如何在Cognito中检查现有用户-Android?

所以我在Android中设置了aws cognito.而且我想执行检查以查看用户何时输入用户名，该用户名在我的认知池中尚不存在.

so i have aws cognito set up in android. And i want to perform a check to see when the user enters a username, that that username doesn't already exist in my cognito pool.

目前我有这个:

 cognitoUser = userPool.getUser(username_ET.getText().toString());
 if(cognitoUser.getUserId().isEmpty())
 {
      //Great, this is a new user.
 }

但是，cognitoUser只是设置为我输入的内容，它不会返回检查.

But, cognitoUser just gets set to whatever i put in, it doesn't go back in check.

希望有人可以提供帮助！

Hope someone can help!