# Bridge Existing iOS & Android Apps with React Native
## Today - Our path to React Native - Overview of Embedded React Native - Problems - Solutions - Problems - Solutions - Thoughts on our future
## We Needed - A screen rewrite existing in iOS/Android companion apps - Nearly double the screens in those apps - On both platforms - Within ~3 weeks
## What About React Native? - Consolidate UI - Double developer resources - Leverage Yoga (_flexbox_) to fit our design - Remotely affect UI/functionality?

Demo

Which parts are React Native?

## Where Is Best? - Leave existing code intact - New UIViewControllers, Activities - New UIViews, Fragments
## Where Is Trouble? - Installation will [probably] be a pain - Days in our case - Heavy API integration within the UI - Slows integration - Support of very old Android devices - Erodes features & responsiveness
## The Installation Process - Generally able to - [Follow docs on facebook.github.io][0] - But... [0]: http://facebook.github.io/react-native/releases/0.46/docs/integration-with-existing-apps.html
## Separate Repos - To leverage React testing - To accomodate separate languages/structures - To allow for separate release cycles ~~~ ~/src/ |_ ios-field-staff |_ android-field-staff |_ rn-field-staff ~~~
## iOS Installation - Clone iOS - Install latest cocoapods - Clone RN - Install node modules - Symlink to iOS repo - Start RN bundle server - Run iOS simulator
## Android Installation - Clone Android - Update and gradle install - Clone RN - Install node modules - Symlink to Android repo - Start RN bundle server - Run Android simulator
## Embedded React Native An overview of React Native and native communication ~~~ Props +----------------+ <----------------+ | | | | React Native | | | View | +--------+---------+ | | | | +-------+--------+ | Native Control | | | | | +----------+ +------------------+ +--> | | | Native | | Bridge | | | +----------+ ~~~
## Where Is Your Time Spent? - 1/3 in React Native - 1/3 building bridges - 1/3 massaging props
## Loading RN Views - Construct with the native lifecycle in mind - Build a dedicated function to create props - With empty state as default
## Loading iOS RN View Instantiate the RN view with [bare] props ~~~swift class RunningLateViewController: UIViewController { var runningLateViewRN: RCTRootView? var runningLateViewRNURL = "an URL or bundle" override func loadView() { super.loadView() self.runningLateViewRN = RCTRootView( bundleURL: self.runningLateViewRNURL, moduleName: "RunningLate", initialProperties: self.buildProps() as [NSObject : AnyObject], launchOptions: nil ) self.view = self.runningLateViewRN! } // ... } ~~~
## Loading iOS RN View, Continued Asynchronous loading of new props ~~~swift //... class RunningLateViewController: UIViewController { // ... func buildProps(cleaning) -> NSDictionary { // build our props here... } func fetchAPICall() { // call our api, then... DispatchQueue.main.async() { (self.view as! RCTRootView).appProperties = self.buildProps() as [NSObject : AnyObject] } } } ~~~
## Loading Android RN View Instantiate the RN view with [bare] props ~~~java public class RNRunningLateActivity extends AppCompatActivity { private ReactRootView mReactRootView; private ReactInstanceManager mReactInstanceManager; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_rn_running_late); mReactInstanceManager = ReactInstanceManagerAPI.getInstance() .buildReactInstanceManager("running-late.shared.bundle", "running-late.shared.js"); mReactRootView = (ReactRootView) findViewById(R.id.react_root); mReactRootView.startReactApplication(mReactInstanceManager, "RunningLateShared", this.buildProps(null)); } // ... } ~~~
## Loading Android RN View, Continued Asynchronous loading of new props ~~~java public class RNRunningLateActivity extends AppCompatActivity { // ... private Bundle buildProps(JSONArray data) { // Build props... } void fetchAPICall() { // call api, then... Bundle props = buildProps(data); mReactRootView.setAppProperties(props); } // ... } ~~~
## Loading Android RN View, Continued Start asynchronous props in native lifecycle ~~~java public class RNRunningLateActivity extends AppCompatActivity { // ... @Override protected void onResume() { super.onResume(); if (mReactInstanceManager != null) { mReactInstanceManager.onHostResume(this, this); } fetchAPICall(); } @Override protected void onPause() { super.onPause(); if (mReactInstanceManager != null) { mReactInstanceManager.onHostPause(this); } } @Override protected void onDestroy() { super.onDestroy(); if (mReactInstanceManager != null) { mReactInstanceManager.onHostDestroy(); } } @Override public void invokeDefaultOnBackPressed() { if (mReactInstanceManager != null) { mReactInstanceManager.onBackPressed(); } else { super.onBackPressed(); } } } ~~~
## Example RN View Such lovely, concise UI logic ~~~js export default class RunningLateShared extends React.PureComponent { // ... render() { return ( <View style={styles.container}> <Text style={styles.shiftTime}> {formatTime(this.props.shift.start)} </Text> {this.renderAvatar(styles.staffImageWrapTop)} <View style={styles.noteView}> {!this.state.submitted && // ... } {this.state.submitted && // ... } </View> </View> ); } } ~~~
## Building Bridges - Get in. - Get out. - Embrace the _single direction_ of props
## Example React Native Bridge Always check for bridge methods ~~~js import { NativeModules } from 'react-native'; const bridge = NativeModules.CurrentCleaningBridge; const isImplemented = (name) => { if (!bridge || !bridge[name]) { console.log(name, 'bridge not implemented'); return false; } return true; } export const componentDidMount = () => { if (!isImplemented('componentDidMount')) return; bridge.componentDidMount(); }; ~~~
## Example React Native Bridge With Args Always fall back to default args ~~~js import { NativeModules } from 'react-native'; const bridge = NativeModules.CurrentCleaningBridge; export const onSubmit = (note) => { if (!isImplemented('onSubmit')) return; bridge.onSubmit(note || ''); }; export const onRootLayout = (x, y, width, height) => { if (!isImplemented('onRootLayout')) return; bridge.onRootLayout(x || 0, y || 0, width || 0, height || 0); }; ~~~
## Example React Native Bridge Usage Call the bridge as you would HTTP ~~~js export default class Foo extends React.PureComponent { _onLayout = (event) => { const { x, y, width, height } = event.nativeEvent.layout; bridge.onRootLayout(x, y, width, height); } render() { return ( <View onLayout={this._onLayout}> </View> } } ~~~
## Example Swift iOS Bridge - Leverage Swift - Expose modules in Objective-C
## Obj-C Bridge Implementation Decalre visisble methods and args ~~~objc #import "CurrentCleaningBridgingHeader.h" #import "React/RCTBridgeModule.h" @interface RCT_EXTERN_MODULE(CurrentCleaningBridge, NSObject) RCT_EXTERN_METHOD(onSubmit:(NSString * __nonnull)note) RCT_EXTERN_METHOD(onRootLayout:(NSNumber * __nonnull)x y:(NSNumber * __nonnull)y width:(NSNumber * __nonnull)width height:(NSNumber * __nonnull)height) RCT_EXTERN_METHOD(componentDidMount) @end ~~~
## Obj-C Bridge Header Defer to Swift auto-gen headers ~~~objc // Look to the Swift definition... #ifndef CurrentCleaningBridgingHeader_h #define CurrentCleaningBridgingHeader_h #import "React/RCTBridge.h" #import "React/RCTBridgeModule.h" #import "React/RCTEventDispatcher.h" #endif ~~~
## Swift Bridge Handle basic message passing ~~~swift import Foundation import Firebase @objc(CurrentCleaningBridge) class CurrentCleaningBridge: NSObject { @objc func componentDidMount() -> Void { // good for nothing... } @objc func onRootLayout(_ x: NSNumber, y: NSNumber, width: NSNumber, height: NSNumber) -> Void { RNEmbeddedViews.shared() .triggeredLayout(RootView: "CurrentCleaning", x: x, y: y, width: width, height: height) } } ~~~
## Swift Bridge, Continued Delegate actual logic to other objects ~~~swift @objc(CurrentCleaningBridge) class CurrentCleaningBridge: NSObject { //... @objc func onSubmit(_ note: NSString) -> Void { FIRAnalytics.logEvent(withName: Constant.Analytics.Events.updateCheckinNote, parameters: [:]) StaffAPIClient.sharedClient() .updateCurrentCheckinNote(note: note as String) { (checkin, error) in if (error != nil) { // Handle err.... } } } } ~~~
## Example Java Android Bridge Declare namespace and accept context ~~~java // import ... public class CurrentCleaningBridge extends ReactContextBaseJavaModule { private static final String TAG = "CurrentCleaningBridge"; public CurrentCleaningBridge(ReactApplicationContext reactContext) { super(reactContext); } @Override public String getName() { return "CurrentCleaningBridge"; } } ~~~
## Example Java Android Bridge, Continued Handle basic message passing ~~~java public class CurrentCleaningBridge extends ReactContextBaseJavaModule { // ... @ReactMethod public void componentDidMount() { // good for nothing... } @ReactMethod public void onRootLayout(float x, float y, float width, float height) { CurrentCleaningSingleton.getInstance() .onRootLayout("CurrentCleaning", x, y, width, height); } } ~~~
## Example Java Android Bridge, Continued Delegate actual logic to other objects ~~~java public class CurrentCleaningBridge extends ReactContextBaseJavaModule { // ... @ReactMethod public void onSubmitNote(String note) { StaffAPI.getInstance() .updateCheckinNote(getReactApplicationContext(), note, new APICallbackInterface() { @Override public void onResponse(VolleyError error, JSONObject response) { if (error != null) { // handle error... } } }); } } ~~~
## Communicating to Parent View - Special bridge case - Bridges are ad-hoc instances - How to tell a parent of variable resize?
## RN Bridge Singleton A way to communicate back to our parent ~~~ Props +----------------+ <----------------+ | | | | React Native | | | View | +--------+---------+ | | | | +-------+--------+ | Native Control | | | | | +----------+ +------------------+ +--> | | | Native | ^ | Bridge | | | +-----------+ +----------+ Bridge Singleton ~~~
## Example Java Embedded View Singleton Declare interface and create singleton ~~~java public interface RNEmbeddedViewInterface { void onRootLayout(String rootView, float x, float y, float width, float height); } public class RNEmbeddedViewSingleton { private static final RNEmbeddedViewSingleton ourInstance = new RNEmbeddedViewSingleton(); public static RNEmbeddedViewSingleton getInstance() { return ourInstance; } private RNEmbeddedViewSingleton() { } // ... } ~~~
## Example Java Embedded View Singleton Handle listener registration ~~~java // ... public class RNEmbeddedViewSingleton { // ... private RNEmbeddedViewInterface mListener; public void registerListener(RNEmbeddedViewInterface listener) { this.mListener = listener; } public void removeListener(RNEmbeddedViewInterface listener) { if (mListener == listener) { this.mListener = null; } } // ... } ~~~
## Example Java Embedded View Singleton, Continued Call listener with bridge method ~~~java // RNEmbeddedViewSingleton.getInstance().registerListener(this); public class RNEmbeddedViewSingleton { //... public void onRootLayout(String rootView, float x, float y, float width, float height) { if (mListener == null) { return; } mListener.onRootLayout(rootView, x, y, width, height); } } ~~~
## Example Swift Embedded View Singleton Declare interface and class ~~~swift struct RNViewLayout { let x: NSNumber let y: NSNumber let width: NSNumber let height: NSNumber } protocol RNEmbeddedViewsDelegate { func onLayout(RootView: NSString, dimensions: RNViewLayout) } class RNEmbeddedViews: NSObject { // ... } ~~~
## Example Swift Embedded View Singleton, Continued Configure delegate registration ~~~swift // ... class RNEmbeddedViews: NSObject { var delegate: RNEmbeddedViewsDelegate? class func shared() -> RNEmbeddedViews { struct Singleton { static let instance = RNEmbeddedViews() } return Singleton.instance } // ... // RNEmbeddedViews.shared().delegate = self } ~~~
## Example Swift Embedded View Singleton, Continued Call delegate with bridge method ~~~swift // ... class RNEmbeddedViews: NSObject { // ... func triggeredLayout(RootView: NSString, x: NSNumber, y: NSNumber, width: NSNumber, height: NSNumber) { let dimensions = RNViewLayout(x: x, y: y, width: width, height: height) self.delegate?.onLayout(RootView: RootView, dimensions: dimensions) } } ~~~
## Finding Platform Differences - Custom navigation control - Text inputs - Tactile inputs - Accessibility features - Some flexbox layouts - Overlapping fails on Android - Conflicts with Flat UI
## Juggling Platform Differences - Platform wrappers with shared.js within ~~~ ____________ ___________ | android.js | | ios.js | | | | | | loads ____|_|____ loads | |_______| shared.js |______| | | | Main UI | |___________| ~~~
## Debugging Crash Reports - iOS has been easy - Pain & confusion - `Caused by: java.lang.IllegalArgumentException:` - Serialization too large? - Bad memory cleanup?
## Future Requests - Break down the debug wall - Better docs on embedded usage - Reproducible installations - Upgrade paths - Ability to pre-render views
## Future Prospects - All apps in React Native? - Is native development still relevant? - What will our next app contain? _We are not enemies, but friends. We must not be enemies._
## Get Started - Create a RN repo - Link to your native app(s) - Choose a simple view/fragment - Rewrite it in React - Pass it props - Build a bridge - Repeat!
## Thanks! https://www.andjosh.com/presents https://officeluv.github.io