I have a link.txt file that i want to display it's content on a text widget
I tried this approach
try {
HttpClient client = HttpClient();
client.getUrl(Uri.parse(arbitaryLink.txt)).then((HttpClientRequest request) {
return request.close();
}).then((HttpClientResponse response) {
response
.transform(Utf8Decoder())
.listen((contents) {
// Do something here with contents
return Text(contents);
});
});
} catch (exception) {
print(exception);
}
contents is the response text .. whenever i try using it outside of it's scope, i get null value.
i tried returning Text, i even tried assigning it to a static variable but i got nothing.
Soo.. What am i doing wrong?
This is how i solved
Future<String> _fetchBtaqa() async {
final response = await http.get('https://www.albetaqa.site/social/data/alwaraqa/02quran/1quran03/p-quran116.txt');
if (response.statusCode == 200) {
var decoded = utf8.decode(response.bodyBytes);
print(decoded);
return decoded;
} else {
return "Error";
}
}
If by outside its scope you mean that you are returning the value of the response and then trying to use it in some widget, then the case might be that you are not waiting for the client to fetch the response.
1) make sure the when you print contents in the scope you are getting a value
2) put the api call or the networking call in a function and add the await keyword to wait for the response.
3) When the response succeeds you can call setState to rebuild the widget with the new value of contents
Related
How do I set up a flutter method to return a future value that is drawn from the results of a future http post call inside the method?
The example code below is making a call to a web URL to add a new product. I want this method to return just the Id of the newly created product (i.e. 'name' inside response)
Future<String> add(Product aNewProduct) async {
var aUrl = Uri.parse(dbUrl);
http.post(aUrl,body: toBody(aNewProduct),).then((response) {
var aStr = json.decode(response.body)['name'];
return Future<String>.value(aStr);
});
}
With the code above, the parser is showing the following error/warning...
The body might complete normally, causing 'null' to be returned,
but the return type, 'FutureOr<String>', is a potentially non-nullable type.
(Documentation) Try adding either a return or a throw statement at the end.
Any suggestions on how to fix this?
You can use the await to get the value of a Future or rather your http request. After that you can simple decode it and return your desired behavior.
Future<String> add(Product aNewProduct) async {
var aUrl = Uri.parse(dbUrl);
final response = http.post(
aUrl,
body: toBody(aNewProduct),
);
return json.decode(response.body)['name'];
}
try this:
Future<String> add(Product aNewProduct) async {
var aUrl = Uri.parse(dbUrl);
var response= await http.post(aUrl,body: toBody(aNewProduct),);
if(response.statusCode==200){
var rawData = await response.stream.bytesToString();
Map data=json.decode(rawData);
return data['name'];
}else{
return '';
}
}
It is as simple as putting a return before the http.post statement
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.
I have below code in flutter:
getData() {
final linksStream = getLinksStream().listen((String uri) async {
return uri;
});
}
In getData method, I want to return the value of uri which is from a stream listener. Since this value is generated at a later time, I am thinking to response a Future object in getData method. But I don't know how I can pass the uri as the value of Future.
In javascript, I can simply create a promise and resolve the value uri. How can I achieve it in dart?
In your code 'return uri' is not returning from getData but returning from anonymous function which is parameter of listen.
Correct code is like:
Future<String> getData() {
final Completer<String> c = new Completer<String>();
final linksStream = getLinksStream().listen((String uri) {
c.complete(uri);
});
return c.future;
}
Try this
Future<String> getData() async{
final linksStream = await getLinksStream().toList();
return linksStream[0].toString();
}
getData() async {
http.Response response = await http.get('https://www.example.com/);
print(response.body);
}
The above function works to get the HTML code of a page but it fails in some cases. The function is sometimes never completed and it waits forever to get response( For example, if the app is opened while internet is off and even when its turned on, it never connects). In such situations is there any way to retry ?
I tried the http retry package but it gives me 15+ errors.
Example code for how this could be done:
import 'package:http/http.dart' as http;
import 'dart:convert';
Future<List> loadData() async {
bool loadRemoteDatatSucceed = false;
var data;
try {
http.Response response = await http.post("https://www.example.com",
body: <String, String>{"username": "test"});
data = json.decode(response.body);
if (data.containsKey("success")) {
loadRemoteDatatSucceed = true;
}
} catch (e) {
if (loadRemoteDatatSucceed == false) retryFuture(loadData, 2000);
}
return data;
}
retryFuture(future, delay) {
Future.delayed(Duration(milliseconds: delay), () {
future();
});
}
You can use RetryPolicy from http package to retry your connection, just create your own class and inherit form RetryPolicy and override these function like the following example, then create a Client using HttpClientWithInterceptor.build and add your custom retryPolicy as a parameter, this will retry your request for a number of times until a condition is met, if not, it'll just stop retrying.
import 'package:http/http.dart';
class MyRetryPolicy extends RetryPolicy {
final url = 'https://www.example.com/';
#override
// how many times you want to retry your request.
int maxRetryAttempts = 5;
#override
Future<bool> shouldAttemptRetryOnResponse(ResponseData response) async {
//You can check if you got your response after certain timeout,
//or if you want to retry your request based on the status code,
//usually this is used for refreshing your expired token but you can check for what ever you want
//your should write a condition here so it won't execute this code on every request
//for example if(response == null)
// a very basic solution is that you can check
// for internet connection, for example
try {
final result = await InternetAddress.lookup('google.com');
if (result.isNotEmpty && result[0].rawAddress.isNotEmpty) {
return true;
}
return false;
} on SocketException catch (_) {
return false;
}
}
}
then create and use a client to make your requests.
it will automatically retry the request if the condition you wrote is met.
Client client = HttpClientWithInterceptor.build(
retryPolicy: ExpiredTokenRetryPolicy(),
);
final response = await client.get('https://www.example.com/);
there is also a package to check for internet connection if that your problem, see connectivity
You can use try-catch blocks inside async functions like you would in synchronous code. Perhaps you'd be able to add some sort of error handling mechanism in the function, and retry the function on error? Here's some documentation on that one.
Example from the docs:
try {
var order = await getUserOrder();
print('Awaiting user order...');
} catch (err) {
print('Caught error: $err');
}
You can also catch specific Exceptions, per this github issue.
doLogin(String username, String password) async {
try {
var user = await api.login(username, password);
_view.onLoginSuccess(user);
} on Exception catch(error) {
_view.onLoginError(error.toString());
}
}
EDIT: This may also help.
While we're at it, look here for a function that reattempts an async operation however many times you need.
I am trying to make a simple request to backend using rxDart. But the problem I face is that when I get a http error such as 404, onError is not called, however, it is possible to extract it in onData.
I have a little experience with RxJava + retrofit and there it works as expected, when there is a response with error http status code onError is called and can be handled appropriately.
1. What am I doing wrong, or is it intended behavior?.
Object sendProfileData() {
Stream<Response> stream = onboardingRepository.createUser(User(name: 'name', surname: 'surname', lat: 1.0, lng: 2.0));
stream.listen((response) {
print(response.statusCode);
setAttributes();
}, onError: (e) {
print(e);
});
}
OnboardingRepository.dart:
class OnboardingRepository {
Observable<Response> createUser(User user) {
return Observable.fromFuture(TMApi.createUser(user));
}
}
TMApi.dart:
class TMApi {
static Future<http.Response> createUser(User user) async {
String url = '$baseUrl/create_user';
return await http.post(url, body: json.encode(user.toJson()));
}
}
What would be the best way to handle the event in the View? There should be an error displayed if error occurs, otherwise it should open a new screen. sendProfileData() method will return an Object, based on that I am going to perform actions in the view, but that doesn't sound like a very elegant solution...
Any suggestions on architecture are welcome :)
the http library in dart works a bit different than Retrofit.
The Future returned by http.post only throws an exception when there is an io error (socket error, no internet).
Server responses like 404 are reflected in the http.Response.
I created a simple convenience method that might help you:
void throwIfNoSuccess(http.Response response) {
if(response.statusCode < 200 || response.statusCode > 299) {
print('http error!');
print(response.body);
throw new HttpException(response);
}
}
class HttpException implements Exception {
HttpException(this.response);
http.Response response;
}
How to use:
import 'dart:convert';
import 'package:http/http.dart' as http;
Future<UserProfile> getUserProfile(String userId) async {
final url = 'https://example.com/api/users/$userId';
final response = await http.get(url);
throwIfNoSuccess(response);
final jsonBody = json.decode(response.body);
return UserProfile.fromJson(jsonBody);
}