I have a function A() which return a string and I need to receive the string and print the string using then() method in dart
Future<String> A() async {
return "Hello";
}
await A().then((value) => print(value));
I want to get the "Hello" printed but it prints null. How to do this ?
await should be used in an async function. But you have used await outside of the async function.
Try removing await outside.
Future<String> A() async {
return "Hello";
}
A().then((value) => print(value));
Related
Following is my code. I'm trying to get all the 'Babies' which are in documents:
class _HomePageeState extends State<HomePagee> {
String t_babies = getCount().toString();
}
Future getCount() async {
return FirebaseFirestore.instance.collection('Babies').snapshots().length;
}
Instead I get this error: instance of \_future\<int\>
Here is my Database. I expect to get 2 counts:
You need to use await when getting Future values and also you should pass Future and the type Future<int>:
Future<int> getCount() async {
return await FirebaseFirestore.instance.collection('Babies').snapshots().length;
}
and also get the method using await but inside and async function:
void example() async { // <---- here the async you need to add to use await
int babiesLength = await getCount(); // here use await
}
You should use setState to update the string , because the fetch takes time as it involves network.
String t_babies = '';
Future<void> _getCount() async {
setState((){
t_babies = FirebaseFirestore.instance.collection('Babies').snapshots().length.toString();
});
}
#override
void initState() {
super.initState();
_getCount();
}
How can i return a string from a future function?
Future<String> functionA() async {
var x = await fetchX();
return x;
}
Future<String> fetchX() {
return Future.delayed(Duration(seconds: 4), () => 'example');
}
Future<String> la() async {
print(await functionA()); //this works correctly
return await functionA(); //this return always an instance of Future
}
How can i return "example" from the future function, there is a method to do it, and where is my error?
Future<String> fetch() async {
return
http.get('url')
.then((response) => response.body);
}
That way you can sneak a .catchError into there. :)
You need to specify what your function will return. All you have to do is add Future to the beginning of the method.
Future<String> fetch() async {
final response = await http.get('url');
String conteggio = response.body;
return conteggio;
}
And you have to do this in a method. You can only assign constant values in fields other than methods.
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'm trying to pass as parameter of a method, a function that returns Future<Response>.
I tried to do
Future<String> _execute(Function<Future<Response>>() function) async { }
but it does not even compile.
What's the correct syntax?
You can do it like this,
Future<String> _myFunction(Future<Response> Function() function) {
...
}
You just need to specify that your parameter is a Function:
Future<bool> kappa() async{
await Future.delayed(Duration(seconds: 1));
return true;
}
Future<bool> foo(Function f) async{
var k = await f();
return k;
}
void main() async{
print(await foo(kappa));
}
This will print true. In your case, your function parameter can be:
Future<String> _execute(Function function) async { }
I have following class.
class Element {
Future<Element> findById(var id)async {
await networkRequest();
return this;
}
Futute<Element> click() async {
await networkRequest();
return this;
}
}
I want to achieve the something like.
main() async {
var element = Element();
await element.findyById("something").click();
}
But I'm not able to do so because element.findById() returns future. How can I chain these async methods.
While there's no special syntax to chain futures, there are two semantically equivalent ways to do what you want:
1) Two separate await calls:
await element.findById("something");
await click();
2) Chaining with then:
await element.findById("something").then(() => click());
Use this,
await (await Element().findById("1")).click();
final el = await element.findyById("something");
await el.click();