If you want to start Google Now on Nexus devices, you swipe-up with a simple gesture from the navbar. I want go replace this feature with my own app. if you swipe the, app-p
Add the following <intent-filter>
to the Activity you want launched from the gesture:
<intent-filter>
<action android:name="android.intent.action.ASSIST" />
<category android:name="android.intent.category.DEFAULT" />
</intent-filter>
You will now see an option for your app when you make the swipe now, and will have to select it as the default handler by selecting Always, as shown below.
It's just a matter of setting the correct intent filter:
<intent-filter>
<action android:name="android.intent.action.ASSIST"/>
<category android:name="android.intent.category.DEFAULT"/>
</intent-filter>