title: Where to findViewById in a Drawer MainActivity?
body: <p>I'm using the Android Studio template for the Drawer Navigation. I wanted to add a click event to the drawer's header, but when I try to findViewById in the onCreate() method, I get a null exception. I'm guessing it's because it hasn't been inflated yet.</p>
  
  <p>Interesting to me is that findViewById on the <strong>drawer_layout</strong> and the <strong>nav_view</strong> returned an object. I tried to do this:</p>
  
  <pre><code>drawer.findViewById;
  </code></pre>
  
  <p>and this:</p>
  
  <pre><code>navigationView.findViewById;
  </code></pre>
  
  <p>But that still gives me an exception.</p>
  
  <p>So my question is two fold:</p>
  
  <ol>
  <li>Why is it that <strong>findViewById</strong> on <strong>drawer_layout</strong> and <strong>nav_view</strong> returned an object while findViewById on <strong>iv_profile</strong> did not?</li>
  <li>Where and how do I avoid the NullPointerException in this case?</li>
  </ol>
  
  <p><strong>MainActivity.java</strong></p>
  
  <pre><code>public class MainActivity extends AppCompatActivity
          implements NavigationView.OnNavigationItemSelectedListener {
  
      @Override
      protected void onCreate(Bundle savedInstanceState) {
          super.onCreate(savedInstanceState);
          setContentView(R.layout.activity_main);
          Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
          setSupportActionBar(toolbar);
  
          FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab);
          fab.setOnClickListener(new View.OnClickListener() {
              @Override
              public void onClick(View view) {
                  Snackbar.make(view, "Replace with your own action", Snackbar.LENGTH_LONG)
                          .setAction("Action", null).show();
              }
          });
  
          DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
          ActionBarDrawerToggle toggle = new ActionBarDrawerToggle(
                  this, drawer, toolbar, R.string.navigation_drawer_open, R.string.navigation_drawer_close);
          drawer.setDrawerListener(toggle);
          toggle.syncState();
  
          NavigationView navigationView = (NavigationView) findViewById(R.id.nav_view);
          navigationView.setNavigationItemSelectedListener(this);
  
          ImageView profile = (ImageView) navigationView.findViewById(R.id.iv_profile);
          profile.setOnClickListener(new View.OnClickListener() { // Null Pointer Exception
              @Override
              public void onClick(View v) {
                  Toast.makeText(v.getContext(), "Profile", Toast.LENGTH_SHORT).show();
              }
          });
      }
  
      @Override
      public void onBackPressed() {
          DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
          if (drawer.isDrawerOpen(GravityCompat.START)) {
              drawer.closeDrawer(GravityCompat.START);
          } else {
              super.onBackPressed();
          }
      }
  
      @Override
      public boolean onCreateOptionsMenu(Menu menu) {
          // Inflate the menu; this adds items to the action bar if it is present.
          getMenuInflater().inflate(R.menu.main, menu);
          return true;
      }
  
      @Override
      public boolean onOptionsItemSelected(MenuItem item) {
          // Handle action bar item clicks here. The action bar will
          // automatically handle clicks on the Home/Up button, so long
          // as you specify a parent activity in AndroidManifest.xml.
          int id = item.getItemId();
  
          //noinspection SimplifiableIfStatement
          if (id == R.id.action_settings) {
              return true;
          }
  
          return super.onOptionsItemSelected(item);
      }
  
      @SuppressWarnings("StatementWithEmptyBody")
      @Override
      public boolean onNavigationItemSelected(MenuItem item) {
          // Handle navigation view item clicks here.
          int id = item.getItemId();
  
          if (id == R.id.nav_camera) {
              // Handle the camera action
          } else if (id == R.id.nav_gallery) {
  
          } else if (id == R.id.nav_slideshow) {
  
          } else if (id == R.id.nav_manage) {
  
          } else if (id == R.id.nav_share) {
  
          } else if (id == R.id.nav_send) {
  
          }
  
          DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
          drawer.closeDrawer(GravityCompat.START);
          return true;
      }
  }
  </code></pre>
  
  <p><strong>activity_main.xml</strong></p>
  
  <pre><code>&lt;?xml version="1.0" encoding="utf-8"?&gt;
  &lt;android.support.v4.widget.DrawerLayout
      xmlns:android="http://schemas.android.com/apk/res/android"
      xmlns:app="http://schemas.android.com/apk/res-auto"
      xmlns:tools="http://schemas.android.com/tools"
      android:id="@+id/drawer_layout"
      android:layout_width="match_parent"
      android:layout_height="match_parent"
      android:fitsSystemWindows="true"
      tools:openDrawer="start"&gt;
  
      &lt;include
          layout="@layout/app_bar_main"
          android:layout_width="match_parent"
          android:layout_height="match_parent"/&gt;
  
      &lt;android.support.design.widget.NavigationView
          android:id="@+id/nav_view"
          android:layout_width="wrap_content"
          android:layout_height="match_parent"
          android:layout_gravity="start"
          android:fitsSystemWindows="true"
          app:headerLayout="@layout/nav_header_main"
          app:menu="@menu/activity_main_drawer"/&gt;
  
  &lt;/android.support.v4.widget.DrawerLayout&gt;
  </code></pre>
  
  <p><strong>app_bar_main.xml</strong></p>
  
  <pre><code>&lt;?xml version="1.0" encoding="utf-8"?&gt;
  &lt;android.support.design.widget.CoordinatorLayout
      xmlns:android="http://schemas.android.com/apk/res/android"
      xmlns:app="http://schemas.android.com/apk/res-auto"
      xmlns:tools="http://schemas.android.com/tools"
      android:layout_width="match_parent"
      android:layout_height="match_parent"
      android:fitsSystemWindows="true"
      tools:context="com.example.heng.progressnfitness.MainActivity"&gt;
  
      &lt;android.support.design.widget.AppBarLayout
          android:layout_width="match_parent"
          android:layout_height="wrap_content"
          android:theme="@style/AppTheme.AppBarOverlay"&gt;
  
          &lt;android.support.v7.widget.Toolbar
              android:id="@+id/toolbar"
              android:layout_width="match_parent"
              android:layout_height="?attr/actionBarSize"
              android:background="?attr/colorPrimary"
              app:popupTheme="@style/AppTheme.PopupOverlay"/&gt;
  
      &lt;/android.support.design.widget.AppBarLayout&gt;
  
      &lt;include layout="@layout/content_main"/&gt;
  
      &lt;android.support.design.widget.FloatingActionButton
          android:id="@+id/fab"
          android:layout_width="wrap_content"
          android:layout_height="wrap_content"
          android:layout_gravity="bottom|end"
          android:layout_margin="@dimen/fab_margin"
          android:src="@android:drawable/ic_dialog_email"/&gt;
  
  &lt;/android.support.design.widget.CoordinatorLayout&gt;
  </code></pre>
  
  <p><strong>nav_header_main.xml</strong></p>
  
  <pre><code>&lt;?xml version="1.0" encoding="utf-8"?&gt;
  &lt;LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
                android:layout_width="match_parent"
                android:layout_height="@dimen/nav_header_height"
                android:background="@drawable/side_nav_bar"
                android:gravity="bottom"
                android:orientation="vertical"
                android:paddingBottom="@dimen/activity_vertical_margin"
                android:paddingLeft="@dimen/activity_horizontal_margin"
                android:paddingRight="@dimen/activity_horizontal_margin"
                android:paddingTop="@dimen/activity_vertical_margin"
                android:theme="@style/ThemeOverlay.AppCompat.Dark"&gt;
  
      &lt;ImageView
          android:id="@+id/iv_profile"
          android:layout_width="wrap_content"
          android:layout_height="wrap_content"
          android:paddingTop="@dimen/nav_header_vertical_spacing"
          android:src="@android:drawable/sym_def_app_icon"/&gt;
  
      &lt;TextView
          android:layout_width="match_parent"
          android:layout_height="wrap_content"
          android:paddingTop="@dimen/nav_header_vertical_spacing"
          android:text="Android Studio"
          android:textAppearance="@style/TextAppearance.AppCompat.Body1"/&gt;
  
      &lt;TextView
          android:id="@+id/textView"
          android:layout_width="wrap_content"
          android:layout_height="wrap_content"
          android:text="android.studio@android.com"/&gt;
  
  &lt;/LinearLayout&gt;
  </code></pre>
  
  <p><strong>content_main.xml</strong></p>
  
  <pre><code>&lt;?xml version="1.0" encoding="utf-8"?&gt;
  &lt;RelativeLayout
      xmlns:android="http://schemas.android.com/apk/res/android"
      xmlns:app="http://schemas.android.com/apk/res-auto"
      xmlns:tools="http://schemas.android.com/tools"
      android:layout_width="match_parent"
      android:layout_height="match_parent"
      android:paddingBottom="@dimen/activity_vertical_margin"
      android:paddingLeft="@dimen/activity_horizontal_margin"
      android:paddingRight="@dimen/activity_horizontal_margin"
      android:paddingTop="@dimen/activity_vertical_margin"
      app:layout_behavior="@string/appbar_scrolling_view_behavior"
      tools:context="com.example.heng.progressnfitness.MainActivity"
      tools:showIn="@layout/app_bar_main"&gt;
  
      &lt;TextView
          android:layout_width="wrap_content"
          android:layout_height="wrap_content"
          android:text="Hello World!"/&gt;
  &lt;/RelativeLayout&gt;
  </code></pre>