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
The router object provides various helper methods to deal with the state and actions, a reducer to update the state as well as some action creators.
The router is responsible for handling actions dispatched by calling methods on the navigation object. If the router cannot handle an action, it can return null, which would propagate the action to other routers until it's handled.
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 { state, navigation, descriptors } = useNavigationBuilder(StackRouter, {
initialRouteName,
children,
});
return (
// The view determines how to animate any state changes
<StackView
state={state}
navigation={navigation}
descriptors={descriptors}
{...rest}
/>
);
}
export default createNavigator(StackNavigator);
The navigator can render a screen by calling descriptors[route.key].render(). Internally, the descriptor adds appropriate wrappers to handle nested state.
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.
Basic usage
const Stack = StackNavigator();
const Tab = TabNavigator();
function App() {
return (
<NavigationContainer>
<Stack.Navigator initialRouteName="home">
<Stack.Screen name="settings" component={Settings} />
<Stack.Screen
name="profile"
component={Profile}
options={{ title: 'John Doe' }}
/>
<Stack.Screen name="home">
{() => (
<Tab.Navigator initialRouteName="feed">
<Tab.Screen name="feed" component={Feed} />
<Tab.Screen name="article" component={Article} />
<Tab.Screen name="notifications">
{props => <Notifications {...props} />}
</Tab.Screen>
</Tab.Navigator>
)}
</Stack.Screen>
</Stack.Navigator>
</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 use React.Children API for this purpose.
The content to render can be specified in 2 ways:
- React component in
componentprop (recommended) - Render callback as children
When a React component is specified, the navigator takes care of adding a React.memo to prevent unnecessary re-renders. However, it's not possible to pass extra props to the component this way. It's preferable to use the context API for such cases instead of props.
A render callback which doesn't have such limitation and is easier to use for this purpose. However, performance optimization for the component is left to the user in such case.
The rendered component will receives a navigation prop with various helpers and a route prop which represents the route being rendered.
Setting screen options
In React Navigation, screen options can be specified in a static property on the component (navigationOptions). This poses few issues:
- It's not possible to configure options based on props, state or context
- To update the props based on an action in the component (such as button press), we need to do it in a hacky way by changing params
- It breaks when used with HOCs which don't hoist static props, which is a common source of confusion
Instead of a static property, we expose a method to configure screen options:
function Selection({ navigation }) {
const [selectedIds, setSelectedIds] = React.useState([]);
navigation.setOptions({
title: `${selectedIds.length} items selected`,
});
return <SelectionList onSelect={id => setSelectedIds(ids => [...ids, id])} />;
}
This allows options to be changed based on props, state or context, and doesn't have the disadvantages of static configuration.
Type-checking
The library exports few helper types. Each navigator also need to export a custom type for the navigation prop which should contain the actions they provide, .e.g. push for stack, jumpTo for tab etc.
Currently type checking and intelliSense works for route name and params. The user has to define a type alias with a list of routes along with the type of params they use.
For our example above, we need 2 separate types for stack and tabs:
type StackParamList = {
settings: undefined;
profile: { userId: string };
home: undefined;
};
type TabParamList = {
feed: undefined;
article: undefined;
notifications: undefined;
};
In a component, it's possible to annotate the navigation and route props using these types:
type Props = {
navigation: StackNavigationProp<StackParamList, 'profile'>;
route: RouteProp<StackParamList, 'profile'>;
};
function Profile(props: Props) {
// Content
}
Annotating the navigation prop will be enough for provide type-checking for actions such as navigate etc. Annotating route will provide type-checking for accessing params for the current route.
For nested navigators, the navigation prop is a combination of multiple navigation props, so we need to combine multiple types to type them. We export a type called CompositeNavigationProp to make it easier:
type FeedScreenNavigationProp = CompositeNavigationProp<
TabNavigationProp<TabParamList, 'feed'>,
StackNavigationProp<StackParamList>
>;
The CompositeNavigationProp type takes 2 parameters, first parameter is the primary navigation type (type for the navigator that owns this screen) and second parameter is the secondary navigation type (type for a parent navigator). The primary navigation type should always have the screen's route name as it's second parameter.
For multiple parent navigators, this secondary type should be nested:
type FeedScreenNavigationProp = CompositeNavigationProp<
TabNavigationProp<TabParamList, 'feed'>,
CompositeNavigationProp<
StackNavigationProp<StackParamList>,
DrawerNavigationProp<DrawerParamList>
>
>;
It's also possible to type-check the navigator to some extent. To do this, we need to pass a generic when creating the navigator object:
const Stack = StackNavigator<StackParamList>();
And then we can use it:
<Stack.Navigator initialRouteName="profile">
<Stack.Screen name="settings" component={Settings} />
<Stack.Screen
name="profile"
component={Profile}
options={{ title: 'My profile' }}
/>
<Stack.Screen name="home" component={Home} />
</Stack.Navigator>
Unfortunately it's not possible to verify that the type of children elements are correct since TypeScript doesn't support type-checking JSX elements.