A value of type "Future<Null>" can't be assigned to a variable of type "Data" - flutter

Question

I'm trying figured out how to work with future for fetching data over internet. I was trying to write a simple code where I convert Future into "average" data but it doesn't work and I can't get why that's happend.
Here's my code
class Fetch {
Data getData () {
Data data;
data = fetch().then((value) {data = value;}); //here's I'm getting error
}
Future<Data> fetch() async {
int number = await Future.delayed(Duration(seconds: 1), () => 3);
return(Data.fromIt(number));
}
}
class Data{
int date;
Data({this.date});
factory Data.fromIt(int num) {
return Data(
date: num,
);
}
}
After I corrected this part of code error has gone but now getData() returns null instead of value:
Data getData () {
Data data;
fetch().then((value) {data = value;});
return data; //null
}
Thanks

Answer 1

You can make getData an async function, and use the await keyword. It is much easier to understand if you are new to async programming and Futures
Future<Data> getData () async {
final data = await fetch();
// Whatever you want to do with data
return data; // Dont forget to return it back to the caller
}

Answer 2

The data is defined as a Data object, while fetch() returns a Future<Data>, causing the error.
Data data;
data = fetch().then((value) {
data = value;
});
You can not transform a Future object to a synchronous object without awaiting it. You can do this at the UI to get the Future value:
FutureBuilder<Data>(
future: Fetch().fetch(),
builder: (context, snapshot) {
if (!snapshot.hasData) return Container();
Data data = snapshot.data;
return Text(data);
},
)