react-navigation - Cannot read property 'navigate' of undefined - react-navigation

Question

I'm new in React Native and trying create my first app. So I have a question:
I got 2 screens (using react-navigation). At first screen there is a render of app logo with spinner(from native-base) and fetch to the server at the same time. And I need to navigate to another screen only when fetch is over and responce is handled. Please help me find my mistakes!
index.ios.js
import React, { Component } from 'react';
import {
AppRegistry,
StyleSheet,
Text,
View,
TextInput,TouchableHighlight
} from 'react-native';
import { StackNavigator } from 'react-navigation';
import LoadingScreen from './src/screens/LoadingScreen.js';
import MainContainer from './src/screens/MainContainer.js';
export default class Calculator2 extends Component {
render() {
return (
<LoadingScreen/>
);
}
}
const AppNavigator = StackNavigator({
Loading: {
screen: LoadingScreen
},
Main: {
screen: MainContainer
}
});
AppRegistry.registerComponent('Calculator2', () => Calculator2);
LoadingScreen.js:
import React, { Component } from 'react';
import {
AsyncStorage,
AppRegistry,NetInfo,
Text,Image,View
} from 'react-native';
import { StackNavigator } from 'react-navigation';
import AppNavigator from '../../index.ios.js';
import { Container, Header, Content, Spinner } from 'native-base';
export default class LoadingScreen extends Component {
static navigationOptions = {
title: 'Loading',
};
constructor(props){
super(props);
}
componentDidMount(){
const {navigate} = this.props.navigation;
fetch('url').then( (response) => {navigate('Main')});
}
render() {
return(
<View>
App logo with spinner
</View>
);
}
}
MainContainer.js
import React, { Component } from 'react';
import {
AppRegistry,Alert,NetInfo,
StyleSheet,
Text,
View,ActivityIndicator,
TextInput,TouchableHighlight
} from 'react-native';
import { StackNavigator } from 'react-navigation';
import AppNavigator from '../../index.ios.js';
export default class MainContainer extends Component {
static navigationOptions = {
title: 'Main',
};
render() {
return (
<View style={{flexDirection: 'column'}}>
...
</View>
);
}
}
And all I got is an error "Cannot read property 'navigate' of undefined" at LoadingScreen.componentDidMount
UPD
actually my fetch should be a function getting responce and handling it, and it should wait till handling is done:
async function getData(){
var response = await fetch('url', {
method: 'GET'
});
storage = await response.json(); // storage for response
regions = Object.keys(storage); // an array of regions names
console.log(storage, Object.keys(storage));
};

Answer 1

You need to register AppNavigator component instead of Calculator2
AppRegistry.registerComponent('Calculator2', () => AppNavigator);

Answer 2

Just update your LoadingScreen.js's componentDidMount function as following:
componentDidMount() {
var self = this;
fetch('url').then( (response) => {
self.props.navigation.navigate('Main')
});
}