title: android - Enable and Disable MenuItem on Navigation Drawer Activity Layout
body: <p>I have and app created using the Navigation Drawer <code>Activity</code> Layout.. And I need to <strong>enable/disable</strong> some items programmatically</p>
  
  <p><a href="http://i.stack.imgur.com/oO2BF.jpg" rel="noreferrer">Menu Example</a></p>
  
  <p>Example: I want to disable the Menu Item id nav_item2</p>
  
  <p>I tried to do...</p>
  
  <pre><code>MenuItem nav_item2 = (MenuItem)findViewById(R.id.nav_item2);
  nav_item2.setEnabled(false);
  </code></pre>
  
  <p>And it return a <strong>NullPointerException</strong> to me..</p>
  
  <p>Also tried...</p>
  
  <pre><code>@Override
  public boolean onPrepareOptionsMenu(Menu menu) {
      super.onPrepareOptionsMenu(menu);
      nav_item2 = menu.findItem(R.id.nav_item2);
      return true;
  }
  </code></pre>
  
  <p>with the same <strong>NullPointerException</strong></p>
  
  <p>Someone know something to do?</p>
  
  <p>nav_header_main_activity.xml (Generated with the Layout Creation)</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/imageView"
          android:layout_width="199dp"
          android:layout_height="72dp"
          android:paddingTop="@dimen/nav_header_vertical_spacing"
          android:src="@drawable/ciag" /&gt;
  
      &lt;TextView
          android:layout_width="match_parent"
          android:layout_height="wrap_content"
          android:paddingTop="@dimen/nav_header_vertical_spacing"
          android:text="CIAg"
          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="dev@ciag.org.br" /&gt;
  
  &lt;/LinearLayout&gt;
  </code></pre>
  
  <p>main_activity_navigation_drawer.xml (generated on the layout creation)</p>
  
  <p>
  </p>
  
  <pre><code>&lt;group android:checkableBehavior="single"&gt;
      &lt;item
          android:id="@+id/nav_save"
          android:icon="@android:drawable/ic_menu_save"
          android:enabled="false"
          android:title="@string/nav_save" /&gt;
      &lt;item
          android:id="@+id/nav_graph"
          android:icon="@drawable/chart_bar"
          android:enabled="false"
          android:title="@string/nav_graph" /&gt;
      &lt;item
          android:id="@+id/nav_send"
          android:icon="@drawable/ic_menu_send"
          android:title="Enviar" /&gt;
  &lt;/group&gt;
  
  &lt;item android:title="Configurações"&gt;
      &lt;menu&gt;
          &lt;item
              android:id="@+id/nav_manage"
              android:icon="@drawable/ic_menu_manage"
              android:enabled="false"
              android:title="@string/nav_manage" /&gt;
          &lt;item
              android:id="@+id/nav_support"
              android:icon="@android:drawable/ic_menu_help"
              android:title="@string/nav_support" /&gt;
      &lt;/menu&gt;
  &lt;/item&gt;
  </code></pre>
  
  <p></p>