constructor(props) {
    super(props);
    // add reference to database
    this.itemsRef = firebaseApp.database().ref('/name')
    //
    this.state = {
      int_data: [3,4,5,6,7,8,9],
      data_source: "",
      connected: true,
    }
  }

  // itemsRef'e event handler eklemek için
  addItemsRefListener(itemsRef) {
    // items ref'e value degisme durumunu handle edecek bir listener ekle
    itemsRef.on('value', (snap) => {

      if (snap.val()){
        this.setState({data_source: snap.val()});
      }
      // datasource'u guncelle

    });
  }
  componentWillMount() {
    NetInfo.isConnected.fetch().then(res => this.setState({connected:res})).catch(err => console.log(err));
  }

  componentDidMount() {
    // component yüklendiğinden itemsRef'e listener ekle
    this.addItemsRefListener(this.itemsRef);
    if(!this.state.connected){
      ToastAndroid.show("No Internet Connection", ToastAndroid.SHORT);
    }
  }

  render() {
    if(this.state.connected) {
      return (
        <View>
          <ToolbarAndroid style={styles.toolbarElement} title="Welcome to My App" actions={[{title:"Settings", show:'always'}]} onActionSelected={this.onActionSelected}/>
          <Navigator></Navigator>
          <Text>
            {this.state.data_source}
          </Text>