How to access layout elements of one activity file in another activity file in android -

i have 3 tabs (like whatsapp) , load same webview(which defined in activity_main.xml) in bottom want load relative layout in tab2(which defined in android_fragment.xml). unfortunately when access element using findviewbyid showing nothing not error message.

so confused. possible call layout elements of activity file in activity file using findviewbyid or there other way ?

     mainactivity.java      public void ontabselected(tab tab, fragmenttransaction ft) {      mainfragment mainfragment=      (mainfragment)getfragmentmanager().findfragmentbyid(r.id.content_frame);     if(mainfragment==null){         log.d("main frame null", "returning ");         return;     }     string value = tab.gettext().tostring();     log.d("tab value", value);     if (value.equalsignorecase("tab1")) {         mainfragment.executejavascriptfunction("tab1()");         //webview.loadurl("javascript:tab1();");      } else if (value.equalsignorecase("tab2")) {         system.out.println("inside tab2");         imagebutton.setvisibility(0);         edittext.setvisibility(0);         /*txtview.setvisibility(0);*/     /*mainfragment.executejavascriptfunction("tab2()");         {          edit=  (edittext)findviewbyid(r.id.edittext1);         log.d("value of editext", edit.tostring());     edit.setvisibility(0);         }          //webview.loadurl("javascript:tab2();");         */     } else if (value.equalsignorecase("tab3")) {         mainfragment.executejavascriptfunction("tab3()");         //webview.loadurl("javascript:tab3();");         imagebutton.setvisibility(view.gone);         edittext.setvisibility(view.gone);      }