java - com.google.zxing.client.android.result return a Null pointer exception -

i trying develop simple app read qr code zxing , redirect corresponding link. mainactivity class, methods on create , onactivityresult, when scan qr code app crashes....and dunno why can me? post mainactivity class, if can help...

thanks all

fabrizio

-------- mainactivity------------

public class mainactivity extends activity {  // static final string action_scan = "com.google.zxing.client.android.scan"; private button button; private webview webview; @override protected void oncreate(bundle savedinstancestate) {      final context context = this;     super.oncreate(savedinstancestate);     setcontentview(r.layout.activity_main);     button = (button) findviewbyid(r.id.go_direct);      button.setonclicklistener(new onclicklistener() {          @override         public void onclick(view arg0) {             intent intent = new intent(context, webviewactivity.class);             startactivity(intent);         }      });  }  public void scannow(view view) {      intent intent = new intent("com.google.zxing.client.android.scan");     // intent.setpackage("com.google.zxing.client.android");     intent.putextra("com.google.zxing.client.android.scan.scan_mode",             "qr_code_mode");     startactivityforresult(intent, 0);  }  @suppresslint("setjavascriptenabled")  public void onactivityresult(int requestcode, int resultcode, intent intent) {     if (requestcode == 0) {         if (resultcode == result_ok) {             string contents = intent.getstringextra("scan_result");              log.i("intent", intent.tostring());             log.i("scan result", intent.getstringextra("scan_result"));              string format = intent.getstringextra("scan_result_format");             log.i("xzing", "contents: " + contents + " format: " + format); // handle                                                                 // successful                                                                             // scan             setcontentview( r.layout.web_view);             webview = (webview) findviewbyid(r.id.webview1);             webview.getsettings().setjavascriptenabled(true);             webview.setwebviewclient(new mywebviewclient());             webview.loadurl(contents);         } else if (resultcode == result_canceled) { // handle cancel             log.i("xzing", "cancelled");         }     } }  @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);}}