Instance of header view of navigation view in Android is always null

Question

I am developing an Android app. In my app, I am working with navigation view. I need to change design of header view programmatically according to a situation. But variable of the instance of header view is always throwing null exception. What is wrong with my code?

This is how I set header view in navigation view

<android.support.design.widget.NavigationView
        app:itemIconTint="@drawable/drawer_item"
        app:itemTextColor="@drawable/drawer_item"
        android:id="@+id/left_nv_view"
        app:headerLayout="@layout/header_view"
        android:layout_width="wrap_content"
        android:layout_height="match_parent"
        android:layout_gravity="start" />

This is the layout of my header view

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/header_view"
    android:orientation="vertical" android:layout_width="match_parent"
    android:layout_height="wrap_content">

</LinearLayout>

This is how I instantiate header view and make changes to it in activity

  //I initialized navigation drawer and navigation view first 
   headerView = (LinearLayout)findViewById(R.id.header_view);
   headerView.setOrientation(LinearLayout.VERTICAL);

But it always throwing null pointer exception. How can I fix my code?

Answer 1

A NavigationView takes some time to get its header Views inflated and laid out. Often, this will not be complete until after onCreate() has finished, but you can force it to happen immediately by using the NavigationView#getHeaderView() method.

After the headers have been successfully loaded, you would then be able to find them in the Activity's View hierarchy, and your call to findViewById() wouldn't return null.