This tutorial aims to get you up to speed with writing iOS apps using React Native. If you're wondering what React Native is and why Facebook built it, this [blog post](https://code.facebook.com/posts/1014532261909640/react-native-bringing-modern-web-techniques-to-mobile/) explains that.
react-native-cli is a command line interface that does the rest of the set up. It’s installable via npm. This will install `react-native`as a command in your terminal. You only ever need to do this once.
You can now open this new project (`AwesomeProject/AwesomeProject.xcodeproj`) in Xcode and simply build and run it with cmd+R. Doing so will also start a node server which enables live code reloading. With this you can see your changes by pressing cmd+R in the simulator rather than recompiling in Xcode.
`react-native init` will copy `Examples/SampleProject` to whatever you named your project, in this case AwesomeProject. This is a simple hello world app. You can edit `index.ios.js` to make changes to the app and then press cmd+R in the simulator to see the changes.
Before we write the code to fetch actual Rotten Tomatoes data let's mock some data so we can get our hands dirty with React Native. At Facebook we typically declare constants at the top of JS files, just below the requires, but feel free to add the following constant wherever you like. In `index.ios.js`:
We're going to render the title, year, and thumbnail for the movie. Since thumbnail is an Image component in React Native, add Image to the list of React requires below.
Press cmd+R and you should see "Title" above "2015". Notice that the Image doesn't render anything. This is because we haven't specified the width and height of the image we want to render. This is done via styles. While we're changing the styles let's also clean up the styles we're no longer using.
Great, we've rendered our data. Now let's make it look better. I'd like to put the text to the right of the image and make the title larger and centered within that area:
Not too much has changed, we added a container around the Texts and then moved them after the Image (because they're to the right of the Image). Let's see what the style changes look like:
We use FlexBox for layout - see [this great guide](https://css-tricks.com/snippets/css/a-guide-to-flexbox/) to learn more about it.
In the above code snippet, we simply added `flexDirection: 'row'` that will make children of our main container to be layed out horizontally instead of vertically.
This means that the `rightContainer` takes up the remaining space in the parent container that isn't taken up by the Image. If this doesn't make sense, add a `backgroundColor` to `rightContainer` and then try removing the `flex: 1`. You'll see that this causes the container's size to be the minimum size that fits its children.
Add some initial state to our application so that we can check `this.state.movies === null` to determine whether the movies data has been loaded or not. We can set this data when the response comes back with `this.setState({movies: moviesData})`. Add this code just above the render function inside our React class.
We want to send off the request after the component has finished loading. `componentDidMount` is a function of React components that React will call exactly once, just after the component has been loaded.
Now add `fetchData` function used above to our main component. This method will be respondible for handling data fetching. All you need to do is call `this.setState({movies: data})` after resolving the promise chain because the way React works is that `setState` actually triggers a re-render and then the render function will notice that `this.state.movies` is no longer `null`. Note that we call `done()` at the end of the promise chain - always make sure to call `done()` or any errors thrown will get swallowed.
Now press cmd+R and you should see "Loading movies..." until the response comes back, then it will render the first movie it fetched from Rotten Tomatoes.
Why is a `ListView` better than just rendering all of these elements or putting them in a `ScrollView`? Despite React being fast, rendering a possibly infinite list of elements could be slow. `ListView` schedules rendering of views so that you only display the ones on screen and those already rendered but off screen are removed from the native view hierarchy.
You'll notice we used `dataSource` from `this.state`. The next step is to add an empty `dataSource` to the object returned by `getInitialState`. Also, now that we're storing the data in `dataSource`, we should not longer use `this.state.movies` to avoid storing data twice. We can use boolean property of the state (`this.state.loaded`) to tell whether data fetching has finished.
There's still some work to be done to make it a fully functional app such as: adding navigation, search, infinite scroll loading, etc. Check the [Movies Example](https://github.com/facebook/react-native/tree/master/Examples/Movies) to see it all working.
