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Native Module Setup

This documentation is a work in progress and version-specific. Please check that the version of this document (top of page) matches the version of RN/RNW you're targeting. Examples (C# and C++/WinRT):

• Native Module Sample in microsoft/react-native-windows-samples
• Sample App in microsoft/react-native-windows/packages/microsoft-reactnative-sampleapps

This guide will help set you up with the Visual Studio infrastructure to author your own stand-alone native module for React Native Windows. In this document we'll be creating the scaffolding for a NativeModuleSample native module.

Development Environment

Make sure you have installed all of the development dependencies.

Choose your own adventure

Once your development environment has been correctly configured, you have several options about how to access native APIs. You can either:

• Reference the APIs directly from within a React Native for Windows project
• Create a new native module library that can be distributed separately from your app
• Add Windows support to an existing community library

Referencing Windows APIs within a React Native for Windows app project

If you are only planning on adding a native module to your existing React Native Windows app, i.e.:

1. You followed the Getting Started guide, where
2. You used the init-windows command to add Windows to your project, and
3. You are just adding your native code to the app project under the windows folder.

Then you can simply open the Visual Studio solution in the windows folder and add the new files directly to the app project.

Creating a new native module library project

The steps to create a new native module library project are:

1. Follow the official React Native instructions to create a blank native module project
2. Add Windows support to the newly created library

Creating a blank native module project

Follow the official React Native instructions at https://reactnative.dev/docs/native-modules-setup,

or execute the following commands:

npx create-react-native-module NativeModuleSample
cd NativeModuleSample
yarn install

Now you'll have a new native module project under NativeModuleSample. Be sure to look at the command output for further steps you'll want to do before publishing the project.

At this point, follow the steps below to add Windows support to the newly created library.

Adding Windows support to an existing library

The steps below are written as if you're working with the NativeModuleSample example above, in the root folder of the project. Substitute the name of the library you're actually working on where appropriate, and ensure that you're working in the appropriate root folder of the library.

Updating your package.json

Many native module libraries (including the default library template) target older versions of react and react-native than Windows supports, so you'll need to upgrade to newer versions in order to add support for react-native-windows.

Properly defining your NPM dependencies is an essential part of creating and maintaining a React Native library, especially one that supports multiple platforms. The instructions here represent the minimum steps required to start targeting react-native-windows. If you're adding Windows support to a library you don't own, you'll need to work with the library owners to make sure any changes made to package.json are appropriate.

For more information on how NPM dependencies work, see Specifying dependencies and devDependencies in a package.json file.

You can use the npm info command to find the correct versions to use. Let's assume you plan on building against the latest stable version of react-native-windows.

Use the following command to find the matching versions of react:

npm info react-native-windows@latest devDependencies.react

Take the result of that command (let's say it's x.y.z) and use it to upgrade the dev dependency:

yarn upgrade react@x.y.z --dev

You'll need to repeat the steps for react-native, i.e.:

npm info react-native-windows@latest devDependencies.react-native

Again, take the result of that command (let's say it's 0.x.y) and use it to upgrade the dev dependency:

yarn upgrade react-native@0.x.y --dev

Next add react-native-windows to your dependencies:

yarn add react-native-windows@latest
yarn install

Now you should be ready to add Windows support with the init-windows command. The process is similar to adding Windows support to an app project, but you'll need to specify a library template:

npx react-native init-windows --template old/uwp-cpp-lib --overwrite

This defaults to a C++/WinRT project. If you want to create a C# based native module project, use:

npx react-native init-windows --template old/uwp-cs-lib --overwrite

That's it, you should be able to open windows\NativeModuleSample.sln and start working on your project.

Testing your Build

To make sure that everything is working, you'll want to try building NativeModuleSample. First you'll want to make sure you've chosen a supported platform:

1. At the top, change the Solution Platform to x86 or x64.
2. In the Build menu, select Build Solution.

Next Steps

You have now created the scaffolding to build a native module or view manager. Now it's time to add the business logic to the module - follow the steps described in the Native Modules and View Managers documents.

Making your module ready for consumption in an app

If you've followed the steps above, your module should be ready for consumption thanks to Autolinking.

However, there are some things you may need to check:

1. Fixing relative NuGet paths

If you are writing a C++/WinRT module and have added any NuGet package dependencies, you'll see references to those packages in your vcxproj file as relative references e.g. ..\packages\.... We need these to use the solution directory instead, so replace all mentions of ..\packages\ with $(SolutionDir)\.

Example:

-<Import Project="..\packages\NuGetPackage.1.0.0.0\build\native\NuGetPackage.props" Condition="Exists('..\packages\NuGetPackage.1.0.0.0\build\native\NuGetPackage.props')" />
+<Import Project="$(SolutionDir)\packages\NuGetPackage.1.0.0.0\build\native\NuGetPackage.props" Condition="Exists('$(SolutionDir)\packages\NuGetPackage.1.0.0.0\build\native\NuGetPackage.props')" />

Testing the module before it gets published

Option 1: Create a new test app

1. Follow the getting started guide to create a new React Native Windows app.
2. Run npm i <module-local-path> --save (e.g. npm i D:\NativeModuleSample --save) to install the local module.
3. Link the native module.

Option 2: Adding Windows support to existing sample app

If you are working on an existing module that already has iOS and Android samples, and want to add Windows support to the existing test app, follow these steps (example of WebView module test app can be found here).

1. In a different directory, follow the getting started guide and create a new React Native Windows app.
2. Copy the Windows folder from the blank RNW app into the existing sample app's sample app's folder. (The RNW CLI helps create the correct project setup that you can then copy directly into the sample app.)
3. Open sln and vxcproj files and check node_module reference paths. Fix the paths if necessary based on how the folders are structured in native module repo (example).
4. Open the solution with Visual Studio and link native module.

The project should build correctly at this point, but we still need to setup some special metro configurations for Windows in order to run the app without breaking iOS and Android bundling.

5. Add metro.config.windows for Windows bundling (example). Make sure the config file is at the root of the repo (see Metro bug #588).
6. In package.json, add a separate start command for windows and attach a special argument to tell metro to use the windows config we just created (example).
7. Add react-native.config.js to parse the special argument we added (example).
8. Update JS main module path (relative path to metro projectRoot) in App.cpp if necessary (example).

Adding tests for your module

We are using WebdriverIO + WinAppDriver for UI testing. More details here. For real world examples, check out react-native-webview or progress-view.

Setup CI (continuous integration) pipeline for your module

When done developing your module, it's good practice to setup a CI pipeline with automated build and tests to avoid any future regressions. See the Setup Continuous Integration Pipeline for an RNW App for more information.

Documenting Your Module

Once your module is complete, update react-native-community/directory so that its information on your native module is up to date. If you are building a native module which will be maintained by Microsoft, please update the Supported Community Modules documentation in react-native-windows-samples with your native module's information.