Mobile apps rarely consist of just one scene (another word for screen). As soon as you add a second scene to your app, you will have to take into consideration how the user will navigate from one scene to the other.
You can use navigators to transition between multiple scenes. These transitions can be typical side-to-side animations down a master/detail stack, or vertical modal popups.
React Native has several built-in navigation components, but for your first app you will probably want to use `Navigator`. It provides a JavaScript implementation of a navigation stack, so it works on both iOS and Android and is easy to customize.
Something you will encounter a lot when dealing with navigation is the concept of routes. A route is an object that contains information about a scene. It is used to provide all the context that the navigator's `renderScene` function needs to render a scene. A basic `Navigator` implementation may look like this:
The above example will display a single scene, but in order to push a new scene onto screen you will need to learn about `push` and `pop`. These two methods are provided by the `navigator` object that is passed to your `renderScene` function. They can be used, as you may have realized, to push and pop routes into your navigation stack.
In this example, the `MyScene` component is passed the title of the current route via the `title` prop. It displays two tappable components that call the `onForward` and `onBack` functions passed through its props, which in turn will call `navigator.push()` and `navigator.pop()` as needed.
While this is a very basic example, it can easily be adapted to render an entirely different component based on the route that is passed to the `renderScene` function. Navigator will push new scenes from the right by default, and you can control this behavior by using the `configureScene` function. You can also configure a navigation bar through the `navigationBar` prop.
Check out the [Navigator API reference](docs/navigator.html) for more code samples.
If you are targeting iOS only, you may also want to consider using [NavigatorIOS](docs/navigatorios.html). It looks and feels just like [`UINavigationController`](https://developer.apple.com/library/ios/documentation/UIKit/Reference/UINavigationController_Class/), because it is actually built on top of it.
Just like Navigator, NavigatorIOS uses routes to represent scenes, with some important differences. The actual component that will be rendered can be specified using the `component` key in the route, and any props that should be passed to this component can be specified in `passProps`. A "navigator" object is automatically passed as a prop to the component, allowing you to call `push` and `pop` as needed.
As NavigatorIOS leverages native UIKit navigation, it will automatically render a navigation bar with a back button and title.
> You may also want to check out [react-native-navigation](https://github.com/wix/react-native-navigation), a component that aims to provide native navigation on both iOS and Android.
## NavigationExperimental
Navigator and NavigatorIOS are both stateful components. If your app has multiple of these, it can become tricky to coordinate navigation transitions between them. NavigationExperimental provides a different approach to navigation, allowing any view to act as a navigation view and using reducers to manipulate state at a top-level object. It is bleeding edge as the name implies, but you might want to check it out if you are craving greater control over your app's navigation.
```js
<NavigationCardStack
onNavigateBack={onPopRouteFunc}
navigationState={myNavigationState}
renderScene={renderSceneFun}
/>
```
You can import NavigationExperimental like any other component in React Native. Once you have that, you can deconstruct any additional components from NavigationExperimental that you may find useful. Since I am feeling like building navigation stacks today, I'll go ahead and pick out NavigationCardStack and NavigationStateUtils.
```js
import React, { Component } from 'react';
import { NavigationExperimental } from 'react-native';
const {
CardStack: NavigationCardStack,
StateUtils: NavigationStateUtils,
} = NavigationExperimental;
```
As I said earlier, NavigationExperimental takes a different approach than Navigator and NavigatorIOS. Using it to build a navigation stack requires a few more steps than the stateful components, but the payoff is worth it.
### Step 1. Define Initial State and Top Level Component
Create a new component for your application. This will be the top-level object, so we will define the initial state here. The navigation state will be defined in the `navigationState` key, where we define our initial route:
```js
class BleedingEdgeApplication extends Component {
constructor(props, context) {
super(props, context);
this.state = {
// This defines the initial navigation state.
navigationState: {
index: 0, // Starts with first route focused.
routes: [{key: 'My Initial Scene'}], // Starts with only one route.
<Text>This is a placeholder. We will come back to this and render our navigation here later.</Text>
);
}
}
```
Alright, now we have a simple stateful component that doesn't do much at all. We can change that. Our initial state contains one route, and the current index. That looks suspiciously just like our initial route definition in Navigator. Do you remember which actions its navigator object provided?
Push and pop, of course. That seems pretty straightforward to implement. I promised you earlier we would be using reducers to manage state at the top-level object. Sit tight.
### Step 2. Reducing the Navigation State
NavigationExperimental comes built-in with a some useful reducers, and they are all available as part of NavigationStateUtils. The two we will be using right now are called -- yep -- push and pop. They take a navigationState object, and return a new navigationState object.
We can use them to write our `_onNavigationChange` function which, given a "push" or "pop" action, will reduce the state accordingly.
```js
_onNavigationChange(type) {
// Extract the navigationState from the current state:
let {navigationState} = this.state;
switch (type) {
case 'push':
// Push a new route, which in our case is an object with a key value.
// I am fond of cryptic keys (but seriously, keys should be unique)
const route = {key: 'Route-' + Date.now()};
// Use the push reducer provided by NavigationStateUtils
Cool. I'm getting the hang of this. This is the heart of NavigationExperimental. We are only handling two actions here, but a more complex application could also take into account a "back" action (e.g. Android back button), as well as handle the transition between several tabs in a tabbed application.
I am still missing the initial scene that will be rendered (as well as the actual navigator that will wrap it, but lets not get ahead of ourselves).
### Step 3. Define Scenes
First I want to define a Row component out of convenience. It displays some text and can call some function when pressed.
```js
class TappableRow extends Component {
render() {
return (
<TouchableHighlight
style={styles.row}
underlayColor="#D0D0D0"
onPress={this.props.onPress}>
<Textstyle={styles.buttonText}>
{this.props.text}
</Text>
</TouchableHighlight>
);
}
}
```
Now I will define my actual scene. It uses a scroll view to display a vertical list of items. The first row displays the current route's key, and two more rows will call our theoretical navigator's push and pop functions.
```js
class MyVeryComplexScene extends Component {
render() {
return (
<ScrollViewstyle={styles.scrollView}>
<Textstyle={styles.row}>
Route: {this.props.route.key}
</Text>
<TappableRow
text="Tap me to load the next scene"
onPress={this.props.onPushRoute}
/>
<TappableRow
text="Tap me to go back"
onPress={this.props.onPopRoute}
/>
</ScrollView>
);
}
}
```
### Step 4. Create a Navigation Stack
Now that I have defined the state and a function to manage it, I think I can go ahead and create a proper navigator component now. While I'm at it, I'll render my scene after configuring it with the current route's props.
```js
class MyVerySimpleNavigator extends Component {
// This sets up the methods (e.g. Pop, Push) for navigation.
You are now an expert navigator. Take a look at [NavigationExperimental in UIExplorer](https://github.com/facebook/react-native/tree/master/Examples/UIExplorer/NavigationExperimental) to learn how to implement other types of navigation hierarchies, such as a tabbed application with multiple navigation stacks.
