Flutter/Dart - How to pass variables between classes? - json

Question

I am very new to programming and I am trying to pass a variable (jsonData) from a future to another future in a different class, so the data from the variable can be stored in a database. Dont be confused, I am using an API for getting the neccessary data, this works perfectly fine. Any tips how I can access the variable jsonData to insert the data?
//first class gets the json data
class getJSONData {
Future<void> makeRequest() async {
var url = "some url";
Map inputData = {
"Password": example,
"SQL": sql query,
"db_server": "server",
"db_table": "table",
};
var body = json.encode(inputData);
var putRequest = await http.put(
Uri.encodeFull(url), headers: {"Content-Type": "application/json"},
body: body);
//this variable has to be stored
var jsonData = json.decode(putRequest.body);
}
}
//data needs to be inserted here
class Database {
Future<void> insertJSON() async {
db = await openDatabase(
join(await getDatabasesPath(), tableName),
onCreate: (db, version) {
return db.execute('''
INSERT INTO $tableName(column1, column2, etc) VALUES (${jsonData["Records].data1}, ${jsonData["Records].data2}, etc)
''');
}
);
}
}

Answer 1

below i am showing you how to pass data between two screens :
Screen 1 :
class HomeScreenTopContainer extends StatefulWidget {
#override
_HomeScreenTopContainerState createState() => _HomeScreenTopContainerState();
}
class _HomeScreenTopContainerState extends State<HomeScreenTopContainer> {
#override
void initState() {
// TODO: implement initState
super.initState();
}
#override
Widget build(BuildContext context) {
return Stack(
children: <Widget>[
Inkwell(onTap:(){
Navigator.push(
context,
MaterialPageRoute(builder: (context) => ParentLanding(parameter:"pass your value here")),
);
},child:Text("Tap Here and pass data")),
],
);
}
}
Screen 2 :
class ParentLanding extends StatefulWidget {
String parameter;
ParentLanding({Key key,String parameter}) : super(key: key,parameter:parameter);
#override
_ParentLandingState createState() => _ParentLandingState();
}
class _ParentLandingState extends State<ParentLanding> {
#override
void initState() {
// TODO: implement initState
super.initState();
}
#override
Widget build(BuildContext context) {
return Stack(
children: <Widget>[
Inkwell(onTap:(){
// you can use this parameter like this.
},child:Text(**Widget.parameter**)),
],
);
}
}

Answer 2

You have many options.
I'll suggest you one.
Change the signatures of both methods.
Example
Your HttpClient class
Future<Map<String, dynamic>> makeRequest() async {
// ... your code
var jsonData = json.decode(putRequest.body);
return jsonData;
}
Your DB Class
Future<void> insertJSON(Map<String, dynamic> jsonData) async {
db = await openDatabase(
join(await getDatabasesPath(), tableName),
onCreate: (db, version) {
return db.execute('''
INSERT INTO $tableName(column1, column2, etc) VALUES
(${jsonData["Records].data1}, ${jsonData["Records].data2}, etc)
''');
}
);
}
Use a third Class/object/method that make the call to the api, take the result and pass it to the db class:
main() async {
HttClient http = HttpClient();
Database db = Database();
final json = await http.makeRequest();
await db.insertJSON(json);
}

Answer 3

Easiest way to pass any value is using an argument.
Value can be send as:
Keys.navKey.currentState.pushNamed(
Routes.gameViewScreen, arguments: jsonData );
In another class it can be retrieved as :
var jsonData = ModalRoute.of(context).settings.arguments;