Setting Custom User IDs

If your app has its own login system that you want to track users with, you can call setUserId at any time:

amplitude.getInstance().setUserId('USER_ID');

[[Amplitude] instance] setUserId:@"USER_ID"];

Amplitude.getInstance().setUserId("USER_ID");

Amplitude.Instance.setUserId("USER_ID");

You can also add the User ID as an argument to the init call:

amplitude.getInstance().init('API_KEY', 'USER_ID');

[[Amplitude] instance] initializeApiKey:@"API_KEY" userId:@"USER_ID"];

Amplitude.getInstance().initialize(this, "API_KEY", "USER_ID");

Amplitude.Instance.init("API_KEY", "USER_ID");

You should not assign users a User ID that could change as each unique User ID is interpreted as a unique user in Amplitude. Please see our article on how we identify and count unique users for further information.

Logging Out and Anonymous Users

A user's data will be merged on the backend so that any events up to that point from the same browser will be tracked under the same user. If a user logs out or you want to log the events under an anonymous user, you will need to:

1. Set the userId to null.
2. Regenerate a new deviceId.

After doing that, events coming from the current user/device will appear as a brand new user in Amplitude. Note: If you choose to do this, you will not be able to see that the two users were using the same device. Here is an example:

amplitude.getInstance().setUserId(null); // not string 'null'
amplitude.getInstance().regenerateDeviceId();

[[Amplitude instance] setUserId:nil]; // not string nil
[[Amplitude instance] regenerateDeviceId];

Amplitude.getInstance().setUserId(null);
Amplitude.getInstance().regenerateDeviceId();