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# FFIgen + JNIgen pedometer
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This is a demo for some of our tooling around
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calling platform APIs directly from dart code.
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This repository represents a demo of a plugin that leverages FFIgen & JNIgen.
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There is also an example pedometer app that
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uses the bindings generated from these tools.
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- [FFIgen](https://pub.dev/packages/ffigen) is used to generate
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bindings for C, Objective-C and Swift APIs.
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- [JNIgen](https://pub.dev/packages/jnigen) is used to generate
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bindings for Java and Kotlin APIs.
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**These tools are both experimental and are currently a work in progress.**
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If you find any issues or have feedback,
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please file it on the corresponding GitHub repositories.
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## Re-generating bindings
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The bindings that allow the Dart code to call the platform code have
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already been generated in the [`\lib` folder](./lib).
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You can regenerate them by following the steps below:
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### FFIgen
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Configuration of FFIgen for the
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[CoreMotion framework](https://developer.apple.com/documentation/coremotion)
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is in the [`ffigen.yaml` file](./ffigen.yaml).
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FFIgen currently does not support autogenerating code to handle callbacks.
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So, there are a few extra steps needed to
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appropriately handle callbacks in Objective-C.
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You can read more about this limitation on
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[dart.dev](https://dart.dev/interop/objective-c-interop#callbacks-and-multithreading-limitations).
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```bash
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dart run ffigen --config ffigen.yaml
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```
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### JNIgen
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Configuration of JNIgen for the
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[HealthConnect API](https://developer.android.com/guide/health-and-fitness/health-connect)
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is in the [`jnigen.yaml` file](./jnigen.yaml).
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1. Build an Android APK file from the example app.
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Currently, JNIgen requires at least one APK build
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to obtain the classpaths of Android Gradle libraries.
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```bash
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cd example && flutter build apk
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```
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2. Return to the `/pedometer` directory and run `jnigen`:
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```bash
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cd .. && dart run jnigen --config jnigen.yaml
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```
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## Running the example app
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The example app is located in the [`/example`](./example) directory,
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and the following commands assume they are being run from that location.
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Note that step counting is only available on physical devices.
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### iOS
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- Run `flutter run` and choose your physical device.
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- Allow the *pedometer* app access to step counting.
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### Android
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- Make sure that [Google Fit](https://play.google.com/store/apps/details?id=com.google.android.apps.fitness)
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is installed (to ensure that steps are being counted).
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- Run `flutter run` and choose your physical device.
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- Install [Health Connect](https://play.google.com/store/apps/details?id=com.google.android.apps.healthdata)
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and grant access to Google Fit and the *jni_demo* app.
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## Project structure
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* `src`: Contains the native source code, and a `CMakeLists.txt` file for
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building that source code into a dynamic library.
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* `lib`: Contains the Dart code that defines the API of the plugin and
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calls into the native code using `dart:ffi`.
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* platform folders (`ios` etc.): Contain the build files for
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building and bundling the native code library with the platform application.
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* `example`: Contains the native source code for building
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that source code into a dynamic library.
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