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-picker comes and asks you which app do you want to start: my app or Google Now. How can I implement this?
I have found an example which runs without root.
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.