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According to my research, starting in API 23, you can change the app you use when you hold down the home button. Any ideas on how to get my assistant as an option? Thanks in advance. (The issue is I cannot find code to make this work)
The setting is usually at Settings/Apps (or App Manager)/Configure apps (three dots icon)/Assist & voice input/assist app
You can implement a personal assistant just like the Google Now on Tap using the Assist API starting Android 6.0. The official developer (http://developer.android.com/training/articles/assistant.html) guide tells exactly how you should implement it.