android - Null Pointer error when trying to utilize a class with AlertDialog.Builder -

trying inflate alertdialog.builder. i'm trying date wheel (yuri kanivets' wheel) appear inside of dialog. since exact code need exists inside 1 of classes, i'm trying instantiate new instance of dateactivity class (which i've imported project), , add dialog. unfortunately, can't seem connect dateactivity object dialog. thought 1 of arguments inflate view, crashes. here's code:

edit: clarify, in code follows there no errors. problem mentioned there no usage, , therefore no connection, of dateactivity variable alertdialog.builder. i've tried using variable (datewheelselector) argument builderview , builder variable instantiations, both of these crash. need figure out how connect these since right dialog empty.

private void setstartdate() {      //somehow need use variable, where???     dateactivity datewheelselector = new dateactivity();      layoutinflater inflater = layoutinflater.from(this);      view builderview = inflater.inflate(r.layout.wheel_date_layout, null);     alertdialog.builder builder = new alertdialog.builder(this);     builder.setview(builderview);            alert = builder.create();      /* set title of dialog programatically */     textview title = (textview) builderview.findviewbyid(r.id.date_title);     title.settext("choose start date");      alert.show(); } 

thanks suggestions.

you cannot add activity dialog. can either define activity dialog (see android activity dialog) or can refactor dateactivity dialogfragment (see http://developer.android.com/reference/android/app/dialogfragment.html) can used fragment or dialog.