android - how to find id of layout in a Bitmap Button java source that I made -

i made bitmap button has animation effect on layout cannot find id of layout , says indicates null point

here source below

public class bitmapbutton extends button{  public bitmapbutton(context context) {     super(context);     init(); }  public bitmapbutton(context context, attributeset attrs) {     super(context, attrs);     init(); }  private void init(){    setbackgroundresource(r.drawable.background_selector);      setonclicklistener(new onclicklistener() {         boolean selected=true;         animation anim;          linearlayout layout_search = (linearlayout)findviewbyid(r.id.layout_search);          @override         public void onclick(view v) {              if(selected) {                 setselected(true);                 anim = animationutils.loadanimation(getcontext(), r.anim.translate_down);                 ***layout_search.startanimation(anim);***                 layout_search.setvisibility(view.visible);                 selected =!selected;             }             else{                 setselected(false);                 anim = animationutils.loadanimation(getcontext(), r.anim.translate_up);                 layout_search.startanimation(anim);                 layout_search.setvisibility(view.gone);                 selected =!selected;             }         }     }); } } 

========================================================================= layout_search.startanimation(anim);

from here gets wrong saying

java.lang.nullpointerexception: attempt invoke virtual method void android.widget.linearlayout.startanimation(android.view.animation.animation) on null object reference

i know findviewbyid method in button class different 1 in mainactivity dont know then, how can find linearlayout linear_search?? problem can make anim effection on button. plz let me know...

    public class bitmapbutton extends button{      public bitmapbutton(context context) {         super(context);         init();     }      public bitmapbutton(context context, attributeset attrs) {         super(context, attrs);         init();     }      private void init(){        setbackgroundresource(r.drawable.background_selector);          setonclicklistener(new onclicklistener() {             boolean selected=true;             animation anim;            // _____________ commented out line ______________    //  linearlayout layout_search = (linearlayout)v.findviewbyid(r.id.layout_search);             @override             public void onclick(view v) {      // add line here , add view v before findviewbyid      linearlayout layout_search = (linearlayout)v.findviewbyid(r.id.layout_search);                   if(selected) {                     setselected(true);                     anim = animationutils.loadanimation(getcontext(), r.anim.translate_down);                     ***layout_search.startanimation(anim);***                     layout_search.setvisibility(view.visible);                     selected =!selected;                 }                 else{                     setselected(false);                     anim = animationutils.loadanimation(getcontext(), r.anim.translate_up);                     layout_search.startanimation(anim);                     layout_search.setvisibility(view.gone);                     selected =!selected;                 }             }         });     }     }