Is there a downside to not making MethodChannels static const in Flutter?

Question

The examples in the Flutter docs have the MethodChannel they are using (to communicate with the native host) declared as static const, directly in the Widget that's using it. To bring some separation into it, I'm trying to lay out my app so that the MethodChannel

1. resides in the BLoCs or even the underlying service layer instead of directly in the Widget, and
2. is instead injected, to make everything easily unit-testable.

Is it a problem (performance-related, bug-inducing, etc.) if the MethodChannel is not static and const?

Solution

The MethodChannel instance where it is defined is const by convention, and to be honest there is little reason for it ever not to be. However, while the typical implementation has the channel defined in the service class, it doesn't have to be. You could also easily define it elsewhere and then pass it to your service class via dependency injection.

DI Init File

const platform = MethodChannel(...);

void initDI() {
  GetIt.I.registerSingleton(platform, "MyMethodChannel");
}

Service File

class PlatformService {
  final MethodChannel platform;

  PlatformService()
    : platform = GetIt().I.get("MyMethodChannel");

  ...
}

Comments

[Abion47]

I'm not sure if there's a practical downside to having multiple instances of a MethodChannel that have the same channel name, but I'm also struggling to see the upside. Each of those instances are going to point to the same platform channel, so there's no reason not to have it be static const, and doing so creates a canonical instance that the program can reuse. You can still use dependency injection even if you declare it static const, so why wouldn't you?

[Paco1]

Unfortunately at least with get_it it's not possible, as far as I know: "Const variables must be initialized with a constant value." It can still be static, just not const. Even if having a static const dependency would lead my main driver for using dependency injection (which is unit testing) ad absurdum anyway, please write up an answer if it is possible and I just don't get it. I'll change my question slightly and accept your answer.

[Abion47]

I still don't understand your use case. There's nothing preventing you from setting up a singleton or a factory in get_it that returns a constant variable.

[Paco1]

Ok, my concrete problem is: my service class needs access to a MethodChannel. My app doesn't only have one channel, so I need to resort to named injection. Now of course I can declare const MethodChannel(...) in get_it, but even then const MethodChannel platform = sl.get("MyMethodChannel"); gives me the error "Const variables must be initialized with a constant value."

[Abion47]

The MethodChannel instance where its originally defined should be constant, but there's no rule stating the reference in your service class has to be.