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../README.md#Guides

Fabric Native Components

A Fabric Native Component is a Native Component rendered on the screen using the Fabric Renderer. Using Fabric Native Components instead of Legacy Native Components allows us to reap all the benefits of the New Architecture:

  • Strongly typed interfaces that are consistent across platforms.
  • The ability to write your code in C++, either exclusively or integrated with another native platform language, hence reducing the need to duplicate implementations across platforms.
  • The use of JSI, a JavaScript interface for native code, which allows for more efficient communication between native and JavaScript code than the bridge.

A Fabric Native Component is created starting from a JavaScript specification. Then Codegen creates some C++ scaffolding code to connect the component-specific logic (for example, accessing some native platform capability) to the rest of the React Native infrastructure. The C++ code is the same for all the platforms. Once the component is properly connected with the scaffolding code, it is ready to be imported and used by an app.

Essentially the steps for writing a Fabric Native Component are:

  1. Define a JavaScript specification using Flow or TypeScript.
  2. Configure the dependencies management system to generate code from the provided spec.
  3. Implement the Native code.
  4. Integrate the code in the app.

The following section guides you through the creation of a Fabric Native Component, step-by-step, targeting the latest version of React Native.

Note

You can also setup local library containing Fabric Native Component with one command. Read the guide to Local libraries setup for more details.

How to Create a Fabric Native Components

To create a Fabric Native Component, you have to follow these steps:

  1. Define a set of JavaScript specifications.
  2. Configure the component so that Codegen can create the shared code and it can be added as a dependency for an app.
  3. Write the required native code.

Once these steps are done, the component is ready to be consumed by an app. The guide shows how to add it to an app by leveraging autolinking, and how to reference it from the JavaScript code.

1. Folder Setup

In order to keep the component decoupled from the app, it's a good idea to define the module separately from the app and then add it as a dependency to your app later. This is also what you'll do for writing Fabric Native Component that can be released as open-source libraries later.

For this guide, you are going to create a Fabric Native Component that centers some text on the screen.

Create a new folder at the same level of the app and call it RTNCenteredText.

In this folder, create three subfolders: js, ios, and android.

The final result should look like this:

.
├── MyApp
└── RTNCenteredText
    ├── android
    ├── ios
    └── js

2. JavaScript Specification

The New Architecture requires interfaces specified in a typed dialect of JavaScript (either Flow or TypeScript). Codegen uses these specifications to generate code in strongly-typed languages, including C++, Objective-C++, and Java.

There are two requirements the file containing this specification must meet:

  1. The file must be named <MODULE_NAME>NativeComponent, with a .js or .jsx extension when using Flow, or a .ts, or .tsx extension when using TypeScript. Codegen only looks for files matching this pattern.
  2. The file must export a HostComponent object.

Below are specifications of the RTNCenteredText component in both Flow and TypeScript. Create a RTNCenteredTextNativeComponent file with the proper extension in the js folder.

Spec for `RTNCenteredText` in Flow 
// @flow strict-local

import type { ViewProps } from "react-native/Libraries/Components/View/ViewPropTypes";
import type { HostComponent } from "react-native";
import codegenNativeComponent from "react-native/Libraries/Utilities/codegenNativeComponent";

type NativeProps = $ReadOnly<{|
  ...ViewProps,
  text: ?string,
  // add other props here
|}>;

export default (codegenNativeComponent<NativeProps>(
  "RTNCenteredText"
): HostComponent<NativeProps>);
Spec for `RTNCenteredText` in TypeScript 
import type { ViewProps } from "ViewPropTypes";
import type { HostComponent } from "react-native";
import codegenNativeComponent from "react-native/Libraries/Utilities/codegenNativeComponent";

export interface NativeProps extends ViewProps {
  text?: string;
  // add other props here
}

export default codegenNativeComponent<NativeProps>(
  "RTNCenteredText"
) as HostComponent<NativeProps>;

At the beginning of the spec files, there are the imports. The most important imports, required by every Fabric Native Component are:

  • The HostComponent: type the exported component needs to conform to.
  • The codegenNativeComponent function: responsible to actually register the component in the JavaScript runtime.

The second section of the files contains the props of the component. Props (short for "properties") are component-specific information that let you customize React components. In this case, you want to control the text property of the component.

Finally, the spec file exports the returned value of the codegenNativeComponent generic function, invoked passing the name of the component.

Warning

The JavaScript files imports types from libraries, without setting up a proper node module and installing its dependencies. The outcome of this is that the IDE may have troubles resolving the import statements and it can output errors and warnings. These will disappear as soon as the Fabric Native Component is added as a dependency of a React Native app.

3. Component Configuration

Next, you need to add some configuration for Codegen and auto-linking.

Some of these configuration files are shared between iOS and Android, while the others are platform-specific.

Shared

The shared configuration is a package.json file that will be used by yarn when installing your module. Create the package.json file in the root of the RTNCenteredText directory.

{
  "name": "rtn-centered-text",
  "version": "0.0.1",
  "description": "Showcase a Fabric Native Component with a centered text",
  "react-native": "js/index",
  "source": "js/index",
  "files": [
    "js",
    "android",
    "ios",
    "rtn-centered-text.podspec",
    "!android/build",
    "!ios/build",
    "!**/__tests__",
    "!**/__fixtures__",
    "!**/__mocks__"
  ],
  "keywords": ["react-native", "ios", "android"],
  "repository": "https://github.com/<your_github_handle>/rtn-centered-text",
  "author": "<Your Name> <your_email@your_provider.com> (https://github.com/<your_github_handle>)",
  "license": "MIT",
  "bugs": {
    "url": "https://github.com/<your_github_handle>/rtn-centered-text/issues"
  },
  "homepage": "https://github.com/<your_github_handle>/rtn-centered-text#readme",
  "devDependencies": {},
  "peerDependencies": {
    "react": "*",
    "react-native": "*"
  },
  "codegenConfig": {
    "name": "RTNCenteredTextSpecs",
    "type": "components",
    "jsSrcsDir": "js"
  }
}

The upper part of the file contains some descriptive information like the name of the component, its version and its source files. Make sure to update the various placeholders which are wrapped in <>: replace all the occurrences of the <your_github_handle>, <Your Name>, and <your_email@your_provider.com> tokens.

Then there are the dependencies for this package. For this guide, you need react and react-native.

Finally, the Codegen configuration is specified by the codegenConfig field. It contains an array of libraries, each of which is defined by three other fields:

  • name: The name of the library. By convention, you should add the Spec suffix.
  • type: The type of module contained by this package. In this case, it is a Fabric Native Component, thus the value to use is components.
  • jsSrcsDir: the relative path to access the js specification that is parsed by Codegen.

iOS: Create the .podspec file

For iOS, you'll need to create a rtn-centered-text.podspec file which will define the module as a dependency for your app. It will stay in the root of RTNCenteredText, alongside the ios folder.

The file will look like this:

require "json"

package = JSON.parse(File.read(File.join(__dir__, "package.json")))

Pod::Spec.new do |s|
  s.name            = "rtn-centered-text"
  s.version         = package["version"]
  s.summary         = package["description"]
  s.description     = package["description"]
  s.homepage        = package["homepage"]
  s.license         = package["license"]
  s.platforms       = { :ios => "11.0" }
  s.author          = package["author"]
  s.source          = { :git => package["repository"], :tag => "#{s.version}" }

  s.source_files    = "ios/**/*.{h,m,mm,swift}"

  install_modules_dependencies(s)
end

The .podspec file has to be a sibling of the package.json file, and its name is the one we set in the package.json's name property: rtn-centered-text.

The first part of the file prepares some variables that we use throughout the file. Then, there is a section that contains some information used to configure the pod, like its name, version, and description.

All the requirements for the New Architecture have been encapsulated in the install_modules_dependencies. It takes care of installing the proper dependencies based on which architecture is currently enabled. It also automatically installs the React-Core dependency in the old architecture.

Android: build.gradle and the ReactPackage class

To prepare Android to run Codegen you have to:

  1. Update the build.gradle file.
  2. Create a Java/Kotlin class that implements the ReactPackage interface.

At the end of these steps, the android folder should look like this:

android
├── build.gradle
└── src
    └── main
        └── java
            └── com
                └── rtncenteredtext
                    └── CenteredTextPackage.java

The build.gradle file

First, create a build.gradle file in the android folder, with the following contents:

Java 
buildscript {
  ext.safeExtGet = {prop, fallback ->
    rootProject.ext.has(prop) ? rootProject.ext.get(prop) : fallback
  }
  repositories {
    google()
    gradlePluginPortal()
  }
  dependencies {
    classpath("com.android.tools.build:gradle:7.3.1")
  }
}

apply plugin: 'com.android.library'
apply plugin: 'com.facebook.react'

android {
  compileSdkVersion safeExtGet('compileSdkVersion', 33)
  namespace "com.rtncenteredtext"

  defaultConfig {
    minSdkVersion safeExtGet('minSdkVersion', 21)
    targetSdkVersion safeExtGet('targetSdkVersion', 33)
    buildConfigField("boolean", "IS_NEW_ARCHITECTURE_ENABLED", "true")
  }
}

repositories {
  mavenCentral()
  google()
}

dependencies {
  implementation 'com.facebook.react:react-native'
}
Kotlin 
buildscript {
  ext.safeExtGet = {prop, fallback ->
    rootProject.ext.has(prop) ? rootProject.ext.get(prop) : fallback
  }
  repositories {
    google()
    gradlePluginPortal()
  }
  dependencies {
    classpath("com.android.tools.build:gradle:7.3.1")
    classpath("org.jetbrains.kotlin:kotlin-gradle-plugin:1.7.22")
  }
}

apply plugin: 'com.android.library'
apply plugin: 'com.facebook.react'
apply plugin: 'org.jetbrains.kotlin.android'

android {
  compileSdkVersion safeExtGet('compileSdkVersion', 33)
  namespace "com.rtncenteredtext"

  defaultConfig {
    minSdkVersion safeExtGet('minSdkVersion', 21)
    targetSdkVersion safeExtGet('targetSdkVersion', 33)
    buildConfigField("boolean", "IS_NEW_ARCHITECTURE_ENABLED", "true")
  }
}

repositories {
  mavenCentral()
  google()
}

dependencies {
  implementation 'com.facebook.react:react-native'
}

The ReactPackage class

Then, you need a class that implements the ReactPackage interface. To run the Codegen process, you don't have to completely implement the Package class: an empty implementation is enough for the app to pick up the module as a proper React Native dependency and to try and generate the scaffolding code.

Create an android/src/main/java/com/rtncenteredtext folder and, inside that folder, create a CenteredTextPackage.java file.

Java 
package com.rtncenteredtext;

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

import java.util.Collections;
import java.util.List;

public class CenteredTextPackage implements ReactPackage {

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

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

}
Kotlin 
package com.rtncenteredtext

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

class CenteredTextPackage : ReactPackage {
  override fun createViewManagers(reactContext: ReactApplicationContext): List<ViewManager<*, *>> =
    emptyList()

  override fun createNativeModules(reactContext: ReactApplicationContext): List<NativeModule> =
    emptyList()
}

The ReactPackage interface is used by React Native to understand what native classes the app has to use for the ViewManager and Native Modules exported by the library.

4. Native Code

The last step requires you to write some native code to connect the JavaScript side of the Component to what is offered by the platforms. This process requires two main steps:

  1. Run Codegen to see what would be generated.
  2. Write the native code that will make it work.

When developing a React Native app that uses a Fabric Native Component, it is the responsibility of the app to actually generate the code using Codegen. However, when developing a Fabric Component as a library, it needs to reference the generated code, and it is useful to see what the app will generate.

As the first step for both iOS and Android, this guide shows how to execute manually the scripts used by Codegen to generate the required code. Further information on Codegen can be found here.

Warning

The code generated by Codegen in this step should not be committed to the versioning system. React Native apps are able to generate the code when the app is built. This allows an app to ensure that all libraries have code generated for the correct version of React Native.

iOS

Generate the code - iOS

To run Codegen for the iOS platform, open a terminal and run the following command:

cd MyApp
yarn add ../RTNCenteredText
cd ..
node MyApp/node_modules/react-native/scripts/generate-codegen-artifacts.js \
  --path MyApp/ \
  --outputPath RTNCenteredText/generated/ \
  --targetPlatform ios

This script first adds the RTNCenteredText module to the app with yarn add. Then, it invokes Codegen via the generate-codegen-artifacts.js script.

The --path option specifies the path to the app, while the --outputPath option tells the script where to output the generated code.

The output of this process is the following folder structure:

generated
└── build
    └── generated
        └── ios
            ├── FBReactNativeSpec
            │   ├── FBReactNativeSpec-generated.mm
            │   └── FBReactNativeSpec.h
            ├── RCTThirdPartyFabricComponentsProvider.h
            ├── RCTThirdPartyFabricComponentsProvider.mm
            └── react
                └── renderer
                    └── components
                        ├── RTNCenteredTextSpecs
                        │   ├── ComponentDescriptors.h
                        │   ├── EventEmitters.cpp
                        │   ├── EventEmitters.h
                        │   ├── Props.cpp
                        │   ├── Props.h
                        │   ├── RCTComponentViewHelpers.h
                        │   ├── ShadowNodes.cpp
                        │   └── ShadowNodes.h
                        └── rncore
                            ├── ComponentDescriptors.h
                            ├── EventEmitters.cpp
                            ├── EventEmitters.h
                            ├── Props.cpp
                            ├── Props.h
                            ├── RCTComponentViewHelpers.h
                            ├── ShadowNodes.cpp
                            └── ShadowNodes.h

The relevant path for the component is generated/build/generated/ios/react/renderer/components/RTNCenteredTextSpecs. This folder contains all the generated code required by your Component.

See the Codegen section for further details on the generated files.

Note

When generating the scaffolding code using Codegen, iOS does not clean the build folder automatically. If you changed the Spec name, for example, and then run Codegen again, the old files will be retained. If that happens, remember to remove the build folder before running the Codegen again.

cd MyApp/ios
rm -rf build

Write the Native iOS Code

Now that the scaffolding code has been generated, it's time to write the Native code for your Fabric Component. You need to create three files in the RTNCenteredText/ios folder:

  1. The RTNCenteredTextManager.mm, an Objective-C++ file that declares what the Component exports.
  2. The RTNCenteredText.h, a header file for the actual view.
  3. The RTNCenteredText.mm, the implementation of the view.
RTNCenteredTextManager.mm
#import <React/RCTLog.h>
#import <React/RCTUIManager.h>
#import <React/RCTViewManager.h>

@interface RTNCenteredTextManager : RCTViewManager
@end

@implementation RTNCenteredTextManager

RCT_EXPORT_MODULE(RTNCenteredText)

RCT_EXPORT_VIEW_PROPERTY(text, NSString)

@end

This file is the manager for the Fabric Native Component. React Native runtime uses manager objects to register the modules, properties and methods to make them available to the JavaScript side.

The most important call is to the RCT_EXPORT_MODULE, which is required to export the module so that Fabric can retrieve and instantiate it.

Then, you have to expose the text property for the Fabric Native Component. This is done with the RCT_EXPORT_VIEW_PROPERTY macro, specifying a name and a type.

Note

Unlike legacy native components, properties are actually handled via updateProps C++ code, see below. Those macros are needed for bridge compatibility. With bidgeless mode you can omit them entirely. There are other macros that can be used to export custom properties, emitters, and other constructs. You can view the code that specifies them here.

RTNCenteredText.h
#import <React/RCTViewComponentView.h>
#import <UIKit/UIKit.h>

NS_ASSUME_NONNULL_BEGIN

@interface RTNCenteredText : RCTViewComponentView

@end

NS_ASSUME_NONNULL_END

This file defines the interface for the RTNCenteredText view. Here, you can add any native method you may want to invoke on the view. For this guide, you don't need anything, therefore the interface is empty.

RTNCenteredText.mm
#import "RTNCenteredText.h"

#import <react/renderer/components/RTNCenteredTextSpecs/ComponentDescriptors.h>
#import <react/renderer/components/RTNCenteredTextSpecs/EventEmitters.h>
#import <react/renderer/components/RTNCenteredTextSpecs/Props.h>
#import <react/renderer/components/RTNCenteredTextSpecs/RCTComponentViewHelpers.h>

#import "RCTFabricComponentsPlugins.h"

using namespace facebook::react;

@interface RTNCenteredText () <RCTRTNCenteredTextViewProtocol>
@end

@implementation RTNCenteredText {
  UIView *_view;
  UILabel *_label;
}

+ (ComponentDescriptorProvider)componentDescriptorProvider
{
  return concreteComponentDescriptorProvider<RTNCenteredTextComponentDescriptor>();
}

- (instancetype)initWithFrame:(CGRect)frame
{
  if (self = [super initWithFrame:frame]) {
    static const auto defaultProps = std::make_shared<const RTNCenteredTextProps>();
    _props = defaultProps;

    _view = [[UIView alloc] init];
    _view.backgroundColor = [UIColor redColor];

    _label = [[UILabel alloc] init];
    _label.text = @"Initial value";
    [_view addSubview:_label];

    _label.translatesAutoresizingMaskIntoConstraints = false;
    [NSLayoutConstraint activateConstraints:@[
      [_label.leadingAnchor constraintEqualToAnchor:_view.leadingAnchor],
      [_label.topAnchor constraintEqualToAnchor:_view.topAnchor],
      [_label.trailingAnchor constraintEqualToAnchor:_view.trailingAnchor],
      [_label.bottomAnchor constraintEqualToAnchor:_view.bottomAnchor],
    ]];

    _label.textAlignment = NSTextAlignmentCenter;

    self.contentView = _view;
  }

  return self;
}

- (void)updateProps:(Props::Shared const &)props oldProps:(Props::Shared const &)oldProps
{
  const auto &oldViewProps = *std::static_pointer_cast<RTNCenteredTextProps const>(_props);
  const auto &newViewProps = *std::static_pointer_cast<RTNCenteredTextProps const>(props);

  if (oldViewProps.text != newViewProps.text) {
    _label.text = [[NSString alloc] initWithCString:newViewProps.text.c_str() encoding:NSASCIIStringEncoding];
  }

  [super updateProps:props oldProps:oldProps];
}

@end

Class<RCTComponentViewProtocol> RTNCenteredTextCls(void)
{
  return RTNCenteredText.class;
}

This file contains the actual implementation of the view.

It starts with some imports, which require you to read the files generated by Codegen.

The component has to conform to a specific protocol generated by Codegen, in this case, RCTRTNCenteredTextViewProtocol.

Then, the file defines a static (ComponentDescriptorProvider)componentDescriptorProvider method which Fabric uses to retrieve the descriptor provider to instantiate the object.

Then, there is the constructor of the view: the init method. In this method, it is important to create a defaultProps struct using the RTNCenteredTextProps type from Codegen. You need to assign it to the private _props to initialize the Fabric Native Component correctly. The remaining part of the initializer is standard Objective-C code to create views and layout them with AutoLayout.

The last two pieces are the updateProps method and the RTNCenteredTextCls method.

The updateProps method is invoked by Fabric every time a prop changes in JavaScript. The props passed as parameters are downcasted to the proper RTNCenteredTextProps type, and then they are used to update the native code if needed. Notice that the superclass method [super updateProps] must be invoked as the last statement of this method; otherwise the props and oldProps struct will have the same values, and you'll not be able to use them to make decisions and to update the component.

Finally, the RTNCenteredTextCls is another static method used to retrieve the correct instance of the class at runtime.

Warning

Differently from Legacy Native Components, Fabric requires to manually implement the updateProps method. It's not enough to export properties with the RCT_EXPORT_XXX and RCT_REMAP_XXX macros.

Android

Android follows some similar steps to iOS. You have to generate the code, and then you have to write some native code to make it works.

Generate the Code - Android

To generate the code, you need to manually invoke Codegen. This is done similarly to what you need to do for iOS: first, you need to add the package to the app and then you need to invoke a script.

cd MyApp
yarn add ../RTNCenteredText
cd android
./gradlew generateCodegenArtifactsFromSchema

This script first adds the package to the app, in the same way iOS does. Then, after moving to the android folder, it invokes a Gradle task to generate the scaffolding code.

Note

To run Codegen, you need to enable the New Architecture in the Android app. This can be done by opening the gradle.properties files and by switching the newArchEnabled property from false to true.

The generated code is stored in the MyApp/node_modules/rtn-centered-text/android/build/generated/source/codegen folder and it has this structure:

codegen
├── java
│   └── com
│       └── facebook
│           └── react
│               └── viewmanagers
│                   ├── RTNCenteredTextManagerDelegate.java
│                   └── RTNCenteredTextManagerInterface.java
├── jni
│   ├── Android.mk
│   ├── CMakeLists.txt
│   ├── RTNCenteredText-generated.cpp
│   ├── RTNCenteredText.h
│   └── react
│       └── renderer
│           └── components
│               └── RTNCenteredText
│                   ├── ComponentDescriptors.h
│                   ├── EventEmitters.cpp
│                   ├── EventEmitters.h
│                   ├── Props.cpp
│                   ├── Props.h
│                   ├── ShadowNodes.cpp
│                   └── ShadowNodes.h
└── schema.json

You can see that the content of the codegen/jni/react/renderer/components/RTNCenteredTextSpecs looks similar to the files created by the iOS counterpart. The Android.mk and CMakeList.txt files configure the Fabric Native Component in the app, while the RTNCenteredTextManagerDelegate.java and RTNCenteredTextManagerInterface.java files are meant use in your manager.

See the Codegen section for further details on the generated files.

Write the Native Android Code

The native code for the Android side of a Fabric Native Components requires three pieces:

  1. A CenteredText.java that represents the actual view.
  2. A CenteredTextManager.java to instantiate the view.
  3. Finally, you have to fill the implementation of the CenteredTextPackage.java created in the previous step.

The final structure within the Android library should be like this.

android
├── build.gradle
└── src
    └── main
        └── java
            └── com
                └── rtncenteredtext
                    ├── CenteredText.java
                    ├── CenteredTextManager.java
                    └── CenteredTextPackage.java
CenteredText.java
Java 
package com.rtncenteredtext;

import androidx.annotation.Nullable;
import android.content.Context;
import android.util.AttributeSet;
import android.graphics.Color;

import android.widget.TextView;
import android.view.Gravity;

public class CenteredText extends TextView {

    public CenteredText(Context context) {
        super(context);
        this.configureComponent();
    }

    public CenteredText(Context context, @Nullable AttributeSet attrs) {
        super(context, attrs);
        this.configureComponent();
    }

    public CenteredText(Context context, @Nullable AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
        this.configureComponent();
    }

    private void configureComponent() {
        this.setBackgroundColor(Color.RED);
        this.setGravity(Gravity.CENTER_HORIZONTAL);
    }
}
Kotlin 
package com.rtncenteredtext;

import android.content.Context
import android.graphics.Color
import android.util.AttributeSet
import android.view.Gravity
import android.widget.TextView

class CenteredText : TextView {
  constructor(context: Context?) : super(context) {
    configureComponent()
  }

  constructor(context: Context?, attrs: AttributeSet?) : super(context, attrs) {
    configureComponent()
  }

  constructor(context: Context?, attrs: AttributeSet?, defStyleAttr: Int) : super(context, attrs, defStyleAttr) {
    configureComponent()
  }

  private fun configureComponent() {
    setBackgroundColor(Color.RED)
    gravity = Gravity.CENTER_HORIZONTAL
  }
}

This class represents the actual view Android is going to represent on screen. It inherit from TextView and it configures the basic aspects of itself using a private configureComponent() function.

CenteredTextManager.java
Java 
package com.rtncenteredtext;

import androidx.annotation.NonNull;
import androidx.annotation.Nullable;

import com.facebook.react.bridge.ReactApplicationContext;
import com.facebook.react.module.annotations.ReactModule;
import com.facebook.react.uimanager.SimpleViewManager;
import com.facebook.react.uimanager.ThemedReactContext;
import com.facebook.react.uimanager.ViewManagerDelegate;
import com.facebook.react.uimanager.annotations.ReactProp;
import com.facebook.react.viewmanagers.RTNCenteredTextManagerInterface;
import com.facebook.react.viewmanagers.RTNCenteredTextManagerDelegate;

@ReactModule(name = CenteredTextManager.NAME)
public class CenteredTextManager extends SimpleViewManager<CenteredText>
        implements RTNCenteredTextManagerInterface<CenteredText> {

    private final ViewManagerDelegate<CenteredText> mDelegate;

    static final String NAME = "RTNCenteredText";

    public CenteredTextManager(ReactApplicationContext context) {
        mDelegate = new RTNCenteredTextManagerDelegate<>(this);
    }

    @Nullable
    @Override
    protected ViewManagerDelegate<CenteredText> getDelegate() {
        return mDelegate;
    }

    @NonNull
    @Override
    public String getName() {
        return CenteredTextManager.NAME;
    }

    @NonNull
    @Override
    protected CenteredText createViewInstance(@NonNull ThemedReactContext context) {
        return new CenteredText(context);
    }

    @Override
    @ReactProp(name = "text")
    public void setText(CenteredText view, @Nullable String text) {
        view.setText(text);
    }
}
Kotlin 
package com.rtncenteredtext

import com.facebook.react.bridge.ReactApplicationContext
import com.facebook.react.module.annotations.ReactModule
import com.facebook.react.uimanager.SimpleViewManager
import com.facebook.react.uimanager.ThemedReactContext
import com.facebook.react.uimanager.ViewManagerDelegate
import com.facebook.react.uimanager.annotations.ReactProp
import com.facebook.react.viewmanagers.RTNCenteredTextManagerInterface
import com.facebook.react.viewmanagers.RTNCenteredTextManagerDelegate

@ReactModule(name = CenteredTextManager.NAME)
class CenteredTextManager(context: ReactApplicationContext) : SimpleViewManager<CenteredText>(), RTNCenteredTextManagerInterface<CenteredText> {
  private val delegate: RTNCenteredTextManagerDelegate<CenteredText> = RTNCenteredTextManagerDelegate(this)

  override fun getDelegate(): ViewManagerDelegate<CenteredText> = delegate

  override fun getName(): String = NAME

  override fun createViewInstance(context: ThemedReactContext): CenteredText = CenteredText(context)

  @ReactProp(name = "text")
  override fun setText(view: CenteredText, text: String?) {
    view.text = text
  }

  companion object {
    const val NAME = "RTNCenteredText"
  }
}

The CenteredTextManager is a class used by React Native to instantiate the native component. It is the class that implements the interfaces generated by Codegen (see the RTNCenteredTextManagerInterface interface in the implements clause) and it uses the RTNCenteredTextManagerDelegate class.

It is also responsible for exporting all the constructs required by React Native: the class itself is annotated with @ReactModule and the setText method is annotated with @ReactProp.

CenteredTextPackage.java

Finally, open the CenteredTextPackage.java file in the android/src/main/java/com/rtncenteredtext folder and update it with the following lines

Java 
package com.rtncenteredtext;

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

import java.util.Collections;
import java.util.List;

public class CenteredTextPackage implements ReactPackage {

    @Override
    public List<ViewManager> createViewManagers(ReactApplicationContext reactContext) {
+        return Collections.singletonList(new CenteredTextManager(reactContext));
    }

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

}
Kotlin 
package com.rtncenteredtext

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

class CenteredTextPackage : ReactPackage {
  override fun createViewManagers(reactContext: ReactApplicationContext): List<ViewManager<*, *>> =
-   emptyList()
+   listOf(CenteredTextManager(reactContext))

  override fun createNativeModules(reactContext: ReactApplicationContext): List<NativeModule> =
    emptyList()
}

The added lines instantiate a new RTNCenteredTextManager object so that the React Native runtime can use it to render our Fabric Native Component.

5. Adding the Fabric Native Component To Your App

This is the last step to finally see your Fabric Native Component running on your app.

Shared

First of all, you need to add the NPM package which contains the Component to the app. This can be done with the following command:

cd MyApp
yarn add ../RTNCenteredText

This command adds the RTNCenteredText Component to the node_modules of your app.

If the package was previously added to your app, you will need to update it:

cd MyApp
yarn upgrade rtn-centered-text

iOS

Then, you need to install the new dependencies in your iOS project. To do so, you need to run these commands:

cd ios
RCT_NEW_ARCH_ENABLED=1 bundle exec pod install

This command installs the iOS dependencies for the project. The RCT_NEW_ARCH_ENABLED=1 flag instructs CocoaPods that it has to execute some additional operations to run Codegen.

:::note You may have to run bundle install once before you can use RCT_NEW_ARCH_ENABLED=1 bundle exec pod install. You won't need to run bundle install anymore, unless you need to change the ruby dependencies. :::

Android

Android configuration requires to enable the New Architecture.

  1. Open the android/gradle.properties file
  2. Scroll down to the end of the file and switch the newArchEnabled property from false to true.

JavaScript

Finally, you can use the component in your JavaScript application.

Flow 
/**
 * Sample React Native App
 * https://github.com/facebook/react-native
 *
 * @format
 * @flow strict-local
 */
import React from "react";
import type { Node } from "react";
import RTNCenteredText from "rtn-centered-text/js/RTNCenteredTextNativeComponent";

const App: () => Node = () => {
  return (
    <RTNCenteredText
      text="Hello World!"
      style={{ width: "100%", height: 30 }}
    />
  );
};
export default App;
TypeScript 
/**
 * Sample React Native App
 * https://github.com/facebook/react-native
 *
 * @format
 */
import React from "react";
import RTNCenteredText from "rtn-centered-text/js/RTNCenteredTextNativeComponent";

const App: () => JSX.Element = () => {
  return (
    <RTNCenteredText
      text="Hello World!"
      style={{ width: "100%", height: 30 }}
    />
  );
};
export default App;

Now, you can run the React Native app and see your Component on the screen.

Important

This documentation is still experimental and details are subject to changes as we iterate. Feel free to share your feedback on this discussion.

Moreover, it contains several manual steps. Please note that this won't be representative of the final developer experience once the New Architecture is stable. We're working on tools, templates and libraries to help you get started fast on the New Architecture, without having to go through the whole setup.