要检查是否是用户第一次登录，只需调用 OnCompleteListener 中的 AdditionalUserInfo.isNewUser() 方法.onComplete 回调.

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，一定要检查是否为空.

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"));
            }
        }
    };

查看文档以获取更多参考AdditionalUserInfo

Check the docs for more reference AdditionalUserInfo