So, I'm trying to do something that seems simple, but I can't get why it is not working.
I wrote this code:
class HomepageModel {
List<dynamic> data = [];
String _url = '[...]'; //My URL is working
Future _comm() async {
data = await httpFetch(_url); //This 'httpFetch' just does some json decoding
print(data); //Shows data normally
}
HomepageModel() {
_comm();
print(data); //Shows empty list
}
}
I want to store data retrieved from an API in the field data. I was able to get the data in function _comm, and when I print the field, it shows normally. But, outside this method, the content of the data field seems to have disappeared! Both on the print in the constructor, and in other files, all the prints show just an empty list.
What should I do to be able to properly store data from the API in a class field?
class HomepageModel {
List<dynamic> data = [];
String _url = '[...]'; //My URL is working
Future _comm() async {
data = await httpFetch(_url); //This 'httpFetch' just does some json decoding
print(data); //Shows data normally
}
HomepageModel() {
_comm().then((_){
print(data);
});
}
}
Related
Hi so i'm new to dart and I'm having an issue with returning 2 value from a dart function.
Currently I have this function :
Future LoadAllData({required Map data, required String detailId}) async {
loadUserData(data: data);
powData = await Database.getPowDataActive(detailId: detailId);
return powData;
}
so getPowDataActive is a function that will fetch a data from my database and it will return some map data, load user data will also fetch data and will also return some map. I wanted to use the loadAllData function for my futureBuilder and use the snapshot data from this 2 function for different purposes, can I do so ? or I have to first combine the return from both function into 1 variable and access it differently ?
Thanks before
You can create a model like this:
class LoadDataResult {
final Map userData;
final Map powData;
LoadDataResult({#requierd this.userData, #requierd this.powData, });
}
and then use it like this:
Future<LoadDataResult> LoadAllData({required Map data, required String detailId}) async {
var userData = await loadUserData(data: data);
powData = await Database.getPowDataActive(detailId: detailId);
return LoadDataResult(userData:userData, powData: powData);
}
and then use it like this in futureBuilder:
LoadDataResult data = snapshot.data;
print('${data. userData}');
I'm reading json List from device memory and want to perform some operations on it's components.
When I load that list I start loop where I check each item of that list.
While in loop I add each item to new List to have updated List after loop ends so I could save it on device memory.
If some conditions are true then I use future async http call to get updated data
then theoretically I update that item of the List while staying inside loop. And thus after loop ends I must have updated Json List ready to be saved on device memory.
Problem is that While I http call inside loop, the answer delays, loop ends and new Json List is being constructed and saved on memory without the component that was supposed to be updated.
Is there any way to force wait the whole loop or something else ?
Here is the code
Future<void> readStoredData() async {
try {
final prefs = await SharedPreferences.getInstance();
_rawJsonListE = prefs.getStringList('storedData');
List<String> rawJsonListNEW = [];
bool _isNeedUpdate = false;
_rawJsonListE!.forEach((item) async {
if (someCondition with item Data) {
_isNeedUpdate = true;
await makeHttpCallFutureAwaitFunction(item).then((_) {
rawJsonListNEW.add(updatedItem);
});
} else {
rawJsonListNEW.add(item);
}
});
if (_isNeedUpdate) prefs.setStringList('storedData', rawJsonListNEW);
}
notifyListeners();
} catch (error) {
print('Error : ${error}');
throw error;
}
You can separate the refreshing data part to another function.
// Just need to check _rawJsonListE is empty or not
_isNeedUpdate = _rawJsonListE.isNotEmpty();
Create a new function.
Future<List<String>> checkDataAndRefresh(List<String> _rawJsonListE) async {
List<String> rawJsonListNEW = [];
_rawJsonListE!.forEach((item) async {
if (someCondition with item Data) {
final String newString = await makeHttpCallFutureAwaitFunction(item);
rawJsonListNEW.add(newString);
} else {
rawJsonListNEW.add(item);
}
});
return rawJsonListNEW;
}
And if _isNeedUpdate is true, do work.
if (_isNeedUpdate)
final List<String> newData = await checkDataAndRefresh(_rawJsonListE);
prefs.setStringList('storedData', newData);
I'm a junior working with flutter and hit a problem.
I need to open a file, read and compare some data everytime the app opens and then change some of that data as the app progress. We tried using .txt files to read and write some text, but when we had to look for something in the file was too complicated to change it and the file is not accessibe only on the device running the app. We also thought of using xml files but I don't know if is a good idea.
What would be a pratical solution for this situation, as the file needs to be opened all the time. Thanks.
Let's say our JSON looks like this:
{
title: 'some text',
values: [1,5,2,4,1,3],
}
And we want to make a UI that allows us to add values and to edit the title. First let's write a method to write and read from the JSON file:
Future<void> _write(Map<String, dynamic> value) async {
File f = File(_fileLocation);
String jsonStr = jsonEncode(value);
await f.writeAsString(jsonStr);
}
Future<Map<String, dynamic>> _read() async {
File f = File(_fileLocation); // maybe move this into a getter
final jsonStr = await f.readAsString();
return jsonDecode(jsonStr) as Map<String, dynamic>;
}
This way, the rest of the app should be trivial, but let's add a method to update the title and a method to add a new number:
Future<void> _updateTitle(String title) async {
var values = await _read();
values['title'] = title;
await _write(values);
}
Future<void> _addNumber(int number) async {
var values = await _read();
values['values'].push(number);
await _write(values);
}
Types with JSON and Dart can be a bit weird, so it is possible you need to use the as keyword when reading from the list:
Future<void> _addNumber(int number) async {
var values = await _read();
var valueList = (values['values'] as List<int>);
valueList.push(number);
values['values'] = valueList;
await _write(values);
}
Hopefully, this example helps
class UserProvider extends ChangeNotifier {
UserLoginModel userLoginModel = UserLoginModel();
UserLoginModel get userdata {
return userLoginModel;
}
void addlogindata(UserLoginModel data) {
userLoginModel = data;
notifyListeners();
}
}
How to set data to this class using api or UserLoginModel through function
i want to set data like this
if (response.statusCode == 200) {
print(response.body);
var data = UserLoginModel.fromJson(jsonDecode(response.body)); userprovider.addlogindata(data);
bur i am getting error by doing this kind of thing
you can call the function like this within in the build method:
Provider.of<UserProvider>(context).addlogindata(data)
outside the build method:
Provider.of<UserProvider>(context,listen:false).addlogindata(data)
var data=Provider.of<UserProvider>(context,listen:false);
var newdata=data.addlogindata(responsedata);
that work perfectly for me and now i can use that data anywhere in the app
I've fetched a json object and deserialized it and then returned it too.
I want to use this in another file.
I'm unable to assign the values that I'm getting in the first step.
Here are all the codes...
Service
Future getGeoPoints(String accessToken, String tripId) async {
String requestUrl;
var response = await get(
Uri.parse(requestUrl),
headers: {
'Authorization': "Bearer $accessToken",
},
);
if (response.statusCode == 200) {
Map<String, dynamic> responseBody = json.decode(response.body);
GetGeoPoints geoPoints = GetGeoPoints.fromJson(responseBody);
List listOfGeoPoints = [];
for (var geoPoint in geoPoints.geoPoints) {
listOfGeoPoints.add(
{
'latitude': geoPoint.latitude,
'longitude': geoPoint.longitude,
'timestamp': geoPoint.timeStamp,
},
);
}
// print('List of geo points: ' + '$listOfGeoPoints');
return listOfGeoPoints;
} else {
throw Exception('Failed to load data from server');
}
}
File where I need the above values
List routeCoordinates;
Future<void> getValues() async {
getGeoPoints(widget.accessToken, widget.tripId)
.then((value) => routeCoordinates = value);
}
When I run the app, routeCoordinates is null but when I hotreload, it contains the value.
I want to have the values as soon as the screen starts. What is the right way to assign the values here?
I've also tried this:
routeCoordinates = getGeoPoints...
It throws error..
Please help.. Thanks..
The function getGeoPoints() is an asynchronous one. But on the other file, you are not using the await keyword, instead you are using then(). So your code is not waiting for that function to return value.
Try using below code,
List routeCoordinates;
Future<void> getValues() async {
routeCoordinates = await getGeoPoints(widget.accessToken, widget.tripId);
}
Let us know how it went.
You need to use a FutureBuilder to define a behaviour depending on the state of the request. You'll be able to tell the widget what to return while your app is waiting for the response to your request. You can also return a specific widget if you get an error(if your user is offline, for example).
Edit: I've linked the official docs but give this article a read if it's not clear enough.