已安装的Google Play应用列表(List of installed apps from Google Play)

I use the Cloud Save feature of Google Play Services for this functionality. Google Description of Cloud Save implementation

When the user first logs in to my program, I use getAppStateClient().listStates to see if the State Key even exists (for me, sometimes it does not "auto" tell me that the State Key Doesn't exist, so I don't rely on that functionality)

If the key doesn't exist, then I know they've never used the program before, so, then I can add the key with whatever value (for you, perhaps only add the key after they have completed the login/setup process... or whatever would work for your flow)

If the key does exist, then I have different values that I store there to tell me what prior information the user has entered (for you, could set if they completed Login Process or not, last time they logged in... etc)