title: Show alert box using redux observable
body: <p>I am using redux observable in my react native application, On my login screen I want to show a react native alert dialog box if credentials are not valid. Can i fire alert in my epic but in epic I can only return an observable, so how to achieve this using redux observable ?</p>
  
  <ul>
  <li>Update 01</li>
  </ul>
  
  <p>Authentication code:</p>
  
  <pre><code>export const signInFailure = (payload) =&gt; {
    return {
      type: SIGN_IN_FAILURE,
      payload
    }
  };
  
  
  const signInSuccessActions = (payload) =&gt; {
  return Observable.concat(
      Observable.of({type: SIGN_IN_SUCCESS, payload}),
      Observable.of({type: 'Navigation/NAVIGATE', routeName:          'MainTabView'})
  );
   };
  
  
  export const signInRequestEpic = action$ =&gt;
  action$.ofType(SIGN_IN_REQUEST)
      .mergeMap(action =&gt; AuthService.login(action.email,  action.password)
          .flatMap(payload =&gt; payload.status === 200 ?  signInSuccessActions(payload) : signInFailure(payload))
          .catch(error =&gt; Observable.of({
              type: SIGN_IN_FAILURE,
              error
          }))
      );
  </code></pre>
  
  <p>Using alert api in react native is just 1 liner</p>
  
  <pre><code>import {Alert} from "react-native";
  
   Alert.alert(
          'Invalid',
          'Email or password incorrect',
      )
  </code></pre>