异步等待而非等待完成

Question

我通读了Dart/flatter中的Async/Await/then，试图理解为什么aysnc函数中的Await不会等到完成后再继续。在我的UI中，有一个按钮调用一个异步方法来返回一个位置，该位置总是返回null，并且不等待函数完成。

   onChanged: (newValue) async {
      setState(() {
        _selectedLocation = newValue;
      });
      if (_selectedLocation == "Set Location") {
        location = await runPlacePicker(context);    // <- Calling the method here
        _selectedLocationText = location.lat.toString();
      }

  Future<Location> runPlacePicker(context) async {   // <- Should return a Location value after popup
    Timer _throttle;
    PlacePicker result;
    Location location;
    Navigator.push(
        context,
        MaterialPageRoute(
            builder: (context) => PlacePicker(
                  apiKey: "",
                  onPlacePicked: (result) {
                    print(result.formattedAddress);
                    Navigator.of(context).pop();
                    location = result.geometry.location;
                    return location;
                  },
                  initialPosition: LatLng(0,0),
                  resizeToAvoidBottomInset: true,
                  useCurrentLocation: true,
                )
        )
    );
    if (location == null) {
      return null;
    } else {
      return location;
    }
  }

该函数将调用推送到一个新的UI页面，该页面选择一个位置，并应返回一个结果。如何使该函数等待结果？我不是在使用异步吗？

Answer 1

您可以使用Navigator.of（上下文）. pop（位置）从PlacePicker返回结果。

代码可以简化为：

Future<Location> runPlacePicker(context) async {
  final Location location = await Navigator.push(
    context,
    MaterialPageRoute(
      builder: (context) => PlacePicker(
        apiKey: "",
        onPlacePicked: (result) {
          Navigator.of(context).pop(result.geometry.location);
        },
        initialPosition: LatLng(0,0),
        resizeToAvoidBottomInset: true,
        useCurrentLocation: true,
      )
    )
  );
  return location;
}