title: Listener for when the launcher function is called
body: <p>I am working on a Launcher activity and I want when the user presses the home button, it will go to the launcher activity only if the launcher activity is running on screen. 
  Is there a listener for when the launcher function is called? When I say launcher, I mean like the app Nova Launcher where it takes over the home screen when you press home.</p>
  
  <p>My manifest for the activity is set up like so:</p>
  
  <pre><code>&lt;activity
              android:name="com.example.lock.LockscreenActivity"
              android:label="@string/app_name"
              android:theme="@android:style/Theme.NoTitleBar.Fullscreen" 
              android:screenOrientation="portrait"
              android:launchMode="singleInstance"
              android:stateNotNeeded="true"&gt;
              &lt;intent-filter&gt;
                  &lt;action android:name="android.intent.action.MAIN" /&gt;
                  &lt;category android:name="android.intent.category.HOME"/&gt;
                  &lt;category android:name="android.intent.category.DEFAULT" /&gt;
              &lt;/intent-filter&gt;
          &lt;/activity&gt;
  </code></pre>
  
  <p>Or if was as easy as something in the manifest.</p>
  
  <p>Thanks!</p>