[Accessing API Endpoint] #api #flutter #dart

example_flutter_api.dart

//Syntax
class Api {
  final HttpClient _httpClient = HttpClient();
  final String _url = 'urltoaccess.com';
  
  //GET /$path/B
  Future<TypeToConvert> callType1(
        String path, String param1, String param2, String param3) async {
      final uri = Uri.https(_url, '/$path/B',
          {'param1': param1, 'param2': param2, 'param3': param3});
      final jsonResponse = await _getJson(uri);
      if (jsonResponse == null || jsonResponse['status'] == null) {
        print('Error retrieving conversion.');
        return null;
      } else if (jsonResponse['status'] == 'error') {
        print(jsonResponse['message']);
        return null;
      }
      return jsonResponse['params'];
  }
  
  //Helper Method to make network request
  Future<Map<String, dynamic>> _getJson(Uri uri) async {
      try {
        final httpRequest = await _httpClient.getUrl(uri);
        final httpResponse = await httpRequest.close();
        if (httpResponse.statusCode != HttpStatus.OK) {
          return null;
        }
        final responseBody = await httpResponse.transform(utf8.decoder).join();
        return json.decode(responseBody);
      } on Exception catch (e) {
        print('$e');
        return null;
      }
  }
}

//Example
class Api {
  final HttpClient _httpClient = HttpClient();

  final String _url = 'flutter.udacity.com';

  Future<List> getUnits(String category) async {
    final uri = Uri.https(_url, '/$category');
    final jsonResponse = await _getJson(uri);
    if (jsonResponse == null || jsonResponse['units'] == null) {
      print('Error retrieving units.');
      return null;
    }
    return jsonResponse['units'];
  }

  Future<double> convert(
      String category, String amount, String fromUnit, String toUnit) async {
    final uri = Uri.https(_url, '/$category/convert',
        {'amount': amount, 'from': fromUnit, 'to': toUnit});
    final jsonResponse = await _getJson(uri);
    if (jsonResponse == null || jsonResponse['status'] == null) {
      print('Error retrieving conversion.');
      return null;
    } else if (jsonResponse['status'] == 'error') {
      print(jsonResponse['message']);
      return null;
    }
    return jsonResponse['conversion'].toDouble();
  }

  Future<Map<String, dynamic>> _getJson(Uri uri) async {
    try {
      final httpRequest = await _httpClient.getUrl(uri);
      final httpResponse = await httpRequest.close();
      if (httpResponse.statusCode != HttpStatus.OK) {
        return null;
      }
      final responseBody = await httpResponse.transform(utf8.decoder).join();
      return json.decode(responseBody);
    } on Exception catch (e) {
      print('$e');
      return null;
    }
  }
}