android - NullPointer Exception in getWidth(), getHeight() -

i working on project . need width & height of linearlayout activity using programming code. linear layout has fixed width , height . when use following ..i getting nullpointer exception

linearlayout viewgroup = (linearlayout) context.findviewbyid(r.id.popup); log.e("getwidth",""+viewgroup.getwidth()); log.e("getheight",""+viewgroup.getheight()); 

i need width , height of layout activity.

<linearlayout xmlns:android="http://schemas.android.com/apk/res/android" android:id="@+id/popup" android:layout_width="150dp" android:layout_height="252dp" android:background="#303030" android:orientation="vertical" > </linearlayout> 

here java code file

public class mainactivity extends activity {

//the "x" , "y" position of "show button" on screen. point p; button btn_show;  @override public void oncreate(bundle savedinstancestate) {    super.oncreate(savedinstancestate);    setcontentview(r.layout.activity_main);    btn_show = (button) findviewbyid(r.id.show_popup);  }    @override protected void onresume() {     super.onresume();      btn_show.setonclicklistener(new onclicklistener() {          @override          public void onclick(view arg0) {             //open popup window            if (p != null)            showpopup( p);          }        }); }    // x , y position after button draw on screen // (it's important note can't position in oncreate(), // because @ stage view isn't drawn yet, return (0, 0)) @override public void onwindowfocuschanged(boolean hasfocus) {     int[] location = new int[2];    button button = (button) findviewbyid(r.id.show_popup);     // x, y location , store in location[] array    // location[0] = x, location[1] = y.    button.getlocationonscreen(location);     //initialize point x, , y positions    p = new point();    p.x = location[0];    p.y = location[1]; }  // method displays popup. private void showpopup( point p) {    int popupwidth = 200;    int popupheight = 380;     // inflate popup_layout.xml    linearlayout viewgroup = (linearlayout) findviewbyid(r.id.popup);    layoutinflater layoutinflater = (layoutinflater) getsystemservice(context.layout_inflater_service);    view layout = layoutinflater.inflate(r.layout.a, viewgroup);    log.e("getwidth",""+viewgroup.getwidth());    log.e("getheight",""+viewgroup.getheight());     // creating popupwindow    final popupwindow popup = new popupwindow(getapplicationcontext());    popup.setcontentview(layout);    popup.setwidth(viewgroup.getwidth());    popup.setheight(viewgroup.getheight());    popup.setfocusable(true);     // offset align popup bit right, , bit down, relative button's position.    int offset_x = 30;    int offset_y = 30;     // clear default translucent background    popup.setbackgrounddrawable(new bitmapdrawable());     // displaying popup @ specified location, + offsets.    popup.showatlocation(layout, gravity.no_gravity, p.x + offset_x, p.y + offset_y);     // getting reference close button, , close popup when clicked.   // button close = (button) layout.findviewbyid(r.id.close);   /* close.setonclicklistener(new onclicklistener() {       @override      public void onclick(view v) {        popup.dismiss();      }    });*/ } } 

it may viewgroup hasn't been created yet.

check you're trying width , height of object being called after display objects such views etc being created. can debug either placing breakpoints in different loading methods such oncreate, onresume or placing nslog's in them instead.