title: calling function on Picker item Selection react native
body: <p>I am trying to call a <code>function</code> whenever i select an item from <code>picker</code> and display the selected item with <code>alert</code>.<br>
  Here's what i am doing :- </p>
  
  <pre><code>import React, { Component } from 'react';
  import { AppRegistry, StyleSheet, TextInput, View, Alert, Button,Platform,ActivityIndicator, Text, Picker, ScrollView } from 'react-native';
  export default class FirstProject extends Component {
     constructor(props) {
    super(props);
    this.state = {
      isLoading: true,
      throttlemode:'',
    }
  }
  GetSelectedThrottleModeItem=(throttlemode)=&gt;{
  Alert.alert(this.state.throttlemode)
  }
  render() {
  return (
      &lt;View style={styles.MainContainerAddCamp}&gt;
      &lt;Text style={{fontSize: 12}}&gt; Throttle Mode&lt;/Text&gt;
      &lt;Picker style={styles.PickerStyleClass}
    selectedValue={this.state.throttlemode}
    onValueChange={(throttlemodeValue, throttlemodeIndex) =&gt; this.GetSelectedThrottleModeItem(this.setState({throttlemode:throttlemodeValue}))}&gt;
      &lt;Picker.Item label="Asap" value="asap" /&gt;
      &lt;Picker.Item label="Even" value="even" /&gt;
      &lt;/Picker&gt;
     &lt;/View&gt;
    );
  }
  }
  const styles = StyleSheet.create({
  MainContainerAddCamp :{
  flex:1,
  margin: 10,
  paddingTop: (Platform.OS === 'ios') ? 20 : 20,
  padding: 5,
  },
  TextInputStyleClass: {
  textAlign: 'left',
  paddingLeft: 7,
  marginBottom: 7,
  height: 40,
  borderWidth: 1,
  borderColor: '#00BCD4',
  },
  PickerStyleClass:{
      backgroundColor:'#87ceeb',
      paddingLeft: 7,
  marginBottom: 7,
  height: 40,
  borderWidth: 1,
   borderColor: '#FF5722',
  }
  });
  </code></pre>
  
  <p>This code is displaying the previously selected value. How can i make it to display current selected value.<br>
  Please suggest where i have missed. </p>