class LoginScreen extends Component {

   static PropTypes = {
      dispatch: PropTypes.func,
      fetching: PropTypes.bool,
      attemptLogin: PropTypes.func
   }

   isAttempting = false

   constructor (props) {
     super(props)

      this.state = {
        username: '',
        password: '',
        isLoaded: {false}
      }

   }

   componentDidMount(){
     const { username, password } = this.state
     this._getSavedUsername();

     // AsyncStorage
     //   .getItem('@MobAppCorpStore:username')
     //   .then((v_username) => { this.setState({ username: v_username, isLoaded: true  }) });

   }

   async _getSavedUsername() {
     const { username } = this.state

     try {
       const value = await AsyncStorage.getItem('@MobAppCorpStore:username');
       if (value !== null){
         this.setState({ username: value});
       }
     } catch (error) {
       // Error retrieving data
       alert('Containers/LoginScreen - _getSavedUsername error')
       console.log('Containers/LoginScreen - get username error : ', error)
     }
   }

   ...

   render () {
      ...

      <Form style={styles.form_style}>
         <Item floatingLabel >
            <Label>{I18n.t('Global.username')}</Label>
            <Input
                  style={styles.input_style}
                  //autoFocus = {true}
                  returnKeyType='next'
                  value={username}
                  onChangeText={username => this.setState({username})}
                  autoCapitalize="none"
                  blurOnSubmit={false}
                  />
         </Item>
         <Item floatingLabel last >
            <Label>{I18n.t('Global.password')}</Label>
            <Input
                  style={styles.input_style}
                  returnKeyType='go'
                  secureTextEntry={true}
                  value={password}
                  onChangeText={password => this.setState({password})}
                  onSubmitEditing={this._handlePressLogin}
                  autoCapitalize="none"/>
         </Item>
       </Form>

       ...
   }

   ...

}

Warning: Can't call setState (or forceUpdate) on an unmounted component.
This is a no-op, but it indicates a memory leak in your application. To fix,
cancel all subscriptions and asynchronous tasks in the componentWillUnmount
method.