java - How to change layout background dynamically -

i having problem in code.i trying change layout background of app every second.i used thread in code.i've searched site couldn't find useful.here code.

import android.app.activity; import android.graphics.bitmap; import android.graphics.bitmapfactory; import android.os.bundle; import android.view.motionevent; import android.view.view; import android.view.view.ontouchlistener; import android.widget.linearlayout;  public class mainactivity extends activity {      //private bitmap open, close;     private linearlayout myl;       @override     protected void oncreate(bundle savedinstancestate) {         super.oncreate(savedinstancestate);         setcontentview(r.layout.activity_main);          myl = (linearlayout) findviewbyid(r.id.linearlayout2);          // myl=(linearlayout) findviewbyid(r.id.linearlayout2);          //close = bitmapfactory.decoderesource(getresources(), r.drawable.kapa);         //open = bitmapfactory.decoderesource(getresources(), r.drawable.ac);      }      @override     protected void onresume() {         // todo auto-generated method stub         super.onresume();          thread th = new thread() {             public void run() {                  while (true) {                     myl.setbackgroundresource(r.drawable.kapa);                      try {                         sleep(1000);                     } catch (interruptedexception e) {                         // todo auto-generated catch block                         e.printstacktrace();                     }                      myl.setbackgroundresource(r.drawable.ac);                      try {                         sleep(1000);                     } catch (interruptedexception e) {                         // todo auto-generated catch block                         e.printstacktrace();                     }                  }             }         };         th.start();     }  } 

try this:

public class mainactivity extends activity {  //private bitmap open, close; private linearlayout myl;   @override protected void oncreate(bundle savedinstancestate) {     super.oncreate(savedinstancestate);     setcontentview(r.layout.activity_main);      myl = (linearlayout) findviewbyid(r.id.linearlayout2);      // myl=(linearlayout) findviewbyid(r.id.linearlayout2);      //close = bitmapfactory.decoderesource(getresources(), r.drawable.kapa);     //open = bitmapfactory.decoderesource(getresources(), r.drawable.ac);  }  @override protected void onresume() {     // todo auto-generated method stub     super.onresume();      runnable runnable = new runnable() {           @override           public void run() {                while(true) {               try {                   thread.sleep(1000);                 } catch (interruptedexception e) {                   e.printstacktrace();                 }                mainactivity.this.runonuithread(new runnable() {                 @override                 public void run() {                     myl.setbackgroundresource(r.drawable.kapa);                  }             });               try {                   thread.sleep(1000);                 } catch (interruptedexception e) {                   e.printstacktrace();                 }                mainactivity.this.runonuithread(new runnable() {                     @override                     public void run() {                         myl.setbackgroundresource(r.drawable.ac);                      }                 });             }           }         };         new thread(runnable).start(); }  }