wifi - Android WifiManeger Class startCustomizedScan(ScanSettings requested) function application force stop -

i must use startcustomizedscan(scansettings requested) function. request scan access points in specified channel list. each channel specified frequency in mhz, e.g. "2437"

 wifichannel mrtchannel;  mrtchannel = new wifichannel();   mrtchannel.freqmhz = 2437;  mrtchannel.channelnum = 6;   scansettings set ;  mrtcollection = null;   mrtcollection.add(mrtchannel);   set = (scansettings)mrtcollection;  mainwifi.startcustomizedscan(set); 

but application force stop. application not laucnh. logcat

08-30 23:09:36.547: e/androidruntime(14327): fatal exception: main 08-30 23:09:36.547: e/androidruntime(14327): process: com.muratucan.murat5hidden, pid: 14327 08-30 23:09:36.547: e/androidruntime(14327): java.lang.runtimeexception: unable start activity componentinfo{com.muratucan.murat5hidden/com.muratucan.murat5hidden.mainactivity}: java.lang.nullpointerexception: attempt invoke interface method 'boolean java.util.collection.add(java.lang.object)' on null object reference 08-30 23:09:36.547: e/androidruntime(14327):    @ android.app.activitythread.performlaunchactivity(activitythread.java:2305) 08-30 23:09:36.547: e/androidruntime(14327):    @ android.app.activitythread.handlelaunchactivity(activitythread.java:2367) 08-30 23:09:36.547: e/androidruntime(14327):    @ android.app.activitythread.access$800(activitythread.java:148) 08-30 23:09:36.547: e/androidruntime(14327):    @ android.app.activitythread$h.handlemessage(activitythread.java:1283) 08-30 23:09:36.547: e/androidruntime(14327):    @ android.os.handler.dispatchmessage(handler.java:102) 08-30 23:09:36.547: e/androidruntime(14327):    @ android.os.looper.loop(looper.java:135) 08-30 23:09:36.547: e/androidruntime(14327):    @ android.app.activitythread.main(activitythread.java:5274) 08-30 23:09:36.547: e/androidruntime(14327):    @ java.lang.reflect.method.invoke(native method) 08-30 23:09:36.547: e/androidruntime(14327):    @ java.lang.reflect.method.invoke(method.java:372) 08-30 23:09:36.547: e/androidruntime(14327):    @ com.android.internal.os.zygoteinit$methodandargscaller.run(zygoteinit.java:909) 08-30 23:09:36.547: e/androidruntime(14327):    @ com.android.internal.os.zygoteinit.main(zygoteinit.java:704) 08-30 23:09:36.547: e/androidruntime(14327): caused by: java.lang.nullpointerexception: attempt invoke interface method 'boolean java.util.collection.add(java.lang.object)' on null object reference 08-30 23:09:36.547: e/androidruntime(14327):    @ com.muratucan.murat5hidden.mainactivity.oncreate(mainactivity.java:133) 08-30 23:09:36.547: e/androidruntime(14327):    @ android.app.activity.performcreate(activity.java:5977) 08-30 23:09:36.547: e/androidruntime(14327):    @ android.app.instrumentation.callactivityoncreate(instrumentation.java:1105) 08-30 23:09:36.547: e/androidruntime(14327):    @ android.app.activitythread.performlaunchactivity(activitythread.java:2258) 

please give me insight in project or other method.

thanks!

my full code here..

public class mainactivity extends activity {  //  wifimanager mainwifi;      public  collection<wifichannel> channelsetcollect;     public collection<wifichannel> mrtcollection = null;     textview ekran ;      textview maintext;     wifimanager mainwifi;     wifireceiver receiverwifi;     list<scanresult> wifilist;     stringbuilder sb = new stringbuilder();        @override     protected void oncreate(bundle savedinstancestate) {         super.oncreate(savedinstancestate);         setcontentview(r.layout.activity_main);           maintext = (textview) findviewbyid(r.id.textview1);          // initiate wifi service manager         mainwifi = (wifimanager) getsystemservice(context.wifi_service);       wifichannel mrtchannel;      mrtchannel = new wifichannel();       mrtchannel.freqmhz = 2437;      mrtchannel.channelnum = 6;       scansettings set ;      mrtcollection = null;       mrtcollection.add(mrtchannel);       set = (scansettings)mrtcollection;      mainwifi.startcustomizedscan(set);           // check wifi disabled         if (mainwifi.iswifienabled() == false)              {                     // if wifi disabled enable                  toast.maketext(getapplicationcontext(), "wifi disabled..making enabled",                   toast.length_long).show();                   mainwifi.setwifienabled(true);              }           // wifi scaned value broadcast receiver          receiverwifi = new wifireceiver();          // register broadcast receiver          // broacast receiver automatically call when number of wifi connections changed         registerreceiver(receiverwifi, new intentfilter(wifimanager.scan_results_available_action));        // mainwifi.startscan();         maintext.settext("starting scan...");      }        @override     public boolean oncreateoptionsmenu(menu menu) {         // inflate menu; adds items action bar if present.         getmenuinflater().inflate(r.menu.main, menu);         return true;     }      @override     public boolean onoptionsitemselected(menuitem item) {         // handle action bar item clicks here. action bar         // automatically handle clicks on home/up button, long         // specify parent activity in androidmanifest.xml.         int id = item.getitemid();         if (id == r.id.action_settings) {             return true;         }         return super.onoptionsitemselected(item);     }      protected void onpause() {         unregisterreceiver(receiverwifi);         super.onpause();     }      protected void onresume() {         registerreceiver(receiverwifi, new intentfilter(wifimanager.scan_results_available_action));         super.onresume();     }      // broadcast receiver class called receive method      // when number of wifi connections changed      class wifireceiver extends broadcastreceiver {          // method call when number of wifi connections changed         public void onreceive(context c, intent intent) {              sb = new stringbuilder();             wifilist = mainwifi.getscanresults();              sb.append("\n        number of wifi connections :"+wifilist.size()+"\n\n");              for(int = 0; < wifilist.size(); i++){                  sb.append(new integer(i+1).tostring() + ". ");                 sb.append((wifilist.get(i)).tostring());                 sb.append("\n\n");             }              maintext.settext(sb);           }     }  } 

you getting nullpointerexception because trying add collection, collection null.

 mrtcollection = null;   mrtcollection.add(mrtchannel); 

what need initialize collection:

 mrtcollection = new arraylist<wifichannel>();  mrtcollection.add(mrtchannel); 

note, can use class implements collection, not arraylist (see collection see classes implement collection). also, can initialize mrtcollection when define variable, or can assign in oncreate.

update: classcastexception, shouldn't casting arraylist scansettings, should creating own scansettings using hidden constructor , setting collection channelset desired channels.