Warum mein Menüsymbol nicht in der Symbolleiste angezeigt wird, zeige nur leere Symbolleiste

Question

Ich versuche, Symbolmenü in der Symbolleiste hinzuzufügen. aber mein Icon wird nicht angezeigt. hier mein Code. Nur leere Kopfzeile anzeigen. kann mir jemand helfen ...

dieses Fragment Klasse

package com.example.bams.task.fragments; 

import android.app.ActionBar; 
import android.app.Fragment; 
import android.content.Context; 
import android.os.Bundle; 
import android.support.annotation.Nullable; 
import android.support.v4.app.FragmentManager; 
import android.support.v7.app.AppCompatActivity; 
import android.support.v7.widget.Toolbar; 
import android.view.LayoutInflater; 
import android.view.Menu; 
import android.view.MenuInflater; 
import android.view.MenuItem; 
import android.view.View; 
import android.view.ViewGroup; 
import android.widget.Toast; 

import com.example.bams.task.R; 

/** 
* Created by jack on 19/02/2017. 
*/ 

public class AddProjectFragment extends Fragment { 
    @Override 
    public void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 
     setHasOptionsMenu(true); 

     Toolbar myToolbar = (Toolbar) getActivity().findViewById(R.id.my_toolbar); 
     ((AppCompatActivity) getActivity()).setSupportActionBar(myToolbar); 
    } 

    @Nullable 
    @Override 
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) { 
     View rootView = inflater.inflate(R.layout.fragment_add_project, container,false); 
     return rootView; 
    } 

    @Override 
    public void onCreateOptionsMenu(Menu menu, MenuInflater inflater) { 
     //menu.clear(); 
     inflater.inflate(R.menu.header, menu); 
     super.onCreateOptionsMenu(menu, inflater); 
    } 
} 

dieses Layout meine benutzerdefinierte Symbolleiste

<?xml version="1.0" encoding="utf-8"?> 
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" 
    android:orientation="vertical" android:layout_width="fill_parent" 
    android:layout_height="fill_parent" 
    android:background="@color/colorBgFragment" 
    android:fitsSystemWindows="true" 
    xmlns:app="http://schemas.android.com/apk/res-auto"> 

    <android.support.v7.widget.Toolbar 
     android:id="@+id/my_toolbar" 
     android:layout_width="match_parent" 
     android:layout_height="?attr/actionBarSize" 
     android:background="?attr/colorPrimary" 
     android:elevation="4dp" 
     android:theme="@style/ThemeOverlay.AppCompat.ActionBar" 
     app:popupTheme="@style/ThemeOverlay.AppCompat.Light"/> 

    <LinearLayout 
     android:layout_width="match_parent" 
     android:layout_height="match_parent" 
     android:background="@color/colorBgFragment"> 
     <EditText 
      android:layout_width="match_parent" 
      android:layout_height="wrap_content" 
      android:inputType="textPersonName" 
      android:text="Name" 
      android:ems="10" 
      android:id="@+id/editText"/> 
    </LinearLayout> 

</LinearLayout> 

und mein Menüsymbol jemand

<?xml version="1.0" encoding="utf-8"?> 
<menu xmlns:android="http://schemas.android.com/apk/res/android" 
    xmlns:app="http://schemas.android.com/apk/res-auto"> 
    <item 
     android:id="@+id/backBtn" 
     android:icon="@drawable/ic_back_filled" 
     app:showAsAction="always" 
     android:title="back"/> 
</menu> 

kann sagen, ist mir

was falsch mit meinem Code?