Android, findViewById returns null -

i'm writing code android, matter that, when call findviewbyid returns me null, , cannot understand why! i've been wasting brain since yesterday, cannot figure out solution. goal set layout header listview. here code, respectively header , page:

<?xml version="1.0" encoding="utf-8"?> <linearlayout xmlns:android="http://schemas.android.com/apk/res/android"     android:id="@+id/header"     android:orientation="horizontal"     android:layout_width="match_parent"     android:layout_height="wrap_content"     android:layout_marginbottom="5dp">      <textview         android:text="@string/bydistance"         android:layout_gravity="left"         android:layout_width="0dp"         android:layout_weight="1"         android:layout_height="wrap_content"         android:textsize="13dp"         android:gravity="center_horizontal"/>      <textview         android:text="@string/byactivity"         android:layout_gravity="right"         android:layout_width="0dp"         android:layout_weight="1"         android:layout_height="wrap_content"         android:textsize="13dp"         android:gravity="center_horizontal"/>  </linearlayout>  <?xml version="1.0" encoding="utf-8"?> <linearlayout xmlns:android="http://schemas.android.com/apk/res/android"           android:orientation="vertical"           android:layout_width="match_parent"           android:layout_height="match_parent"           android:background="#ff0000"     >      <listview         android:id="@+id/parklist"         android:layout_height="wrap_content"         android:layout_width="match_parent"         android:divider="@android:color/transparent"         android:dividerheight="5.0dp">     </listview>  </linearlayout> 

and here code call addheaderview:

public class nearmefragment extends fragment implements view.onclicklistener{  private fragmentmanager fragmentmanager;  @override public void oncreate(bundle savedbundle){     super.oncreate(savedbundle); }  @override public view oncreateview (layoutinflater inflater, viewgroup container, bundle savedbundle) {     view v = inflater.inflate(r.layout.park_list, container, false);      //todo remove     make_test(v, container);      return v; }  public void opentest(view view){     new livecomment().show(getchildfragmentmanager(), "dialog"); }  public void onclick(view view){     if (fragmentmanager == null)         fragmentmanager = getchildfragmentmanager();     //if (view.getid() == r.id.test){         fragmentmanager.begintransaction().add(new livecomment(), "livecomment").commit(); }  private void make_test(view v, viewgroup container) {      listview listview = (listview) v.findviewbyid(r.id.parklist);     park[] list = new park[3];     list[0] = new park("parco a", "acquasparta", false, false, 1, 2, 3);     list[1]=new park("parco b", "perugia", false, false, 1, 2, 3);     list[2]=new park("parco b", "perugia", false, false, 1, 2, 3);     parklistadapter adapter = new parklistadapter(v.getcontext(), r.layout.small_park_container,list);     linearlayout header = (linearlayout) container.findviewbyid(r.id.header);     listview.addheaderview(header);     listview.setadapter(adapter);  } } 

the error given @

listview.addheaderview(header) 

r.id.header inside v not inside container.

change

linearlayout header = (linearlayout) container.findviewbyid(r.id.header); 

with

linearlayout header = (linearlayout) v.findviewbyid(r.id.header); 

about viewgroup container doc says:

if non-null, parent view fragment's ui should attached to. fragment should not add view itself, can used generate layoutparams of view.

edit: since header view in layout have inflate too:

@override public view oncreateview (layoutinflater inflater, viewgroup container, bundle savedbundle) {     view v = inflater.inflate(r.layout.park_list, container, false);     view header = inflater.inflate(r.layout.headerlayout, null);     //todo remove     make_test(v, header);      return v; } 

and

private void make_test(view v, view header) {       // code        //  have remove linearlayout header = (linearlayout) container.findviewbyid(r.id.header);     listview.addheaderview(header);     listview.setadapter(adapter);  }