Rethinking Navigation

An exploration of a component-first API for React Navigation for building more dynamic navigation solutions.

Considerations

• Should play well with static type system
• Navigation state should be contained in root component (helpful for stuff such as deep linking)
• Component-first API

Building blocks

NavigationContainer

Component which wraps the whole app. It stores the state for the whole navigation tree.

useNavigationBuilder

Hook which can access the navigation state from the context. Along with the state, it also provides some helpers to modify the navigation state provided by the router. All state changes are notified to the parent NavigationContainer.

Router

An object that provides a reducer to update the state as well as some action creators.

Navigator

Navigators bundle a router and a view which takes the navigation state and decides how to render it.

A simple navigator could look like this:

function StackNavigator({ initialRouteName, children, ...rest }) {
  // The `navigation` object contains the navigation state and some helpers (e.g. push, pop)
  // The `descriptors` object contains the screen options and a helper for rendering a screen
  const { navigation, descriptors } = useNavigationBuilder(StackRouter, {
    initialRouteName,
    children,
  });

  return (
    // The view determines how to animate any state changes
    <StackView navigation={navigation} descriptors={descriptors} {...rest} />
  );
}

The navigator can render a screen by calling descriptors[route.key].render(). Internally, the descriptor wraps the screen in a NavigationStateContext.Provider to support nested state:

<NavigationStateContext.Provider state={route.state}>
  <MyComponent />
</NavigationStateContext.Provider>

Basic usage

function App() {
  return (
    <NavigationContainer>
      <StackNavigator initialRouteName="home">
        <Screen name="settings" component={Settings} />
        <Screen
          name="profile"
          component={Profile}
          options={{ title: 'John Doe' }}
        />
        <Screen name="home">
          {() => (
            <TabNavigator initialRouteName="feed">
              <Screen name="feed" component={Feed} />
              <Screen name="article" component={Article} />
              <Screen name="notifications">
                {props => <Notifications {...props} />}
              </Screen>
            </TabNavigator>
          )}
        </Screen>
      </StackNavigator>
    </NavigationContainer>
  );
}

Navigators need to have Screen components as their direct children. These components don't do anything by themselves, but the navigator can extract information from these and determine what to render. Implementation-wise, we'll use React.Children API for this purpose.

Initial state

In the current implementation of React Navigation, the initial state is extracted from the navigator definitions. This is possible because they are defined statically. In our case, it's not possible because the screens are rendered dynamically.

Turns out we don't really need the initial state in the NavigationContainer. This state is the default state, so we can store undefined instead, and let the navigators initialize their initial state themselves. Next time an action modifies the state, we update the value in the container.

If an initial state is specified, e.g. as a result of Linking.getInitialURL(), the child navigators will use that state, instead of having to initialize it themselves.