要检查是否是用户首次登录，只需在OnCompleteListener.onComplete回调中调用AdditionalUserInfo.isNewUser()方法.

To check if it's the first time user logs in, simply call the AdditionalUserInfo.isNewUser() method in the OnCompleteListener.onComplete callback.

下面的示例代码，请务必检查是否为空.

Example code below, be sure to check for null.

OnCompleteListener<AuthResult> completeListener = new OnCompleteListener<AuthResult>() {
        @Override
        public void onComplete(@NonNull Task<AuthResult> task) {
            if (task.isSuccessful()) {
                boolean isNew = task.getResult().getAdditionalUserInfo().isNewUser();
                Log.d("MyTAG", "onComplete: " + (isNew ? "new user" : "old user"));
            }
        }
    };

检查文档以获取更多参考信息 AdditionalUserInfo

Check the docs for more reference AdditionalUserInfo