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viam_flutter_nmea

A way to use the gonmea package in Flutter

Getting Started

This package contains the Go implementation where it is using the gonmea package to parse nmea readings. To build an app that consumes this package, do the following:

  • Run ./build_go.sh to generate the header file which will be used by the ffigen package to generate dart bindings.

  • cd src then run make ios to generate the ios binaries for both simulator and physical iPhone devices.

  • Run make android to generate binaries for different android architectures.

  • In the root directory of the project, run flutter pub run ffigen --config ffigen.yaml to auto-generate the dart bindings from the header file

  • All the implementation for the public facing API exists in the lib/flutter_nmea_impl.dart file.

  • There is an example app to help test the implementation. cd example && flutter run to run the example app

Project structure

This template uses the following structure:

  • src: Contains the native source code, and a CmakeFile.txt file for building that source code into a dynamic library.

  • lib: Contains the Dart code that defines the API of the plugin, and which calls into the native code using dart:ffi.

  • platform folders (android, ios, windows, etc.): Contains the build files for building and bundling the native code library with the platform application.

Building and bundling native code

The pubspec.yaml specifies FFI plugins as follows:

  plugin:
    platforms:
      some_platform:
        ffiPlugin: true

This configuration invokes the native build for the various target platforms and bundles the binaries in Flutter applications using these FFI plugins.

This can be combined with dartPluginClass, such as when FFI is used for the implementation of one platform in a federated plugin:

  plugin:
    implements: some_other_plugin
    platforms:
      some_platform:
        dartPluginClass: SomeClass
        ffiPlugin: true

A plugin can have both FFI and method channels:

  plugin:
    platforms:
      some_platform:
        pluginClass: SomeName
        ffiPlugin: true

The native build systems that are invoked by FFI (and method channel) plugins are:

  • For Android: Gradle, which invokes the Android NDK for native builds.
    • See the documentation in android/build.gradle.
  • For iOS and MacOS: Xcode, via CocoaPods.
    • See the documentation in ios/gonmea_flutter.podspec.
    • See the documentation in macos/gonmea_flutter.podspec.
  • For Linux and Windows: CMake.
    • See the documentation in linux/CMakeLists.txt.
    • See the documentation in windows/CMakeLists.txt.

Binding to native code

To use the native code, bindings in Dart are needed. To avoid writing these by hand, they are generated from the header file (src/gonmea_flutter.h) by package:ffigen. Regenerate the bindings by running flutter pub run ffigen --config ffigen.yaml.

Invoking native code

Very short-running native functions can be directly invoked from any isolate. For example, see sum in lib/gonmea_flutter.dart.

Longer-running functions should be invoked on a helper isolate to avoid dropping frames in Flutter applications. For example, see sumAsync in lib/gonmea_flutter.dart.

Flutter help

For help getting started with Flutter, view our online documentation, which offers tutorials, samples, guidance on mobile development, and a full API reference.