Android WiFi BroadCast Lock

If you want to get the broadcast IP address from a wifi access point you must first request a wifi multicast lock on the device. Android by default filters out UDP broadcast packets.

Follow these steps:

 1. first add the following to your android Manifest.xml file:



  2. Second copy this method into your activity or service class: 

public void getMultiCastLock() {
 WifiManager wim= (WifiManager) _androidContext.getSystemService(Context.WIFI_SERVICE);
 /* Turn off multicast filter */ 
_mcastLock = wim.createMulticastLock(Context.WIFI_SERVICE);
 if(!_mcastLock.isHeld()){
  _mcastLock.acquire();
 }
 }
 *NOTE:replace _androidContext with your local context object;

 3. Copy this method and call it after you acquire the lock

public String getBroadcastAddress() {
 InetAddress currentInetAddress = null;
 String returnValue = "";
 WifiManager myWifiManager = (WifiManager) _androidContext.getSystemService(Context.WIFI_SERVICE);
 DhcpInfo myDhcpInfo = myWifiManager.getDhcpInfo(); 
if (myDhcpInfo == null) {
 System.out.println("Could not get broadcast address");
 return null;
 }
 int broadcast = (myDhcpInfo.ipAddress & myDhcpInfo.netmask) | ~myDhcpInfo.netmask; byte[] quads = new byte[4];
 for (int k = 0; k < 4; k++)
 quads[k] = (byte) ((broadcast >> k * 8) & 0xFF);
 try {
 currentInetAddress= InetAddress.getByAddress(quads);
 } catch (Exception e) {
 }
 if(currentInetAddress != null){ returnValue = currentInetAddress.toString().substring(1);
 }
 return returnValue;
 }

 4. After you are finished. You must release the lock.