FutureBuilder doesnt work when used with SharedPreferences

Question

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");
  }

score 2 · Answer 1 · answered Feb 24 '20 at 01:36

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);
    }

Kahou · Answer 2 · 2020-02-23T21:30:20.697

0

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");
  }

edited Feb 23 '20 at 21:30

answered Feb 23 '20 at 21:16

Kahou

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Same issue, doesn't make a difference – user9754798 Feb 23 '20 at 21:18
This is a problem with Future – user9754798 Feb 23 '20 at 21:19
Gives return type 'Future' . – Kahou Feb 23 '20 at 21:31

Abdelbaki Boukerche · Answer 3 · 2020-02-24T05:07:05.633

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.

FutureBuilder doesnt work when used with SharedPreferences

3 Answers3