flutter json decode and file append not working on second run - json

Question

I was wondering if someone could help? I'm trying to load a file with json content, decode it, convert to a model/object add another element.
The way I'm trying to do this is as follows:
Flow 1: Check file exists = true -> return file object -> decode string to json -> convert to model/object -> add element -> back to json -> to string -> save file.
Flow 2: Check file exists = false -> create file -> add a json template -> return file object -> decode string to json -> convert to model/object -> add element -> back to json -> to string -> save file.
This is working on the first run (flow 1), it'll create the file, add the template then add the first new element. However, when I run it a second time (flow 2), I always get an throwback.
As we speak with the code below, the error is:
E/flutter (13140): [ERROR:flutter/runtime/dart_vm_initializer.cc(41)] Unhandled Exception: type 'List<dynamic>' is not a subtype of type 'Map<dynamic, dynamic>'
E/flutter (13140): #0 FileController.writeSingleResponseToFile (package:reefcommander/controllers/FileController.dart:33:39)
E/flutter (13140): <asynchronous suspension>
E/flutter (13140):
This is the code I'm using.
FileController.dart
import 'package:path_provider/path_provider.dart';
import 'dart:io';
import 'package:intl/intl.dart';
import 'package:reefcommander/models/ReadingsData.dart';
import 'package:reefcommander/models/SingleDataReqResponse.dart';
import 'dart:convert';
class FileController {
static String date = DateFormat("dd-MM-yyyy").format(DateTime.now());
static String template =
'{"name": "_NAME_", "friendlyName": "_FNAME_", "results": []}';
static final Map<String, String> nameDefenitions = {
'ec': 'EC',
'ph': 'pH',
'atoDayRate': 'Evap Rate',
'sumpTemp': 'Temp (sump)',
'tankTemp': 'Temp (tank)'
};
static Future<File> checkFileExists(String type) async {
readFile(type);
final Directory? directory = Platform.isAndroid
? await getExternalStorageDirectory() //FOR ANDROID
: await getApplicationSupportDirectory();
final String filename = '${directory!.path}/${date}_$type.json';
final File file = File(filename);
return file;
}
static writeSingleResponseToFile(SingleDataReqResponse resp) async {
final File file = await checkFileExists(resp.name.toString());
var r = Map<String, dynamic>.from(jsonDecode(await file.readAsString()));
print(r.runtimeType);
ReadingsData existingdata = ReadingsData.fromJson(r[0]);
//ReadingsData existingdata =
// r.map<ReadingsData>((json) => ReadingsData.fromJson(json));
print(existingdata);
existingdata.results!.add(Results(stamp: resp.stamp, value: resp.value));
print('DATA: ${existingdata.toJson().toString()}');
file.writeAsString(jsonEncode(existingdata.toJson().toString()));
}
static Future<void> deleteFile(String type) async {
try {
final Directory? directory = Platform.isAndroid
? await getExternalStorageDirectory() //FOR ANDROID
: await getApplicationSupportDirectory();
final String filename = '${directory!.path}/${date}_$type.json';
final File file = File(filename);
if (file.existsSync()) {
await file.delete();
} else {}
} catch (e) {
// Error in getting access to the file.
}
}
static Future<String> readFile(String type) async {
String text = '';
try {
final Directory? directory = Platform.isAndroid
? await getExternalStorageDirectory() //FOR ANDROID
: await getApplicationSupportDirectory();
final String filename = '${directory!.path}/${date}_$type.json';
final File file = File(filename);
if (file.existsSync()) {
text = await file.readAsString();
} else {
file.create(recursive: true);
String tempbase = template;
String write = tempbase
.replaceAll('_NAME_', type.toString())
.replaceAll('_FNAME_', nameDefenitions[type]!);
await file.writeAsString(write);
text = await file.readAsString();
}
} catch (e) {
print("Read error");
}
return text;
}
}
ReadingsData.dart
import 'dart:convert';
class ReadingsData {
String? name;
String? friendlyName;
List<Results>? results;
ReadingsData(
{required this.name, required this.friendlyName, required this.results});
ReadingsData.fromJson(Map<String, dynamic> json) {
name = json['name'];
friendlyName = json['friendlyName'];
if (json['results'] != null) {
results = <Results>[];
json['results'].forEach((v) {
results!.add(Results.fromJson(v));
});
}
}
Map<String, dynamic> toJson() {
final Map<String, dynamic> data = <String, dynamic>{};
data['name'] = name;
data['friendlyName'] = friendlyName;
if (results != null) {
data['results'] = results!.map((v) => v.toJson()).toList();
}
return data;
}
}
class Results {
String? stamp;
String? value;
Results({required this.stamp, required this.value});
Results.fromJson(Map<String, dynamic> json) {
stamp = json['stamp'];
value = json['value'];
}
Map<String, dynamic> toJson() {
final Map<String, dynamic> data = <String, dynamic>{};
data['stamp'] = stamp;
data['value'] = value;
return data;
}
}
Test code
FileController.writeSingleResponseToFile(
SingleDataReqResponse(name: "test", stamp: "10:22:00", value: "2222"));

Answer 1

For anyone else in my situation, I've resolved it. Solution below.
static writeSingleResponseToFile(SingleDataReqResponse resp) async {
final File file = await checkFileExists(resp.name.toString());
ReadingsData existingdata =
ReadingsData.fromJson(jsonDecode(await file.readAsString()));
existingdata.results!.add(Results(stamp: resp.stamp, value: resp.value));
file.writeAsString(jsonEncode(existingdata.toJson()));
}