将变量传递给扩展另一个类的Flutter小部件

Question

I am using the fluter_google_places Flutter plugin. I am trying to pass a callback function into the widget, such that when a Place is tapped, the callback function is called:

class GooglePlaces extends PlacesAutocompleteWidget {
    final Function callback;

    GooglePlaces(this.callback)
        : super(
            apiKey: kGoogleApiKey,
            sessionToken: Uuid().generateV4(),
            language: "en",
            );

    @override
    _GooglePlaces createState() => _GooglePlacesState();
    }

    class _GooglePlacesState extends PlacesAutocompleteState {
    final GlobalKey<ScaffoldState> scaffoldKey = GlobalKey<ScaffoldState>();

    void startSearch() async {
        Prediction p = await PlacesAutocomplete.show(
        context: context,
        apiKey: kGoogleApiKey,
        mode: Mode.overlay,
        language: "en",
        );

        displayPrediction(p);
    }

    Future<Null> displayPrediction(Prediction p) async {
        if (p != null) {
            widget.callback(); // Call callback function
        }
    }
}

Creating the widget in another file:

void myCallback() {
    // ...
}

GooglePlaces(myCallback);

However the widget.callback(); displays the error: The method 'callback' isn't defined for the class 'PlacesAutocompleteWidget'

How do I call the callback function from the widget?

Answer 1

You're running into this error because class _GooglePlacesState extends PlacesAutocompleteState not State<GooglePlaces> . So widget.callback() refers to a state of PlacesAutocompleteWidget .

There's two solutions here:

1) The cheap way out:

Pass the callback to the state like so: _GooglePlaces createState() => _GooglePlacesState(callback);

and add the callback to the state constructor.

2) (As stated above) Change _GooglePlacesState to extend State<GooglePlaces> .