When specifying MainAxisAligment as key value in json i get null value

Question

I have a use case where i need to specify the aligment of certain images with json object

This is the json object where i specify the aligment:

# json_object.json  

{
  "aligment" : "center"
}

I also have a method in another file where i grab this json object:

# get_json_object.dart

class GetJsonObject{
  Future<Map<String, dynamic>> getJson() async {
    String jsonData =
        await rootBundle.loadString('assets/json_object.json');
    Map<String, dynamic> data = jsonDecode(jsonData);
    return data;
  }


}

I also have a another method where i do if else statement to specify which key ther is in key aligment from the json object. I first grab the mapped json from GetJsonObject().getJson() and then return the MainAxisAlignment based on the key value from key alignment.:

# get_alignment.dart

class GetAlignment {
   Future getAxisAlignment(String key) async {
    var mappedJson = await GetJsonObject().getJson();

    if (mappedJson[key] == mappedJson["start"]) {
      return MainAxisAlignment.start;
    } else if (mappedJson[key] == mappedJson["center"]) {
      return MainAxisAlignment.center;
    } else if (mappedJson[key] == mappedJson["end"]) {
      return MainAxisAlignment.end;
    }
  }
}

For the view i have stateful widget where i grab the return type MainAxisAlignment from GetAlignment().getAxisAlignment() from the file get_alignment.dart and use setState to set the return type from GetAlignment().getAxisAlignment() to the field axisAlignment. I then use field axisAlignment for the position of the FlutterLogo() with Row():

# test_view.dart


class TestView extends StatefulWidget {
  const TestView({Key? key}) : super(key: key);

  @override
  State<TestView> createState() => _TestViewState();
}

class _TestViewState extends State<TestView> {
  late MainAxisAlignment axisAlignment = MainAxisAlignment.start;


  setAlignment() async {
    final alignment =
    await GetAligmnent().getAlignment("alignment");

    setState(() {
      axisAlignment = alignment;
      
    });
  }

  @override
  initState() {
    setAlignment();
    super.initState();
  }


  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(),
      body: Center(
        child: Row(
          mainAxisAlignment: axisAlignment,
          children: [
            FlutterLogo()
          ],
        ),
      )
    );
  }
}

But for some reason i get error in setState(): E/flutter ( 9246): [ERROR:flutter/lib/ui/ui_dart_state.cc(209)] Unhandled Exception: type 'Null' is not a subtype of type 'MainAxisAlignment'

So the return type is Null value, but i don't understand why.

Answer 1

I found out why i got Null as return type from getAxisAlignment. The reason for this was that i used wrong format inside the if else. I had to change mappedJson["start"] to just plain String like this:

  Future getAlignment(String key) async {
    var settings = await clientSettings;

    if (settings[key] == "start") {
      return MainAxisAlignment.start;
    } else if (settings[key] == "center") {
      return MainAxisAlignment.center;
    } else if (settings[key] == "end") {
      return MainAxisAlignment.end;
    } else {
      return MainAxisAlignment.center;
    }
  }

And i added default return type to get rid of the error when the return type was Null