Use OpenApi in Flutter

UseOpenApiInFlutter.md

To generate an API client in Dart from an OpenApi.json file, and use it in Flutter, follow these steps:

Related: see this gist for how to generate an OpenApi.json file on build from an ASP.NET 8 Minimal API project

1. Create a new Flutter 3.10 (or later) Application project in Visual Studio Code: steps
2. Add the openapi_generator package to your project. Follow below steps instead of the instructions at pub.dev (at the time of writing they were out of date):
   • Include openapi_generator_annotationsin the dependencies section of your pubspec.yaml file :

     dependencies:
       openapi_generator_annotations: ^4.10.0

   • Include build_runner and openapi_generator in the dev_dependencies section of your pubspec.yaml file:

     dev_dependencies:
        build_runner:
        openapi_generator: ^4.10.0

   • Annotate a dart class with the @Openapi() annotation; specify the path to your OpenApi json file in the inputSpecFile parameter (note that paths are relative to the project root folder):

     import 'package:openapi_generator_annotations/openapi_generator_annotations.dart';
     
     @Openapi(
         additionalProperties:
         AdditionalProperties(pubName: 'example_api', pubAuthor: 'Your_Name'),
         inputSpecFile: '../Api/bin/Debug/net8.0/openapi.json',
         generatorName: Generator.dart,
         outputDirectory: 'apiclient')
     class Example extends OpenapiGeneratorConfig {}

   • Run this command to generate the OpenApi client from the json file that you specified in the annotation:
     dart run build_runner build --delete-conflicting-outputs
3. To use the generated client in your project, follow the instructions in the generated README.md (in the folder you specified in the @Openapi() outputDirectory parameter).
   Note that the instructions include:
   • how to add the generated package from your local disk as a dependency in your project, e.g.:

     dependencies:
       example_api:
         path: apiclient

   • a dart code snippet that shows the generated class name and a method call specifically for your API. You can use the class and method names from the README, but you need to add a base URL and a missing await, e.g. like this:

     import 'package:example_api/api.dart';
     
     final api_instance = AspNet8CoreAPIVersion1000CultureneutralPublicKeyTokennullApi(ApiClient(basePath: 'http://localhost:5139'));
     
     try {
         final result = await api_instance.todosGet();
         print(result);
     } catch (e) {
         print('Exception when calling AspNet8CoreAPIVersion1000CultureneutralPublicKeyTokennullApi->todosGet: $e\n');
     }