# Bridging Native & React for iOS & Android

## js -> native

### Simple one-off example

Keep in mind:
- `RCT_EXPORT_METHOD` exposes the name of the method up to the __first__ colon in js land.
- When many methods share the same name, use `RCT_REMAP_METHOD` to define a different name for js and map it to the native method. ie. `RCT_REMAP_METHOD(differentMethodName, methodName:(BOOL)arg1 arg2:(BOOL)arg2)`.

#### React

```js
import { NativeModules } from 'react-native'
var videoPlayer = NativeModules.VideoPlayer
videoPlayer.seekTo(100)
```

#### iOS

[docs](http://facebook.github.io/react-native/releases/next/docs/native-modules-ios.html#ios-calendar-module-example)

```objc
// VideoPlayer.h
#import <React/RCTBridgeModule.h>

@interface VideoPlayer : NSObject <RCTBridgeModule>
@end

@implementation VideoPlayer
RCT_EXPORT_MODULE(); // or RCT_EXPLORT_MODULE(AwesomeVideoPlayer) -- custom name

RCT_EXPORT_METHOD(seekTo:(double)time)
{
  // seek to time
}
@end
```

#### Android

[docs](http://facebook.github.io/react-native/releases/next/docs/native-modules-android.html#the-toast-module)

```java
// VideoPlayer.java
package com.beme.react

import com.facebook.react.bridge.NativeModule;
import com.facebook.react.bridge.ReactApplicationContext;
import com.facebook.react.bridge.ReactContext;
import com.facebook.react.bridge.ReactContextBaseJavaModule;
import com.facebook.react.bridge.ReactMethod;

public class VideoModule extends ReactContextBaseJavaModule {
  public VideoModule(ReactApplicationContext reactContext) {
    super(reactContext)
  }

  @Override
  public String getName() {
    return "VideoPlayer";
  }

  @ReactMethod
  public void seekTo(double time) {
    // seek to time
  }
}
```

Register the module

```java
// VideoPackage.java
package com.beme.react

import com.facebook.react.ReactPackage;
import com.facebook.react.bridge.JavaScriptModule;
import com.facebook.react.bridge.NativeModule;
import com.facebook.react.bridge.ReactApplicationContext;
import com.facebook.react.uimanager.ViewManager;

public class VideoPackage implements ReactPackage {
  @Override
  public List<Class<? extends JavaScriptModule>> createJSModules() {
    return Collections.emptyList();
  }

  @Override
  public List<ViewManager> createViewManagers(ReactApplicationContext reactContext) {
    return Collections.emptyList();
  }

  @Override
  public List<NativeModule> createNativeModules(
                              ReactApplicationContext reactContext) {
    List<NativeModule> modules = new ArrayList<>();
    modules.add(new VideoModule(reactContext));
    return modules;
  }
}
```

```java
// MainApplication.java
protected List<ReactPackage> getPackages() {
    return Arrays.<ReactPackage>asList(
            new MainReactPackage(),
            new VideoPackage()); // <-- Add this line with your package name.
}
```

### Callbacks

#### React

```javascript
// index.ios.js
videoPlayer.seekTo(100, (error, someData) => {
  if (error) {
    console.error(error)
  } else {
    console.log(someData)
  }
})

// index.android.js
videoPlayer.seekTo(
  100, 
  (msg) => {
    console.error(msg)
  }, 
  (someData) => {
    console.log(someData)
  }
)
```

#### iOS

[docs](http://facebook.github.io/react-native/releases/next/docs/native-modules-ios.html#callbacks)

```objc
RCT_EXPORT_METHOD(seekTo:(double)time callback:(RCTResponseSenderBlock)callback)
{
  NSArray *someData;
  callback(@[[NSNull null], someData]); // (error, someData) in js
}
```

#### Android

[docs](http://facebook.github.io/react-native/releases/next/docs/native-modules-android.html#callbacks)

```java
@ReactMethod
public void seekTo(double time, Callback errorCallback, Callback successCallback) {
  try {
    successCallback.invoke(someData);
  } catch (Exception e) {
    errorCallback.invoke(e.getMessage());
  }
}
```

### Promises

#### React

```javascript
async function loadVideo() {
  try {
    var videoLoaded = await VideoPlayer.loadVideo();
    this.setState(videoLoaded: videoLoaded)
  } catch (e) {
    console.error(e)
  }
}

loadVideo()
```

#### iOS

[docs](http://facebook.github.io/react-native/releases/next/docs/native-modules-ios.html#promises)

```objc
RCT_REMAP_METHOD(loadVideo, loadVideoResolver:(RCTPromiseResolveBlock)resolve rejecter:(RCTPromiseRejectBlock)reject)
{
  BOOL videoLoaded = ...
  if (videoLoaded) {
    resolve(videoLoaded);
  } else {
    NSError *error = ...
    reject(@"error", @"error description", error);
  }
}
```

#### Android

```java
```

### Properties (UI)

## native -> js

### Events

Keep in mind:
- Events share namespace (so come up with a naming convention)
- If you have several instances of a component, you need to pass an identifier (like a view's `reactTag`) to identify it in the handler.

## Additional Resources