I'm getting a type 'Future<dynamic>' is not a subtype of type 'Future<String>'
I am simply trying to use a FutureBuilder in conjunction with SharedPreferences to return a string that I have previously stored using SharedPreferences.
Flutter : 'Future <dynamic>' is not a subtype of type bool
This stack overflow answer is doing the exact same thing as what I'm doing yet I have an error?
Widget build(BuildContext context) {
return FutureBuilder<String>(
future: getRoleFuture(),
builder: (context, snapshot) {
if(snapshot.data == false) {
return Text("No data");
}
else {
return Text(snapshot.data);
}
}
);
}
getRoleFuture() async {
var sp = await SharedPreferences.getInstance();
return sp.getString("role");
}
The reason is that you used snapshot.data as bool in this line
if(snapshot.data == false) {
return Text("No data");
}
where as you set the Future return type as string
maybe if you do this:
if(snapshot.data == null || snapshot.data == '') {
return Text("No data");
}
else {
return Text(snapshot.data);
}
Check the snapshot with hasData.
if(snapshot.hasData == false)
Gives the return type.
Future<String> getRoleFuture() async {
var sp = await SharedPreferences.getInstance();
return sp.getString("role");
}
In you FutureBuilder future pass a refrence to your function:
future: getRoleFuture, (without the parentheses)
so your code should be something like this:
Widget build(BuildContext context) {
return FutureBuilder<String>(
future: getRoleFuture,
builder: (context, snapshot) {
if(!snapshot.hasData) {
return Text("No data");
}
else {
return Text(snapshot.data);
}
}
);
}
Future<String> getRoleFuture() async {
var sp = await SharedPreferences.getInstance();
return sp.getString("role");
}
We don't use the parentheses in that code because we don't want the function to be called at the point where that code is encountered. Instead, we want to pass a reference to our function into the future.
Related
i made a future function which return bool value, then i used it in the build widget on if condition but the code is always returning the sign in.
can any one help me solving this issue.
Future isExist(uid) async{
var isExist = await Database().checkIfUserExist(uid);
if(isExist == true){
return true;
}
else{
return false;
}
}
#override
Widget build(BuildContext context) {
final user = Provider.of<UserDashboard?>(context);
// return either Home or Authenticate widget
if(user == null){
print("user null");
return SignIn();
}else{
print("user not null");
if(isExist(user.uid) == Future.value(true)){
return Home();
}
}
return SignIn();
}
user is not null and is exist but not taking the correct result.
Future<bool> checkIfUserExist(String adminID) async{
bool isExist = false;
try{
await admin.doc(adminID).get()
.then((doc) => isExist = doc.exists);
return isExist;
}catch(e){
print(e);
return isExist;
}
}
the above function is safe and good because i used it in another screen and worked.
Try using FutureBuilder for future method.
FutureBuilder<bool>(
future: isExist(uid), // use a state variable for statefulwidget
builder: (BuildContext context, AsyncSnapshot<String> snapshot) {
if (snapshot.hasData) {
if(snapshot.data) return Home();
else return SignIn();
}
return CircularProgressIndicator();
}
More about using FutureBuilder
I am trying to check the internet connection of the mobile device. I am using below code to check the connectivity.
import 'package:flutter/material.dart';
import 'package:internet_connection_checker/internet_connection_checker.dart';
class RedirectPage extends StatelessWidget {
final int? status;
#override
Widget build(BuildContext context) {
bool? isDeviceConnected;
() async {
print("a");
print(123);
isDeviceConnected = await checkConnection();
print(888);
};
if (isDeviceConnected != null && isDeviceConnected == false) {
return AppNetworkConnectivityHome();
} else{
return HomePage();
}
}
}
print(isDeviceConnected); //giving null for the first time and true or false on the second time.
Future<bool?> checkConnection() async {
bool a = false;
a = await InternetConnectionChecker().hasConnection;
print(a);
return a;
}
how to force wait for the await function to complete
You'd have to await the method call. You've currently defined it as an anonymous function, so depending on where and how you execute it there will be some differences. But it will work if you instead do something like this:
Future<bool?> myMethod() async {
return await InternetConnectionChecker().hasConnection;
}
...
print(await myMethod());
You can't call async function in build method, you need to use FutureBuilder like this:
return FutureBuilder<bool>(
future: checkConnection(),
builder: (context, snapshot) {
switch (snapshot.connectionState) {
case ConnectionState.waiting:
return Text('Loading....');
default:
if (snapshot.hasError) {
return Text('Error: ${snapshot.error}');
} else {
bool data = snapshot.data ?? true;
if (!data) {
return AppNetworkConnectivityHome();
} else{
return HomePage();
}
}
}
},
)
I am trying to get the value from firestore and use it on my Switch widget. The indicator that I am trying to read on this switch is bool (true or false only). However it is not working, getting this error: type 'Null' is not a subtype of 'bool'
Here is my FetureBuilder code wrapped on my Switch:
FutureBuilder<bool>(
future: getShipValue(),
builder: (context, snapshot) {
if (snapshot.hasData == true) {
setState(() {
isSwitch = true;
});
}
return CupertinoSwitch(
value: isSwitch,
onChanged: (val) {
handleSwitch(val);
},
);
}),
Here is my Function that I am referencing:
Future<bool> getShipValue() async {
return await FirebaseFirestore.instance
.collection('OrderDetails')
.doc(order.orderId)
.get()
.then((value) {
return value.data()!['ShippedInd'];
});
}
Please let me know what am I doing wrong. Many thanks!
if (snapshot.hasData) {
if(snapshot.data){
setState(() {
isSwitch = true;
});
}
} else{
// Do sth else
}
The issue is solved now. As many pointed, I needed to handle the bool(true/false) and such is my FutureBuilder code that worked.
Thank you all!
Future<bool> getSwitchState() async {
isSwitch = await FirebaseFirestore.instance
.collection('OrderDetails')
.doc(order.docid)
.get()
.then((value) {
//return value.data()!['ShippedInd'] == true;
// print(value.data()!['ShippedInd']);
return (value.data()!['ShippedInd'] == true) ? true : false;
});
return isSwitch;
}
I am trying to work with different user roles and after logging in they should be directed to different pages however the futurebuilder I am trying to use to do so returns null. The element.data['role'] is correct and is being printed out before the future is returned but is not returned to the futurebuilder.
Future<String> getUserRole() async {
final result = await FirebaseAuth.instance.currentUser().then(
(user) async {
await Firestore.instance.collection("Users").getDocuments().then(
(docs) {
docs.documents.forEach((element) {
print(element.documentID);
print(user.uid);
if (element.documentID == user.uid) {
print(element.data['role']);
return element.data['role'];
}
});
},
);
},
);
return result;
}
#override
Widget build(BuildContext context) {
return FutureBuilder(
future: getUserRole(),
builder: (ctx, AsyncSnapshot<String> futureResult) {
if (futureResult.connectionState == ConnectionState.waiting) {
return Scaffold(
body: Center(
child: CircularProgressIndicator(),
),
);
} else if (futureResult.hasError) {
Center(
child: Text("Error"),
);
} else if (futureResult.hasData) {
print("BUILDER");
print(futureResult.data);
if (futureResult.data == "Employer") {
return EmployerTabsScreen();
} else {
return EmployeeTabsScreen();
}
} else {
return Text("NONE");
}
},
);
}
Try to call return at all iterations and add a null (or other value) for handling situation where you are not returning a data:
Future<String> getUserRole() {
return FirebaseAuth.instance.currentUser().then((user) {
return Firestore.instance.collection("Users").getDocuments().then((docs) {
var role = null;
docs.documents.forEach((element) {
print(element.documentID);
print(user.uid);
if (element.documentID == user.uid) {
print(element.data['role']);
role = element.data['role'];
}
});
return role;
});
});
}
Because you mix randomly "async/await" with "then"-callbacks.
Guess its not wrong to do that, but like in your example, its totally anreadable and makes everything harder than it could be.
At First:
final result = await FirebaseAuth.instance.currentUser().then(
(user) async {
If you declare something as "await", you dont need a callback. You should declare the result right. If you want to do something with the result, make the new request as an await aswell. Thats it. If you have this response, take it and lambda or foreach it.
The last step is, check what you got and return it.
It makes no sense to "await" something when you make "promises" (said in javascript)
I am having a problem displaying asynchronous data in a text widget.
I'm doing two chained asynchronous methods to search for the coordinates and then search for the city from the smartphone:
Future<String> _getCity() async {
Future<Position> pos = Geolocator().getCurrentPosition(desiredAccuracy: LocationAccuracy.low);
String city = "";
pos.then((result) {
return result;
})
.then((result) async {
List<Placemark> listPlacemark = await Geolocator().placemarkFromPosition(result);
return listPlacemark;
})
.then((result) {
return result.first;
})
.then((result) {
city = result.subAdministrativeArea;
// print( city ); -> Here it's showing correct data in console
});
return city;
}
The city appears on the console in that print command that is commented out.
To fill the text widget I'm doing this:
Padding(
padding: EdgeInsets.all(12),
child: FutureBuilder<String>(
future: _getCity(), // a Future<String> or null
builder: (BuildContext context, AsyncSnapshot<String> snapshot) {
switch (snapshot.connectionState) {
case ConnectionState.none:
return Text('Error loading location');
case ConnectionState.waiting:
return Text('Waiting...');
default:
if (snapshot.hasError) {
return Text('Error loading location');
} else {
return Text(snapshot.data);
}
}
},
),
),
I called the _getCity method inside the initState method and it also worked.
The waiting message has already appeared but now everything is blank, what is missing?
I thank you for your attention!
Even if you return a value from the callback of then(), the value is not returned from _getCity(). You need to return Future.
Future<String> _getCity() async {
Future<Position> pos = Geolocator().getCurrentPosition(desiredAccuracy: LocationAccuracy.low);
return pos.then((result) {
return result;
}).then((result) async {
List<Placemark> listPlacemark = await Geolocator().placemarkFromPosition(result);
return listPlacemark;
}).then((result) {
return result.first;
}).then((result) {
return result.subAdministrativeArea;
});
}
By the way, do you need so many thens?
I've never used Geolocator(), so this is just a guess, but some of them may be removed because it looks like listPlacemark, result.first and result.subAdministrativeArea are not Future and you just want to extract a value from List<Position>. If my guess is right, the following will do.
Future<String> _getCity() async {
Future<Position> pos = Geolocator().getCurrentPosition(desiredAccuracy: LocationAccuracy.low);
return pos.then((result) async {
List<Placemark> listPlacemark = await Geolocator().placemarkFromPosition(result);
return listPlacemark.first.subAdministrativeArea;
});
}