Generic deserialization in Flutter / Dart

2021-04-08 03:01 Deeko imported from Stackoverflow

I'm trying to write a HTTP driver class that takes in a generic class and deserializes the response. I haven't found a good, clean way to do this in Flutter.

I've defined datamodel classes like this:

class MyClass {
  String field1;
  String field2;
  
  MyClass.fromJson(Map<dynamic, dynamic> json) 
    : field1 = json["field1"],
      field2 = json["field2"];
}

This works well and good if I do it manually...

MyClass makeRequest() {
   Response response = http.get(url);
   MyClass class = MyClass.fromJson(jsonDecode(response.body));
   return class;
}

What I want, is to make a generic HTTP driver like this:

void makeRequest<T>() {
   Response response = http.get(url);
   T parsed = T.fromJson(jsonDecode(response.body));
   return parsed;
}

Is there a way to do this in Flutter/Dart? I've been trying to figure out the right syntax to use a base class and extends but haven't gotten it. Any ideas?

1 answer

answered 2021-04-08 04:02 Bach

This is what I usually use in my network call, feel free to use. Btw, I recommend the dio package for convenient headers and params config, as well as other error handling features.

// Define an extension
extension BaseModel on Type {
  fromJson(Map<String, dynamic> data) {}
}

// For single object
Future<T> makeGetRequest<T>({String url, Map<String, dynamic> params}) {
  return http
      .get(buildUrl(url, params)) // Don't need the buildUrl() if you use Dio
      .then((response) => handleJsonResponse(response))
      .then((data) => T.fromJson(data));

// For list of object
Future<List<T>> makeGetRequestForList<T>({String url, Map<String, dynamic> params}) {
  return http
      .get(buildUrl(url, params)) // Don't need the buildUrl() if you use Dio
      .then((response) => handleJsonResponse(response))
      .then((data) => List<T>.from(data.map((item) => T.fromJson(item)));
}

// Helper classes without Dio
String buildUrl(String url, [Map parameters]) {
  final stringBuilder = StringBuffer(url);
  if (parameters?.isNotEmpty == true) {
    stringBuilder.write('?');
    parameters.forEach((key, value) => stringBuilder.write('$key=$value&'));
  }
  final result = stringBuilder.toString();
  print(result);
  return result;
}

// With Dio, you can simply do this:
final res = await API().dio
      .get(url, queryParameters: params) // Don't need the [buildUrl] here      
      .then((response) => handleJsonResponse(response))
      .then((data) => T.fromJson(data));

// Handle JSON response
handleJsonResponse(http.Response response, [String endpoint = '']) {
  print(
      'API: $endpoint \nCODE: ${response.statusCode} \nBODY: ${response.body}');
  if (_okStatus.contains(response.statusCode)) {
    return jsonDecode(response.body);
  }
  if (response.statusCode == HttpStatus.unauthorized) {
    throw Exception(response.statusCode);
  } else {
    throw Exception("HTTP: ${response.statusCode} ${response.body}");
  }
}

Usage:

// Example class
class Post {
  final String title;

  Post({this.title});

  @override
  Post.fromJson(Map<String, dynamic> data) : title = data['title'];
}

// Use the function
Future<Post> getPost() async {
  final result = await makeGetRequest<Post>(params: {'post_id': 1});
  return result;
}

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How can I get seperately the values from both drop-down Menus and send them to Firebase ?

Flutter: disabling textfields based on toggle button and ignoring their textfield texteditingcontroller requirements

I am trying to have my the title of my toggle buttons cause different calculations to be preformed. I also have the visibility of some textfields based on the selection of the toggle buttons. However, I can not get my app to run without providing actual values in each textfield. Is there a way to prevent this requirement? i.e. I don't need to provide values for the percent removed, flow rate, and the SCr but instead only provide one of those.

import 'package:pocketpk/models/calculator_vanc.dart';
import 'package:pocketpk/screens/vancomycin/vanc_results_screen.dart';
import 'package:pocketpk/widgets/input_row.dart';
import 'package:pocketpk/widgets/my_unit.dart';
import 'package:pocketpk/widgets/my_button.dart';
import 'package:pocketpk/widgets/make_buttons.dart';
import 'package:pocketpk/constants.dart';
import 'package:pocketpk/widgets/rounded_button.dart';
import 'package:auto_size_text/auto_size_text.dart';
import 'dart:math';

class VancDosingScreen extends StatefulWidget {
  static const String id = 'vancomycin dosing screen';
  @override
  _VancDosingScreenState createState() => _VancDosingScreenState();
}

class _VancDosingScreenState extends State<VancDosingScreen> {
  final MyButton genderSelected = MyButton();
  final MyButton renalReplacementTherapy = MyButton();
  final TextEditingController weightController = TextEditingController();
  final TextEditingController heightController = TextEditingController();
  final TextEditingController creatController = TextEditingController();
  final TextEditingController ageController = TextEditingController();
  final TextEditingController hDController = TextEditingController();
  final TextEditingController flowRateController = TextEditingController();
  final MyUnit heightUnit = MyUnit();
  final MyUnit weightUnit = MyUnit(imperial: 'lbs', metric: 'kg');
  final MyUnit creatUnit = MyUnit(imperial: 'mg/dL', metric: 'mg/dL');
  final MyUnit ageUnit = MyUnit(imperial: 'years', metric: 'years');
  final MyUnit hDUnit = MyUnit(imperial: '%', metric: '%');
  final MyUnit flowRateUnit = MyUnit(imperial: 'mL/hr', metric: 'L/hr');

  List<bool> isSelected = [
    false,
    false,
  ];

  List<bool> rRTIsSelected = [false, false, false];
  String buttonName = 'didntWork';
  String rRTButtonName = 'didntWork';

  @override
  Widget build(BuildContext context) {
    return Scaffold(
        backgroundColor: Colors.white,
        body: Column(children: <Widget>[
          ClipPath(
            clipper: MyClipper(),
            child: Container(
              height: MediaQuery.of(context).size.height * 0.28,
              width: double.infinity,
              decoration: BoxDecoration(
                gradient: LinearGradient(
                  begin: Alignment.topRight,
                  end: Alignment.bottomLeft,
                  colors: [
                    Color(0xff3383CD),
                    Color(0xff11249F),
                  ],
                ),
                image: DecorationImage(
                  image: AssetImage('images/equations1.png'),
                  fit: BoxFit.fill,
                ),
              ),
              child: Column(
                crossAxisAlignment: CrossAxisAlignment.center,
                mainAxisAlignment: MainAxisAlignment.center,
                children: <Widget>[
                  Padding(padding: EdgeInsets.all(20)),
                  AppBar(
                    leading: null,
                    actions: <Widget>[
                      IconButton(
                          icon: Icon(Icons.close),
                          onPressed: () {
                            Navigator.pop(context);
                          }),
                    ],
                    title: Text('Vancomycin'),
                    backgroundColor: Colors.transparent,
                    elevation: 0.0,
                  ),
                ],
              ),
            ),
          ),
          Container(
            width: MediaQuery.of(context).size.width * 0.9,
            child: Row(
              mainAxisAlignment: MainAxisAlignment.spaceBetween,
              children: <Widget>[
                Text(
                  'Gender',
                  style: TextStyle(
                    color: Colors.black,
                    fontSize: 20,
                  ),
                ),
                ValueListenableBuilder<Option>(
                  valueListenable: genderSelected,
                  builder: (context, option, _) => MakeButtons(
                    num0: 3,
                    num1: 5,
                    makeButtonWidth: MediaQuery.of(context).size.width * 0.20,
                    selected: option,
                    onChanged: (newOption) => genderSelected.option = newOption,
                  ),
                ),
              ],
            ),
          ),
          InputRow(
            myUnit: heightUnit,
            inputParameter: 'height',
            textField: heightController,
            colour: kEmoryDBlue,
          ),
          InputRow(
            myUnit: weightUnit,
            inputParameter: 'weight',
            textField: weightController,
            colour: kEmoryDBlue,
          ),
          InputRow(
            myUnit: ageUnit,
            inputParameter: 'Age',
            textField: ageController,
            colour: kEmoryDBlue,
          ),
          Container(
            width: MediaQuery.of(context).size.width * 0.9,
            child: Row(
              mainAxisAlignment: MainAxisAlignment.spaceBetween,
              children: <Widget>[
                AutoSizeText(
                  'Renal Replacement Therapy',
                  style: TextStyle(
                    color: Colors.black,
                  ),
                ),
                ToggleButtons(
                  color: kEmoryDBlue,
                  selectedColor: Colors.white,
                  fillColor: kEmoryDBlue,
                  children: <Widget>[
                    Container(
                      padding: EdgeInsets.fromLTRB(12, 12, 12, 12),
                      constraints:
                          BoxConstraints.expand(width: 100, height: 56),
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                        child: Text(
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                          style: TextStyle(
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                        ),
                      ),
                    ),
                    Container(
                      padding: EdgeInsets.fromLTRB(12, 12, 12, 12),
                      constraints:
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                      child: Center(
                        child: Text(
                          'No',
                          style: TextStyle(
                              fontSize: 20, fontWeight: FontWeight.w500),
                        ),
                      ),
                    ),
                  ],
                  isSelected: isSelected,
                  onPressed: (int index) {
                    setState(() {
                      for (int indexBtn = 0;
                          indexBtn < isSelected.length;
                          indexBtn++) {
                        if (indexBtn == index) {
                          isSelected[indexBtn] = !isSelected[indexBtn];
                        } else {
                          isSelected[indexBtn] = false;
                        }
                      }
                      buttonName =
                          isSelected[index] == isSelected[0] ? 'Yes' : 'No';
                    });
                  },
                ),
              ],
            ),
          ),
          Visibility(
            visible: isSelected[0],
            child: Container(
              width: MediaQuery.of(context).size.width * 0.9,
              child: Center(
                child: ToggleButtons(
                  color: kEmoryDBlue,
                  selectedColor: Colors.white,
                  fillColor: kEmoryDBlue,
                  children: <Widget>[
                    Container(
                      padding: EdgeInsets.fromLTRB(12, 12, 12, 12),
                      constraints:
                          BoxConstraints.expand(width: 125, height: 56),
                      child: Center(
                        child: Text(
                          'HD',
                          style: TextStyle(
                              fontSize: 20, fontWeight: FontWeight.w500),
                        ),
                      ),
                    ),
                    Container(
                      padding: EdgeInsets.fromLTRB(12, 12, 12, 12),
                      constraints:
                          BoxConstraints.expand(width: 125, height: 56),
                      child: Center(
                        child: Text(
                          'CRRT',
                          style: TextStyle(
                              fontSize: 20, fontWeight: FontWeight.w500),
                        ),
                      ),
                    ),
                    Container(
                      padding: EdgeInsets.fromLTRB(12, 12, 12, 12),
                      constraints:
                          BoxConstraints.expand(width: 125, height: 56),
                      child: Center(
                        child: Text(
                          'PD',
                          style: TextStyle(
                              fontSize: 20, fontWeight: FontWeight.w500),
                        ),
                      ),
                    ),
                  ],
                  isSelected: rRTIsSelected,
                  onPressed: (int index) {
                    setState(() {
                      for (int indexBtn = 0;
                          indexBtn < rRTIsSelected.length;
                          indexBtn++) {
                        if (indexBtn == index) {
                          rRTIsSelected[indexBtn] = !rRTIsSelected[indexBtn];
                        } else {
                          rRTIsSelected[indexBtn] = false;
                        }
                      }
                      if (rRTIsSelected[index] == rRTIsSelected[0] &&
                          isSelected[0]) {
                        return rRTButtonName = 'HD';
                      } else if (rRTIsSelected[index] == rRTIsSelected[1] &&
                          isSelected[0]) {
                        return rRTButtonName = 'CRRT';
                      } else if (isSelected[0]) {
                        return rRTButtonName = 'PD';
                      } else {
                        return rRTButtonName = 'X';
                      }
                    });
                  },
                ),
              ),
            ),
          ),
          Visibility(
            visible: rRTIsSelected[0] & isSelected[0],
            child: InputRow(
              myUnit: hDUnit,
              enable: rRTButtonName == 'HD' ? true : false,
              inputParameter: 'Estimated Percent Removed by Dialysis',
              textField: hDController,
              colour: kEmoryDBlue,
            ),
          ),
          Visibility(
            visible: rRTIsSelected[1] & isSelected[0],
            child: InputRow(
              myUnit: flowRateUnit,
              enable: rRTButtonName == 'CRRT' ? true : false,
              inputParameter: 'Flow rate',
              textField: flowRateController,
              colour: kEmoryDBlue,
            ),
          ),
          Visibility(
            visible: isSelected[1],
            child: InputRow(
              myUnit: creatUnit,
              enable: buttonName == 'No' ? true : false,
              inputParameter: 'SCr',
              textField: creatController,
              colour: kEmoryDBlue,
            ),
          ),
          RoundedButton(
              title: 'Calculate',
              onPressed: () {
                double weightSelected;
                double height = heightUnit == 'cm'
                    ? double.parse(heightController.text)
                    : double.parse(heightController.text) * 2.54;
                double weight = weightUnit == 'kg'
                    ? double.parse(weightController.text)
                    : double.parse(weightController.text) / 2.2;
                double ideal = genderSelected.title == 'Female'
                    ? 45 + 2.3 * ((height - 152.4) / 2.54)
                    : 50 + 2.3 * ((height - 152.4) / 2.54);
                double adjust = (weight - ideal) * 0.4 + ideal;

                if (weight > 1.3 * ideal) {
                  weightSelected = adjust;
                } else if (ideal > weight) {
                  weightSelected = weight;
                } else {
                  weightSelected = ideal;
                }

                double isFemale =
                    genderSelected.title == 'Female' ? 0.85 : 1.00;

                double crcl = (((140 - double.parse(ageController.text)) *
                            weightSelected) /
                        (72 * double.parse(creatController.text))) *
                    isFemale;

                double percentRemoved = double.parse(hDController.text);

                double flowRate = flowRateUnit == 'L/hr'
                    ? double.parse(flowRateController.text) * 1000
                    : double.parse(flowRateController.text);

                double ke = 0.00083 * crcl + 0.0044;
                double tau = (log(35 / 17.5) / ke + 1);

                double buttonsPushed;
                double updateRoundedTau;

                double roundedTau() {
                  if (tau < 7) {
                    return 6;
                  } else if (tau < 10) {
                    return 8;
                  } else if (tau < 15) {
                    return 12;
                  } else if (tau < 20) {
                    return 18;
                  } else if (tau < 30) {
                    return 24;
                  } else if (tau < 40) {
                    return 36;
                  } else if (tau < 55) {
                    return 48;
                  } else {
                    return 72;
                  }
                }

                if (isSelected[1]) {
                  buttonsPushed = 0;
                  updateRoundedTau = roundedTau();
                  flowRate = 0;
                  percentRemoved = 0;
                } else if (isSelected[0] && rRTIsSelected[0]) {
                  buttonsPushed = 10;
                  percentRemoved;
                  flowRate = 0;
                  crcl = 0;
                  ke = 0;
                  tau = 0;
                  updateRoundedTau = 0;
                } else if (isSelected[0] && rRTIsSelected[1]) {
                  buttonsPushed = 11;
                  percentRemoved = 0;
                  crcl = 0;
                  ke = 0;
                  tau = 0;
                  if (flowRate < 3000) {
                    updateRoundedTau = 24;
                  } else if (flowRate < 4000) {
                    updateRoundedTau = 18;
                  } else {
                    updateRoundedTau = 12;
                  }
                } else {
                  buttonsPushed = 12;
                  flowRate = 0;
                  crcl = 0;
                  ke = 0;
                  tau = 0;
                  updateRoundedTau = 0;
                  percentRemoved = 0;
                }

                print(percentRemoved);
                print(flowRate);

                CalculatorVancDosing vancCalc;
                vancCalc = CalculatorVancDosing(
                  button: buttonsPushed,
                  weight: weightSelected,
                  tau: updateRoundedTau,
                  percent: percentRemoved,
                  flow: flowRate,
                  ke: ke,
                );

                Navigator.push(
                  context,
                  MaterialPageRoute(
                    builder: (context) => VancResultsScreen(
                      vancTau: vancCalc.calculateTau(),
                      vancDosingLoad: vancCalc.calculateLoadDose(),
                      vancDosingMaint: vancCalc.calculateMaintDose(),
                      screenLayout: 2,
                    ),
                  ),
                );
              })
        ]));
  }
}

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I can't work out why this is happening.

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                                      postDetails: _postDetailsController.text,
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                          ),
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                    ),
                  ),
                );
              });
        },
      ),
    ),
  );
}

Items not being added to list using .Add()
I have a class named Model which contains a property Elements. Upon the deserialization of a json, I wish to add the newly resulted object to the list of Elements - however, it does not get added.

Firstly, my Model.cs:
```
public class Model
{
  public new IEnumerable<Element> Elements { get; }
  public new IEnumerable<Connection> Connections { get; }
}
```
Please note that there are no setters, and I can not add them. This class should remain as it is.

Next, the deserialization and my attempt to add the Elements to the newly created model.
```
Model newModel = new Model();

foreach (var item in jsonResponse) {
   JArray jElements = (JArray) item.Value;
   foreach (var rItem in jElements) {
      JObject rItemValueJson = (JObject) rItem;
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      newModel.Elements.ToList().Add(rowsResult);
   }
}
```
I can not instantiate a new list like below: newModel.Elements = new List<MEP.Calculations.Common.Models.Element>();

or assign the rowsResult because:

Property or indexer 'Model.Elements' cannot be assigned to -- it is read only The property Model.Elements has no setter

Is there any possible workaround for this, except for, as I previously mentioned, adding a setter?
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Assuming this java class :
```
public class Status {
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    private String name;
    private Point position;
}
```
With Point position being the object from java.awt.Point (a java core package class), you can serialize it producing this schema :
```
{
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  "name": "Status",
  "namespace": "com.example.entities",
  "fields": [
    {
      "name": "id",
      "type": "long"
    },
    {
      "name": "name",
      "type": "string"
    },
    {
      "name": "position",
      "type": {
        "type": "record",
        "name": "Point",
        "namespace": "java.awt",
        "fields": []
      }
    }
  ]
}
```
However, when deserializing this schema to generate classes (using the avro-maven-plugin), I end up with :
- The Status class (seems ok)
- The java.awt.Point in a new Package, generated with Avro. It is this one that is referenced in the Status class
The Point package does not include any fields that the core package contains (ie. double x and double y).

A few questions :
- Is there a way to exclude java core package from Avro class generation ? (I want to use the original package, not a generated one)
- If not, how do you assign the Point fields in the Status generated class ? (put(String field, Object value) ?)
Edit : Note that it behaves similarly with java.awt.Polygon and java.sql.Timestamp (and I'm sure other classes from java core package would too)
MissingMethodException Json.Serializer Constructor on type not found exception in WASM unoplatform
I am using System.Text.Json.JsonSerializer.Deserialize to deserialize string into my class.

Here is my class:
```
namespace Database
{
    public class Song
    {
        public uint id { get; set; }

        public string name { get; set; }

        public string author { get; set; }

        public int bpm { get; set; }
    }
}
```
Here is code of deserialization with jsonData being [{"id":1,"name":"1","author":"1","bpm":0},{"id":2,"name":"2","author":"2","bpm":0}]
```
List<Song> songs = JsonSerializer.Deserialize<List<Song>>(jsonData);
```
It works perfectly fine on UWP and Android projects in Uno-Platform. However, on WASM exception MissingMethodException is thrown. Here is the log:
```
System.MissingMethodException: Constructor on type 'System.Text.Json.Serialization.Converters.ListOfTConverter`2[[System.Collections.Generic.List`1[[Database.Song, BP.Wasm, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null]], mscorlib, Version=2.0.5.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e],[Database.Song, BP.Wasm, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null]]' not found.
```
As far I understand the log. It doesn't know how to deserialize List<Song>. Neither the overview or any of the Additional resources says anything about some exceptions to what types are supported by de/serialization in what framework.

Do I have to define my own converters for List of Song and potentially other Collections? Could this be related to Uno Platform anyhow? Or am I just missing something trivial?

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