android - Null Pointer Exception on drawer Layout -

i getting null pointer exception @ drawerlayout=(drawerlayout) findviewbyid(r.layout.drawer_layout);

please me out. why returning null pointer exception? don't know doing wrong.

package com.example.prototype;  import android.app.actionbar; import android.app.activity; import android.os.bundle; import android.support.v4.app.actionbardrawertoggle; import android.support.v4.widget.drawerlayout; import android.support.v4.widget.drawerlayout.drawerlistener; import android.view.menu; import android.view.menuitem; import android.view.view; import android.widget.arrayadapter; import android.widget.listview; import android.widget.toast;  public class mainactivity extends activity  {      drawerlayout drawerlayout;           actionbar action_bar;     listview navigation_list;     actionbardrawertoggle drawertoggle;     string items[];      protected void oncreate(bundle savedinstancestate) {         super.oncreate(savedinstancestate);         setcontentview(r.layout.drawer_layout);         initcomponents();         action_bar=getactionbar();         setnavigationlist();     }      @suppresswarnings("deprecation")     private void setnavigationlist() {          int open=r.string.navigation_open;         int close=r.string.navigation_close;         navigation_list.setadapter(new arrayadapter<string>(this, android.r.layout.simple_list_item_1, items));          drawertoggle=new actionbardrawertoggle(this,drawerlayout, r.drawable.ic_menu_white_18dp,open,close){               public void ondrawerclosed(view view) {                  super.ondrawerclosed(view);                  action_bar.show();              }               public void ondraweropened(view drawerview) {                  super.ondraweropened(drawerview);                  action_bar.hide();              }         };          if(drawerlayout==null){             toast.maketext(getapplicationcontext(), "null", toast.length_long).show();         } else {             drawerlayout.setdrawerlistener(drawertoggle);             action_bar.setdisplayhomeasupenabled(true);             action_bar.sethomebuttonenabled(true);         }         }      private void initcomponents() {          // todo auto-generated method stub           drawerlayout=(drawerlayout) findviewbyid(r.layout.drawer_layout);          action_bar=getactionbar();          navigation_list=(listview) findviewbyid(r.id.left_drawer);          items=getresources().getstringarray(r.array.navigation_drawer);           if(drawerlayout==null){             toast.maketext(getapplicationcontext(), "null0", toast.length_long).show();         }     }      @override     public boolean oncreateoptionsmenu(menu menu) {         // inflate menu; adds items action bar if present.         getmenuinflater().inflate(r.menu.main, menu);         return true;     }      @override     public boolean onoptionsitemselected(menuitem item) {         // handle action bar item clicks here. action bar         // automatically handle clicks on home/up button, long         // specify parent activity in androidmanifest.xml.         int id = item.getitemid();         if (id == r.id.action_settings) {             return true;         }          if (id == r.id.search_menu) {             toast.maketext(getapplicationcontext(), "searched clicked ", toast.length_long).show();             return true;         }          if (id == r.id.share_menu) {             toast.maketext(getapplicationcontext(), "share clicked ", toast.length_long).show();             return true;         }          if (id == r.id.navigation_menu) {             toast.maketext(getapplicationcontext(), "navigation clicked ", toast.length_long).show();             return true;         }         return super.onoptionsitemselected(item);     } } 

here xml file

<?xml version="1.0" encoding="utf-8"?> <android.support.v4.widget.drawerlayout       xmlns:android="http://schemas.android.com/apk/res/android"     android:id="@+id/drawer_layout"     android:layout_width="match_parent"     android:layout_height="match_parent">      <framelayout          android:id="@+id/content_frame"         android:layout_width="match_parent"         android:layout_height="match_parent" />           <listview android:id="@+id/left_drawer"         android:layout_width="240dp"         android:layout_height="match_parent"         android:layout_gravity="start"         android:choicemode="singlechoice"         android:divider="@android:color/transparent"         android:dividerheight="5dp"         android:background="#e1e1e1"/> </android.support.v4.widget.drawerlayout> 

it has

         drawerlayout=(drawerlayout) findviewbyid(r.id.drawer_layout); 

so r.id instad of r.layout because referring element, not xml file.