Nullpointerexception getSystemService

Following line will only not result in a nullpointer exception if I'm connected to a WLAN:

ConnectivityManager cm = (ConnectivityManager) getSystem开发者_运维百科Service(Context.CONNECTIVITY_SERVICE);

Otherwise I get a nullpointer-exception straight ahead? How can I fix this? I want my background service to only work, when it is connected to wlan. But that Nullpointerexception just kills the whole app...

Add to the manifest the following line:

<uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />

Yes, I am late but in case someone is still looking,

ConnectivityManager cm = (ConnectivityManager) this.getSystemService(CONNECTIVITY_SERVICE);
NetworkInfo activeNetwork = cm.getActiveNetworkInfo();

no need of Context in the getSystemService() argument.

ConnectivityManager cm = (ConnectivityManager) getSystemService(CONNECTIVITY_SERVICE);
NetworkInfo netInfo = cm.getActiveNetworkInfo();

if (netInfo != null && netInfo.getType() == 1) {
 // CONNECTION_WIFI = true;
}