Fragments toolbar back button not showing

Question

I set my custom toolbar and set "setHomeButtonEnabled" and "setDisplayHomeAsUpEnabled" to true and for some odd reason the toolbar is showing but not the actual back button. I've tried setting a custom icon and setting the toolbar onclick when the fragment is being changed and the toolbar always shows but the backarrow never shows. Is it possibly because my registeractivity is not being called?

public class RegisterActivity extends BaseActivity {


@Override
public void onCreate(Bundle savedInstanceState){
    super.onCreate(savedInstanceState);
    //setContentView(R.layout.activity_register);
    ButterKnife.bind(this);

    Toolbar toolbar = findViewById(R.id.my_toolbar);
    toolbar.setNavigationIcon(R.drawable.abc_ic_ab_back_material);

    setSupportActionBar(toolbar);
    getSupportActionBar().setHomeButtonEnabled(true);
    getSupportActionBar().setDisplayHomeAsUpEnabled(true);
}

the activity where the fragments go

    <?xml version="1.0" encoding="utf-8"?>
    <android.support.design.widget.CoordinatorLayout 
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:background="@color/ghostWhiteColor"
    android:fitsSystemWindows="true"

    tools:context="com.vice.de.flu.activity.RegisterActivity">

    <android.support.design.widget.AppBarLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content">

        <android.support.v7.widget.Toolbar
            android:id="@+id/my_toolbar"
            android:layout_width="match_parent"
            android:layout_height="?attr/actionBarSize"
            android:background="@color/holo_blue_light"/>
    </android.support.design.widget.AppBarLayout>


    <!--wizard>-->
    <FrameLayout
        android:id="@+id/fragment_register"
        android:layout_width="match_parent"
        android:layout_height="match_parent"/>

</android.support.design.widget.CoordinatorLayout>

my manifest

<application
    android:allowBackup="true"
    android:icon="@mipmap/ic_launcher"
    android:label="@string/app_name"
    android:roundIcon="@mipmap/ic_launcher_round"
    android:supportsRtl="true"
    android:theme="@style/AppTheme">
    <activity android:name=".activity.MainActivity">
        <intent-filter>
            <action android:name="android.intent.action.MAIN" />

            <category android:name="android.intent.category.LAUNCHER" />
        </intent-filter>
    </activity>
    <activity android:name=".activity.RegisterActivity"
        android:windowSoftInputMode="adjustPan|adjustResize">

    </activity>
</application>

Answer 1

<android.support.v7.widget.Toolbar
   android:id="@+id/my_toolbar"
   android:layout_width="match_parent"
   android:layout_height="?attr/actionBarSize"
   android:background="@color/holo_blue_light"
   app:navigationIcon="@drawable/back_navigation_icon" />