使用 AWS Amplify Android 检查用户是否已存在？

Question

Is there way to check if a user exists, before trying to sign them up? When I try to signing up an existing username, it causes an error. Here's the current method I'm using, but it doesn't work.

private View.OnClickListener registerClickListener = new View.OnClickListener() {
    @Override
    public void onClick(View v) {
        cognitoUser = userPool.getUser(Username.getText().toString());
        if (cognitoUser.getUserId().isEmpty()) {
            Amplify.Auth.signUp(
                Username.getText().toString(),
                Password.getText().toString(),
                AuthSignUpOptions.builder()
                    .userAttribute(AuthUserAttributeKey.email(), Email.getText().toString())
                    .build(),
                result -> Log.i("AuthQuickStart", "Result: " + result.toString()),
                error -> Log.e("AuthQuickStart", "Sign up failed", error)
            );
        } else {
            Toast.makeText(getApplicationContext(), "Username is taken", Toast.LENGTH_SHORT)
                .show();
            Username.requestFocus();
        }
    }
};

Answer 1

To be able to use the GetUser API call you need a valid AccessToken . And for that you already need to be authenticated. So you can't use it this way.

Also, Cognito currently does not offer a simple way of checking if user already exists.

So your only option is to rely on exceptions thrown by the sign up action.