android crash when using setVisibility(View.VISIBLE) -

i seem getting application crashes at:

parent.findviewbyid(r.id.a_1).setvisibility(view.visible);

not sure im doing wrong

code below

layouttext.java

    public class layouttest extends activity {  private spinner solvefor;   private arrayadapter<charsequence> featuresadapter;   private list<charsequence> featureslist;       /** called when activity first created. */     @override     public void oncreate(bundle savedinstancestate) {         super.oncreate(savedinstancestate);         setcontentview(r.layout.main);         featureslist = new arraylist<charsequence>();          featuresadapter = new arrayadapter<charsequence>(this, android.r.layout.simple_spinner_item, featureslist);          featuresadapter.setdropdownviewresource(android.r.layout.simple_spinner_dropdown_item);          solvefor = ((spinner) layouttest.this.findviewbyid(r.id.solvefor));          solvefor.setadapter(featuresadapter);          featuresadapter.add("velocity");          featuresadapter.add("time");          featuresadapter.add("distance");          solvefor.setonitemselectedlistener(new myonitemselectedlistener());     } } 

myonitemselectedlistener.java package android.example.layouttest;

import android.view.view; import android.widget.adapterview; import android.widget.adapterview.onitemselectedlistener; import android.widget.toast;  public class myonitemselectedlistener implements onitemselectedlistener {  private static final int spinner_option_first = 0;      private static final int spinner_option_second = 1;  public void onitemselected(adapterview<?> parent, view view, int pos, long id) {    switch(pos) {           case spinner_option_first: {            toast.maketext(parent.getcontext(), "0", toast.length_long).show();           break;          }           case spinner_option_second: {            toast.maketext(parent.getcontext(), "1", toast.length_long).show();           parent.findviewbyid(r.id.a_1).setvisibility(view.visible);           parent.findviewbyid(r.id.a_2).setvisibility(view.visible);           break;          }    }    }     public void onnothingselected(adapterview<?> parent) {          // nothing.        } } 

remember view#findviewbyid starts search view call on , descends children. if view id you're looking not either view or descendant of view, search fail , findviewbyid return null.

as falmarri suggests, may not want call findviewbyid on parent in context. (you might not want call on view there either.)

where in view hierarchy expecting find r.id.a_1?