NavigationView get/find header layout

In my NavigationView I have a header layout with id 'viewId' with active buttons. To setup those buttons, I do the following in activity's onPostCreate:

final View panel = findViewById(R.id.viewId);
panel.setOnClickListener(new View.OnClickListener() {
... setup goes here ...
});

With new version android support library, (23.1.0), the view can't be found, it returns null. With previous versions it worked well. Is it a bug or am I using this feature wrong? If so, how to access header layout and add behavior to it?

Version 23.1.0 switches NavigationView to using a RecyclerView (rather than the previous ListView) and the header is added as one of those elements. This means it is not instantly available to call findViewById() - a layout pass is needed before it is attached to the NavigationView.

For version 23.1.1 of the Support Library, you can now get a reference to the header view using getHeaderView():

View headerLayout = navigationView.getHeaderView(0); // 0-index header

This has the advantage of working on headers added via XML and via code.

If you are still using 23.1.0, as per the related bug, you can inflate the header in code and use findViewById() on that:

View headerLayout = 
    navigationView.inflateHeaderView(R.layout.navigation_header);
panel = headerLayout.findViewById(R.id.viewId);
// panel won't be null

Until you move to 23.1.1.

Now with the 23.1.1 release of the design support library, you can use

NavigationView navigationView = (NavigationView) findViewById(R.id.your_nav_view_id);
View header = navigationView.getHeaderView(0)
TextView text = (TextView) header.findViewById(R.id.textView);

This is how I did it using ButterKnife and it works for me.

protected static class HeaderViewHolder {

    @BindView(R.id.button)
    Button button;

    HeaderViewHolder(View view) {
        ButterKnife.bind(this, view);
    }
}

and then use this view holder like this :

View header = navigationView.getHeaderView(0);
headerViewHolder = new HeaderViewHolder(header);

For me that was the same situation with 23.1.0, after of update the null pointer exception become. In this case the NavigatorView look like:

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

I tried the solution proposal by ianhanniballake but it does not work. Then I inflated with the sentence:

LayoutInflater.from(getContext()).inflate(R.layout.nav_header, mNavigationView);

After that, I can find by id all views defined in nav_heardlayout .

NavigationView navigationView = findViewById(R.id.your_nav_view);
View header = navigationView.getHeaderView(0);
TextView textUsername = header.findViewById(R.id.textView);
textUsername.setText("you text here ");

NavigationView navigationView = findViewById(R.id.your_nav_view);
View header = navigationView.getHeaderView(0);
TextView textUsername = header.findViewById(R.id.textView);
textUsername.setText("you text here ")

In Kotlin @Francois Dermu code be like

val navigationView : NavigationView = findViewById(R.id.your_nav_view_id);
val header = navigationView.getHeaderView(0)
val textView = header.findViewById<TextView>(R.id.textView)

Kotlin version.

val navView: NavigationView = findViewById(R.id.nav_view)       
// set User Name
val headerView: View = navView.getHeaderView(0)
headerView.txtUserName.text = "User Name Goes here"