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
Related
I am getting some data from API in flutter. I am trying to decode the data using json.decode() but this decode function gives me the following error:
Closure: () => String from Function 'toString'
Here's my code:
Future<Product> createOrder() async {
var client = new http.Client();
var productModel = null;
try {
var response = await client
.get(Uri.https('butterbasket.onrender.com', Strings.createOrderUrl));
if (response.statusCode == 200) {
var body = response.body;
print("Body: $body");
var jsonMap = json.decode(body);
var productModel = Product.fromJson(jsonMap);
}
} catch (e) {
print("Exception: ${e.toString}");
}
return productModel;
}
Here is the Error Debug Console:
You are running into issues because the data you are loading in is an array, but the model is an object. You'll need to do something like the following:
final List jsonProducts = json.decode(body)
final List<Product> products =
jsonProducts.map((jsonProduct) => Product.fromJson(jsonProduct)).toList();
and then if you only need the first item you can do:
final Product product = products[0]
But don't forget to check if the array is big enough.
Your Future function must return an optional Product?, otherwise your future will never find a result as you are declaring it inside the function.
Instead of:
Future<Product> createOrder() async {}
Use:
Future<Product?> createOrder() async {}
Finally your async snapshot and FutureBuilder type should be of type <Product?>.
Still new to Flutter :(. Can anyone help...
I have a class that stores a bunch of project information. One part of this is a list of topics (for push notification), which it grabs from a JSON file.
I apply a getter for the list of topics, and when getting it it calls an async function which will return a List
Future<List<String>> _pntopics() async{
final _json = await http.get(Uri.parse(_topicsUrl));
if (_json.statusCode == 200) {
return (jsonDecode(_json.body));
}else {
return [""];
}
}
Future<List<String>> get topics => _pntopics();
In my main.dart file, it calls this value like so...
Future<List<String>> _topiclist = await projectvalues.topics;
The response is however empty, pressumably because it is a Future - so it is grabbing the empty value before it is filled.
But I can't remove the "Future" part from the async method, because asnc methods require a Future definition.
Then I decided to remove the declarations entirely:
_pntopics() async{
final _json = await http.get(Uri.parse(_topicsUrl));
if (_json.statusCode == 200) {
return (jsonDecode(_json.body));
}else {
return [""];
}
}
get topics => _pntopics();
and in main.dart, a general declaration...
var _topiclist = await projectvalues.topics;
...and this works!
So what declaration should I actually be using for this to work? I'm happy to not use declarations but we're always to declare everthing.
You should return back Future<List<String>> return types to the function and the getter but for _topicslist you must use var, final or List<String> declaration because:
(await Future<T>) == T
i.e.
var _topiclist = await projectvalues.topics; // The type of _topiclist is List<String>
final _topiclist = await projectvalues.topics; // The type of _topiclist is List<String>
UPDATE
Your code should be:
Future<List<String>> _pntopics() async{
final _json = await http.get(Uri.parse(_topicsUrl));
if (_json.statusCode == 200) {
return List<String>.from(jsonDecode(_json.body));
}else {
return <String>[""];
}
}
Doing this you force _pnptopics returns List<String> as jsonDecode returns List<dynamic>.
P.S. It is good practice do not use dynamic types where they can be changed to specified types.
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();
}
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