如何使用非字符串引用而不导致流错误

我发现字符串引用是react中的遗留内容: https://github.com/yannickcr/eslint-plugin-react/blob/master/docs/rules/no-string-refs.md

但我的组件中出现了这个流错误,不知道如何解决它:

[flow] Cannot assign `c` to `this.loginform` because property `loginform` is missing in `LoginScreen` [1]. (References: [1])

我的组件:

/**
 * @flow
 */

// ... imports, tcomb form model, etcetera ...

class LoginScreen extends React.Component<*> {

  onPress() {
    var creds = this.loginform.getValue();
    orbRequestLogin(this.props.navigation, creds, '/oauth/token');
  }

  render() {
    return (
      <Wrap bgcolor="white">
        <Content>
          <KeyboardAvoidingView behavior="padding">
            <Form ref={(c) => { this.loginform = c; }} type={User} options={options} />

            <TouchableHighlight style={styles.button} onPress={this.onPress.bind(this)}>
              <Text style={styles.buttonText}>Log in</Text>
            </TouchableHighlight>

          </KeyboardAvoidingView>
        </Content>
      </Wrap>
    );
  }
}

export default withNavigation(LoginScreen);