react-native-firebase/codorials/authentication-with-firebase/app-navigation.md

App Navigation

React Navigation has gone through many cycles of navigation implementations and has been a pain point for developers for a good while. A current "go to" navigation library is called react-navigation. It's pure JavaScript implementation which performs well and provides a solid foundation for navigation on both Android and iOS.

Authentication typically requires 3 screens; Login, Register & Forgot Password.

Installation

Simply install the dependency via NPM, no native installation is needed:

npm install --save react-navigation

Navigation Stacks

Navigation on an app typically works in stacks, where a user can navigate to a new screen (pushing a new screen onto the stack), or backwards (popping a screen off the stack).

What's great about this concept is that we can create multiple instances of a stack, for example a stack for unauthenticated users and another for authenticated ones.

To create a new stack, we import the StackNavigator from react-navigation. In it's basic form, the first item of the StackNavigator object acts as our initial screen on the stack. Lets create a new directory and component for our unauthenticated state:

// src/screens/unauthenticated/index.js

import { StackNavigator } from 'react-navigation';

import Login from './Login';
import Register from './Register';

export default StackNavigator({
  Login: {
    screen: Login,
  },
  Register: {
    screen: Register,
  }
});

In both the Login & Register files, create a basic React component (change Login to Register where appropriate):

// src/screens/unauthenticated/Login.js
// src/screens/unauthenticated/Register.js

import React, { Component } from 'react';
import { View, Text } from 'react-native';

class Login extends Component {
  render() {
    return (
      <View>
        <Text>
          Login
        </Text>
      </View>
    );
  }
}

Using the stack

StackNavigator returns a React component which can be rendered in our app. If we go back to our src/App.js component, we can now return the stack:

// src/App.js

import React, { Component } from 'react';

import UnauthenticatedStack from './screens/unauthenticated';

class App extends Component {

    render() {
      return <UnauthenticatedStack />;
    }

}

export default App;

Our UnauthenticatedStack component will now show the Login component as it's the first item in the StackNavigator. Reload your app and you should have your Login component rendering!


Styling the navigator

As you can see, react-navigation provides basic styling to mimic the feel of Android's Material Design. The library provides a simple, React like API to style and control your app.

If you're using iOS, the functionality will remain the same however the basic styling will represent that of the iOS interface instead!

For this example we're going to add a title to our screen and liven up the colors - there's loads more you can do with react-navigation though, just check out their in-depth documentation.

Lets go ahead and style the screen, using a class static navigationOptions object which lets react-navigation access our screen component:

// src/screens/unauthenticated/Login.js

import React, { Component } from 'react';
import { View, Text } from 'react-native';

class Login extends Component {

  // Add our react-navigation static method:
  static navigationOptions = {
    title: 'Login',
    headerStyle: {
      backgroundColor: '#E6853E',
    },
    headerTintColor: '#fff',
  };

  render() {
    return (
      <View>
        <Text>
          Login
        </Text>
      </View>
    );
  }
}

export default Login;

With this basic config you'll end up with an Android looking app with minimal configuration. Whats better is that react-navigation will also take care of any back buttons and screen animations when navigating through the stack, pretty nifty.


Pushing to a new stack

Pushing a new screen onto the stack is a common practice on mobile apps, however requires a slightly different mindset if you're from a web development background. The basics of a stack allow you to push and pop where screens effectively overlay each other. The user cannot change stack item unless you give them the ability to (compared to a website where the user could manually enter a different URL). This allows for greater control over what a user is able to push/pop to.

Each component we assign to our StackNavigator gets cloned by react-navigation with a prop called navigation which gives us full control over all of the navigation functionality we'll need.

• To "push" to a new screen we call the navigate method with the screen name we defined as the object key within StackNavigator.
• To "pop", or go back to the previous screen on the stack we call the goBack method.

Lets add a simple button to push to the Register screen we defined:

// src/screens/unauthenticated/Login.js
import React, { Component } from 'react';
import { View, Button } from 'react-native';

class Login extends Component {

  static navigationOptions = {
    title: 'Login',
    headerStyle: {
      backgroundColor: '#E6853E',
    },
    headerTintColor: '#fff',
  };

  // Call this method on the button press
  _register = () => {
    this.props.navigation.navigate('Register');
  };

  render() {
    return (
      <View>
        <Button
          onPress={this._register}
          title="Register Now!"
        />
      </View>
    );
  }
}

export default Login;

Go ahead and click the button, you'll be pushed to a new screen. By pressing the back arrow on the header, react-navigation will automatically call the goBack method for us:


To style the Register page, simply add it's own navigationOptions static config!