title: Data is unavaliable before render in react native
body: <p>i'm trying to pull data from the permanent storage on the beginning of my app, and then use this data to run a login function, but the data isn't avaliable when i try to run the function.
  Example: </p>
  
  <pre><code>import store from 'react-native-simple-store'
  
  class ExampleScreen extends Component {
    constructor(props) {
      super(props)
      this.state = {
        username: "",
        password: ""
      }
  
    componentWillMount(){
      try {
        store.get('User').then((User) =&gt; this.setState({username: User}));
        store.get('Pass').then((Pass) =&gt; this.setState({password: Pass}));
      } catch(error){
        alert(error)
      };
      this.onSubmitPress;
    }
  
    onSubmitPress = async () =&gt; {
      alert(this.state.username);
      alert(this.state.password);
    }
  }
  
  </code></pre>
  
  <p>The function returns the empty state set on the beginning ("").</p>
  
  <p>How can i run a function with the data i get before the render?</p>
  
  <p>Edit1: I need the data before the render to run the login function before i render the login screen.
  I tried run on ComponentDidMount() but the data isn't avaliable until the render process starts (I can render this.state.username as a text on the render)</p>