket.getInputStream()));
            } catch (java.io.IOException e) {
                Log.d("TelnetService.java", "Connection failed! " + e);
                /*
                 * if the connection fails, return null for serverResponse,
                 * which will be handled appropriately on the client side.
                 */
                return hostInfo;
            }
            // now that the command has been sent, read the response.
            hostInfo = readBuffer();
            Log.d("TelnetService.java", hostInfo);
            // notify the user that we are connected
            showNotification(CONNECTED, Host, Port);
            return hostInfo;
        }// end connectToTelnet

        /**
         * Tests for a currently active connection. Three cases must be
         * distinguished. 1. A connection attempt has not been made. Return
         * false. 2. A connection attempt has been made, and socket is
         * initialized, but no connection is active. isConnected() returns
         * false. 3. A connection is active. isConnected() returns true.
         */
        public boolean areYouThere() {
            if (socket != null) {
                boolean connectStatus = socket.isConnected();
                return connectStatus;
            } else {
                return false;
            }
        }// end areYouThere

        public void disconnect() {
            try {
                if (inputBuffer != null) {
                    inputBuffer.close();
                }
                if (socket != null) {
                    socket.close();
                }
            } catch (IOException e) {}
            // Cancel the persistent notification.
            mNM.cancel(R.string.telnet_service_connected);
        }// end disconnect()

        /**
         * send the string to the telnet server, and return the response from
         * server If the connection is lost, an IOException results, so return
         * null to be handled appropriately on the client-side.
         * 
         * @throws RemoteException
         */
        public String sendToTelnet(String toTelnet) throws RemoteException {
            if (out == null) {
                /*
                 * if out is still null, no connection has been made. Throw
                 * RemoteException to be handled on the client side.
                 */
                throw new RemoteException();
            } else {
                byte arr[];
                arr = (toTelnet + "\r" + "\n").getBytes();
                try {
                    out.write(arr);
                    // now that the command has been sent, read the response.
                    String serverResponse = readBuffer();
                    return serverResponse;
                } catch (IOException e) {
                    /*
                     * if a connection was made, but then lost, we end up here.
                     * throw a Remoteexception for handling by the client.
                     */
                    Log.d("TelnetService", "IO exception" + e);
                    disconnect();
                    throw new RemoteException();
                }
            }// end else
        }// end sendToTelnet
    };// end ConnectService.Stub class

    public String readBuffer() {
        StringBuilder serverResponse = new StringBuilder();
        int character;
        try {
            // keep reading new lines into line until there are none left.
            while (inputBuffer.ready()) {
                /*
                 * as each character is read, append it to serverResponse,
                 * throwing away the carriage returns (which read as glyphs),
                 * and the ">" prompt symbols.
                 */
                character = inputBuffer.read();
                if ((character != 13) && (character != 62)) {
                    serverResponse.append((char) character);
                }
            }
        }// end try
        catch (SocketTimeoutException e) {
            Log.d("TelnetService read()", "SocketTimeoutException");
        } catch (IOException e) {
            Log.d("TelnetService read()", "read() IO exception" + e);
        }
        return serverResponse.toString();
    }

    /**
     * Show a notification while this service is running.
     */
    private void showNotification(int event, String Host, int Port) {
        // In this sample, we'll use the same text for the ticker and the
        // expanded notification
        CharSequence notificationText = "Connected to " + Host + " : " + Port;
        // Set the icon, scrolling text and timestamp
        Notification notification = new Notification(
            R.drawable.notbar_connected, notificationText,
            System.currentTimeMillis());
        // set the notification not to clear when the user hits
        // "Clear All Notifications"
        notification.flags |= Notification.FLAG_NO_CLEAR;
        // The PendingIntent to launch our activity if the user selects this
        // notification
        PendingIntent contentIntent = PendingIntent.getActivity(this, 0,
            new Intent(this, LightfactoryRemote.class), 0);
        // Set the info for the views that show in the notification panel.
        notification.setLatestEventInfo(this,
            getText(R.string.telnet_service_connected), notificationText,
            contentIntent);
        // Send the notification.
        // We use a string id because it is a unique number. We use it later to
        // cancel.
        mNM.notify(R.string.telnet_service_connected, notification);
    }// end showNotification()
} // end TelnetConnection

Answer 1

Register a BroadcastReceiver for ConnectivityManager.CONNECTIVITY_ACTION. In the onReceive handler you can call NetworkInfo info = (NetworkInfo) intent.getParcelableExtra(ConnectivityManager.EXTRA_NETWORK_INFO) and then info.getType() and check for ConnectivityManager.TYPE_WIFI and do what you want then. :)