TextView from Navigation Header is null

Question

I'm trying to implement a navigation drawer with NavigationView. Everthing works fine so far, every item is displayed correctly. However there is a NullPointerException in this lines :

View header = navigationView.getHeaderView(0);
TextView username = (TextView) header.findViewById(R.id.profile_name_id);
username.setText(mUser.getUsername());

In this line username.setText(mUser.getUsername()); the NullPointerExption is thrown. The strange thing is that it still displays the correct text of mUser.getUsername() This is the NavigationView:

<android.support.design.widget.NavigationView
        android:id="@+id/navigation_view"
        android:layout_height="match_parent"
        android:layout_width="wrap_content"
        android:layout_gravity="start"
        app:headerLayout="@layout/drawer_header"
        app:menu="@menu/drawer"/>

Drawer_header:

 <?xml version="1.0" encoding="utf-8"?>
<LinearLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:paddingTop="20dp"
    android:paddingBottom="20dp"
    android:background="@color/primary_dark"
    android:layout_width="match_parent"
    android:layout_height="160dp">

    <ImageView
        android:id="@+id/profile_pic_id"
        android:src="@drawable/account_big"
        android:layout_width="wrap_content"
        android:layout_gravity="center"
        android:layout_weight="1"
        android:layout_height="0dp"/>
    <android.widget.TextView
        android:id="@+id/profile_name_id"
        android:textColor="@color/primary_text"
        android:textSize="18sp"
        android:layout_gravity="center"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content" />
</LinearLayout>

Drawer:

<?xml version="1.0" encoding="utf-8"?>
<menu xmlns:android="http://schemas.android.com/apk/res/android">

    <group android:checkableBehavior="single">

        <item
            android:id="@+id/home_id"
            android:checked="false"
            android:icon="@drawable/home"
            android:title="@string/home" />

        <item
            android:id="@+id/create_set_id"
            android:checked="false"
            android:icon="@drawable/add_box"
            android:title="@string/create_learnset" />

        <item
            android:id="@+id/logout_id"
            android:checked="false"
            android:icon="@drawable/logout"
            android:title="@string/logout" />
    </group>
</menu>

Answer 1

You need to only write Text View.

Change this

<android.widget.TextView
        android:id="@+id/profile_name_id"
        android:textColor="@color/primary_text"
        android:textSize="18sp"
        android:layout_gravity="center"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content" />

To this.

  <TextView
        android:id="@+id/profile_name_id"
        android:textColor="@color/primary_text"
        android:textSize="18sp"
        android:layout_gravity="center"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content" />

It's Done.