Problem: Android's isConnected() used to get current state of WiFi often returns false even when the device is connected

My Android app can only function with WiFi connected to the Internet. Thus, I use the following code to check if the device is connected:

ConnectivityManager conMgr = (ConnectivityManager)getSystemService(Activity.CONNECTIVITY_SERVICE);
boolean wifi = conMgr.getNetworkInfo(ConnectivityManager.TYPE_WIFI).isConn开发者_如何学编程ected();

However, very often when the application is launched and WiFi connected to the Internet, I get the notification that is only shown when wifi = false. Have I missed something, or the check is not that accurate?

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My project also relies on Wifi (although I use a private network). The following is my code for setting up a Wifi connection on start up:

private void initWIFI (WifiManager wifiMgr, String SSID, String key)
{
    WifiInfo curr;
    if (null == (curr = wifiMgr.getConnectionInfo()))  // Get current wifi state
    {
        joinNetwork (wifiMgr, SSID, key);
    }
    else switch (curr.getSupplicantState())
    {
        case DISCONNECTED:
        case DORMANT:
        case INACTIVE:
        case SCANNING:
            joinNetwork (wifiMgr, SSID, key);
            break;

        default:
            if (!curr.getSSID().equals (SSID))
                joinNetwork (wifiMgr, SSID, key);
    }

    while (wifiMgr.getConnectionInfo().getIpAddress() == 0)
    {
        try
        {
            Thread.sleep (1000);
        }
        catch (Exception e)
        { }
    }
}

/**This method is used to join the proper WiFi network when necessary.  Normally,
 * the Android retains network configuration and it is not necessary to manually
 * re-join the desired network on software startup. However, when it is determined
 * that the Android is not currently attached to the proper network, this function
 * is used to correct that situation. */
private void joinNetwork (WifiManager wifiMgr, String SSID, String key)
{
    try
    {
        WifiConfiguration wc         = new WifiConfiguration();

        wc.allowedAuthAlgorithms.set (WifiConfiguration.AuthAlgorithm.OPEN);
        wc.allowedAuthAlgorithms.set (WifiConfiguration.AuthAlgorithm.SHARED);

        wc.allowedGroupCiphers.set   (WifiConfiguration.GroupCipher.WEP40);
        wc.allowedGroupCiphers.set   (WifiConfiguration.GroupCipher.WEP104);

        wc.allowedKeyManagement.set  (WifiConfiguration.KeyMgmt.NONE);

        wc.allowedPairwiseCiphers.set (WifiConfiguration.PairwiseCipher.TKIP);
        wc.allowedPairwiseCiphers.set (WifiConfiguration.PairwiseCipher.CCMP);

        wc.allowedProtocols.set      (WifiConfiguration.Protocol.WPA);
        wc.allowedProtocols.set      (WifiConfiguration.Protocol.RSN);

        wc.hiddenSSID                = false;
        wc.priority                  = 32;

        wc.SSID                      = "\"" + SSID + "\"";
        wc.status                    = WifiConfiguration.Status.ENABLED;

        wc.wepKeys[0]                = key;
        wc.wepTxKeyIndex             = 0;

        int netID;                   
        if (-1 == (netID             = wifiMgr.addNetwork (wc)))
        {
            listener.lostConnection (true);
        }
        else
        {
            wifiMgr.enableNetwork (netID, true);
            Thread.sleep (5000);  // Delay to allow the DHCP process to work
        }
    }
    catch (Exception e)
    {
        listener.lostConnection (true);
    }
}

It should be pointed out that I always use the same wireless access point, and the code in joinNetwork() is specifically configured for it, so if your configuration needs to be more flexible, then your solution may be more complex. Sadly, I do not remember the web site where I found the starting point for this code, but it didn't take a ton of Googling to find it. Finally, I'm pretty sure your application needs to have the ACCESS_WIFI_STATE and CHANGE_WIFI_STATE permissions.

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I use code like this:

public static String getCurrentSsid(Context context) {
  final WifiInfo wifiInfo = getCurrentWifiInfo(context);
  if (wifiInfo != null && !StringUtil.isBlank(wifiInfo.getSSID())) {
    return wifiInfo.getSSID();
  }
  return null;
}

public static WifiInfo getCurrentWifiInfo(Context context) {
  final ConnectivityManager connManager = (ConnectivityManager) context.getSystemService(Context.CONNECTIVITY_SERVICE);
  final NetworkInfo networkInfo = connManager.getNetworkInfo(ConnectivityManager.TYPE_WIFI);
  if (networkInfo != null && networkInfo.isConnected()) {
    final WifiManager wifiManager = (WifiManager) context.getSystemService(Context.WIFI_SERVICE);
    return wifiManager.getConnectionInfo();
  }

  return null;
}

At the same time be aware of this two issues 19078 and 3641.