Accesing screen width outside of context - flutter

Question

I am creating a class for notifications that is outside of context using bot_toast, which will be called on API errors and such. I need to leave a margin that is relative to the screen width, but I don't have the context here. I could pass the context around, it doesn't seem like the best option.
So I am ending up with something like this
Function CustomToast (message) {
return BotToast.showAttachedWidget(
attachedBuilder: (_) => Align(
alignment: Alignment.topRight,
child: Container(
margin: new EdgeInsets.only(top: 25, right: 25.0),
color: Colors.blue,
child: Padding(
padding: const EdgeInsets.all(8.0),
child: Text(
message,
),
),
),
),
duration: Duration(seconds: 20),
target: Offset(520, 520));
}
I need to set the righ margin as a percentage. How would I access the screen width here? is it possible without context? Any suggestion is welcome, even a change of toast library

Answer 1

Perhaps an app level model. Once you have a context, you can set the screen resolution for later retrieval of calculated percentage. I use this approach frequently.
class ScreenInfoViewModel {
List<String> _setupCompleted = [];
String appName;
String packageName;
String version;
String buildNumber;
double screenWidth;
ScreenInfoViewModel() {
init();
}
init() async {
var packageInfo = await PackageInfo.fromPlatform();
appName = packageInfo.appName;
packageName = packageInfo.packageName;
version = packageInfo.version;
buildNumber = packageInfo.buildNumber;
}
bool _smallScreen = false;
bool _mediumScreen = false;
bool _largeScreen = false;
void setScreenSize(double this.screenWidth, double diagonalInches) {
_smallScreen = diagonalInches < 5.11;
_mediumScreen = !_smallScreen && diagonalInches <= 5.6;
_largeScreen = diagonalInches > 5.6;
}
bool get isSmallScreen => _smallScreen;
bool get isMediumScreen => _mediumScreen;
bool get isLargeScreen => _largeScreen;
String get screenSize {
String size = 'S';
if (_mediumScreen) size = 'M';
if (_largeScreen) size = 'L';
return size;
}
}
I use it this way:
class SetupScreenInfo extends HookWidget {
// Use GetIt package to retrieve the model
final ScreenInfoViewModel _s = locator();
final _scaffoldKey = new GlobalKey<ScaffoldState>();
#override
Widget build(BuildContext context) {
/// This is the first 'context' with a MediaQuery, therefore,
/// this is the first opportunity to set these values.
/// widthPx and diagonalInches are from sized_context package.
_s.setScreenSize(context.widthPx, context.diagonalInches);
WidgetsBinding.instance.addPostFrameCallback((_) {
if (context == null) return;
Navigator.pushReplacementNamed(context, splashRoute);
});
return SafeArea(
child: Scaffold(
key: _scaffoldKey,
body: Material(color: Colors.yellow[300]),
),
);
}
}
Finally, SetupScreenInfo is my initial route from my MaterialApp.
This code is an edit of my production code and has not been tested and is not a runnable example.
Hope this help generate some thought.