What's the best practice to keep all the const

问题:

What's the best programming practice to

create a constant class in Flutter

to keep all the application constants for easy reference. I know that there is const keyword in Dart for creating constant fields, but is it okay to use static along with const, or will it create memory issues during run-time.

class Constants {
static const String SUCCESS_MESSAGE=" You will be contacted by us very soon.";
}

回答1:

While there are no technical issues with static const, architecturally you may want to do it differently.

Flutter tend to not have any global/static variables and use an InheritedWidget.

Which means you can write:

class MyConstants extends InheritedWidget {
  static MyConstants of(BuildContext context) => context. dependOnInheritedWidgetOfExactType<MyConstants>();

  const MyConstants({Widget child, Key key}): super(key: key, child: child);

  final String successMessage = 'Some message';

  @override
  bool updateShouldNotify(MyConstants oldWidget) => false;
}

Then inserted at the root of your app:

void main() {
  runApp(
    MyConstants(
      child: MyApp(),
    ),
  );
}

And used as such:

@override
Widget build(BuilContext context) {
  return Text(MyConstants.of(context).successMessage);
}

---

This has a bit more code than the static const, but offer many advantages:

• Works with hot-reload
• Easily testable and mockable
• Can be replaced with something more dynamic than constants without rewriting the whole app.

But at the same time it:

1. Doesn't consume much more memory (the inherited widget is typically created once)
2. Is performant (Obtaining an InheritedWidget is O(1))

回答2:

My preferred solution is to make my own Dart library.

Make a new dart file named constants.dart, and add the following code:

library constants;

const String SUCCESS_MESSAGE=" You will be contacted by us very soon.";

Then add the following import statement to the top of any dart file which needs access to the constants:

import 'constants.dart' as Constants;

You may need to run flutter pub get for the file to be recognized. And now you can easily access your constants with this syntax:

String a = Constants.SUCCESS_MESSAGE;

回答3:

That's completely up to you.
Using static has no disadvantages.
Actually const is required for fields in a class.