Android : Reconnect to Wi-Fi after entering coverage area while screen turned off

Question

I have been struggling with automatically turning on Wi-Fi as soon as the device is within range of an access point without turning on the screen. It has been very frustrati

Answer 1

My scenario is slightly different - I do not hold a wifi lock to begin with (and I am on regular android so I had to translate your method).

Screen off, CPU off, radio dies. Alarm wakes my (wakeful) service up - I hold a (partial) wake lock.

What I want is - if wifi is enabled to connect to the access point it was connected before the radio died - I acquire a wifi lock and I call your function - wakeWifiUp(). When the radio has died (!wifiInfo.IsConnectedOrConnecting is true) I get a network unreachable when I try to connect. I workaround it as in :

public final class NetworkService extends WakefulIntentService {

    // this is an intent service - runs on its own thread - otherwise it would
    // deadlock as I am using it. Moreover it holds a wakelock and woken up by
    // an AlarmManager's Receiver - works reliably
    private BroadcastReceiver mConnectionReceiver;
    private volatile static CountDownLatch latch;

    @Override
    protected void doWakefulWork(Intent intent) {
        WifiLock _wifiLock = null;
        WifiManager wm = (WifiManager) getSystemService(Context.WIFI_SERVICE);
        boolean failedToConnect = true;
        if (wm != null && wm.isWifiEnabled()) {// Don't want to enable it myself
            _wifiLock = wm.createWifiLock(
            /* WifiManager.WIFI_MODE_FULL_HIGH_PERF */0x3, this.getClass()
                .getName() + ".WIFI_LOCK");
            _wifiLock.acquire();
            failedToConnect = !wakeWifiUp();
        }
        if (failedToConnect) {
            if (_wifiLock != null) _wifiLock.release();
            w("No connection !");
            return;
        }
        HttpURLConnection connection = null;
        try {
            connection = connection(); 
        } catch (IOException e) {/* won't throw - it doesn't do much*/}
        OutputStream serverOutputStream = null;
        try {
            serverOutputStream = connection.getOutputStream(); // now
            // this is really where the connection might seriously throw
            // .... Work ....
        } catch (IOException e) {
            w("IOException sending data " + e.getMessage());
            // I get here : Network unreachable when radio dies
        } finally {
            if (_wifiLock != null) _wifiLock.release();
            if (connection != null) connection.disconnect();
        }
    }

    private HttpURLConnection connection() throws MalformedURLException,
            IOException {
        HttpURLConnection connection = (HttpURLConnection) new URL("localhost")
            .openConnection();
        connection.setDoOutput(true); // triggers POST
        connection.setRequestProperty("Connection", "Keep-Alive");
        connection.setRequestProperty("User-Agent",
            "Android Multipart HTTP Client 1.1");
        return connection;
    }

    private boolean wakeWifiUp() {
        ConnectivityManager _androidConnectivityMgr = (ConnectivityManager)
                getSystemService(Context.CONNECTIVITY_SERVICE);
        NetworkInfo wifiInfo = _androidConnectivityMgr
            .getNetworkInfo(ConnectivityManager.TYPE_WIFI);
        WifiManager _wifiManager = (WifiManager)
                getSystemService(Context.WIFI_SERVICE);
        final int wifiState = _wifiManager.getWifiState();
        if (!_wifiManager.isWifiEnabled()
            || wifiState == WifiManager.WIFI_STATE_DISABLED
            || wifiState == WifiManager.WIFI_STATE_DISABLING) {
            // Make sure the Wi-Fi is enabled, required for some devices when
            // enable WiFi does not occur immediately
            d("!_wifiManager.isWifiEnabled()");
            _wifiManager.setWifiEnabled(true);
            // do not enable if not enabled ! FIXME
            return false;
        }
        if (!wifiInfo.isConnectedOrConnecting()) {
            d("Wifi is NOT Connected Or Connecting - "
                + "wake it up and wait till is up");
            // Do not wait for the OS to initiate a reconnect to a Wi-Fi router
            _wifiManager.pingSupplicant();
            if (wifiState == WifiManager.WIFI_STATE_ENABLED) {
                try {
                    // Brute force methods required for some devices
                    _wifiManager.setWifiEnabled(false);
                    _wifiManager.setWifiEnabled(true);
                } catch (SecurityException e) {
                    // Catching exception which should not occur on most
                    // devices. OS bug details at :
                    // https://code.google.com/p/android/issues/detail?id=22036
                }
            }
            _wifiManager.disconnect();
            _wifiManager.startScan();
            _wifiManager.reassociate();
            _wifiManager.reconnect();
            // THIS IS WHAT I DO TO WAIT FOR A CONNECTION
            try {
                mConnectionReceiver = new WifiConnectionMonitor();
                startMonitoringConnection();
                latch = new CountDownLatch(1);
                w("I wait");
                latch.await();
                w("Woke up");
                return true; // made it
            } catch (InterruptedException e) {
                w("Interrupted while waiting for connection", e);
                return false;
            } finally {
                stopMonitoringConnection();
            }
        }
        return true;
    }

    static void downTheLatch() {
        latch.countDown();
    }

    private synchronized void startMonitoringConnection() {
        IntentFilter aFilter = new IntentFilter(
            ConnectivityManager.CONNECTIVITY_ACTION);
        aFilter.addAction(WifiManager.NETWORK_STATE_CHANGED_ACTION);
        registerReceiver(mConnectionReceiver, aFilter);
    }

    private synchronized void stopMonitoringConnection() {
        unregisterReceiver(mConnectionReceiver);
    }

    private final class WifiConnectionMonitor extends BroadcastReceiver {

        @Override
        public void onReceive(Context context, Intent in) {
            String action = in.getAction();
            if (action.equals(WifiManager.NETWORK_STATE_CHANGED_ACTION)) {
                NetworkInfo networkInfo = in
                    .getParcelableExtra(WifiManager.EXTRA_NETWORK_INFO);
                d(networkInfo + "");
                if (networkInfo.isConnected()) {
                    d("Wifi is connected!");
                    NetworkService.downTheLatch(); // HERE THE SERVICE IS WOKEN!
                }
            }
        }
    }
}

Btw not all the tricks in wakeWifiUp() are needed (in my case) and all the !_wifiManager.isWifiEnabled() may be ommited - as I only use the net if enabled by the user. I leave it for completeness.

Recap : in my scenario your method was not enough (if I translated correctly to java and didn't make some silly mistake, which always applies - see also my connection()). I needed to wait for connection to be established - but then all was fine. Not sure still how exactly you were using it - if as I do then the difference might be that you were holding a wifi lock all along

HTC Nexus 1, 2.3.7, Cyanogen mod (don't shoot I've been given it to test).

Will keep you posted