Flutter - Is it possible to extract data from a Future without using a FutureBuilder?

Question

I'm reading in user-provided input (in this case a zip code) from a TextField that I need to check against a database for validity. However, I need to make an asynchronous database query inside of the submit button's (a RaisedButton in this case) onPressed: () {} lambda function. In most programming languages, this is a fairly straightforward and simple task. The problem I'm running into in Flutter, however, is the fact that Future objects returned from asynchronous database queries can only be consumed by FutureBuilder objects which in turn only return Widget objects. I simply need a String returned that I can then use to either pass to a new route via a MaterialPageRoute object, or display an error to the user without changing routes. Is there any way to do this with Flutter? Returning a Widget is useless to me as I don't want to create a new Widget for display. I am using Flutter 0.3.2 and Dart 2.0.0

As a simplified example of where I need to call the database query:

@override
Widget build(Buildcontext context) {
    return new Column(
        mainAxisAlignment: MainAxisAlignment.center,
        children: <Widget>[
            new Container(
                padding: const EdgeInsets.all(16.0),
                child: new TextField(
                    keyboardType: TextInputType.number,
                    controller: _controller,
                    decoration: new InputDecoration(
                    hintText: 'Zip Code',
                ),
                onSubmitted: (string) {
                  return string;
                },
              ),
            ),
            new RaisedButton(
                onPressed: () {
                        // use regex to test against user input
                        if (_controller.text != null && _controller.text.isNotEmpty) {
                            RegExp zipCodeRegExp = new RegExp(r"^(\d{5})$");

                            // if the user input validates...
                            if (zipCodeRegExp.hasMatch(_controller.text)) {
                            zipCode = _controller.text;

                           // need to perform database query here and return a string, not a Widget

                            } else {
                               // an else condition here
                            }
                        } else {
                           // an else condition here
                        }
                    }
                }
            ),
        ],
    );
}

Perhaps I'm not following the "mantra" of Flutter? I appreciate your consideration and input on this.

Answer 1

FutureBuilder is just a convenient helper to get the widget tree rebuilt when a Future completes.

You can use

funcThatReturnsFuture().then((result) {
  print(result);
  setState(() {
    someVal = result;
  })
})

or

Future funcThatMakesAsyncCall() async {
  var result = await funcThatReturnsFuture();
  print(result);  
  setState(() {
    someVal = result;
  })
}

The main limitation is that you can't return the value directly to the caller without a Future, because there is no way to get back from async execution to sync execution.