CODEWITHSUNDEEP
functionflutterdartparametersoptional-parameters
Chris
Chris

Reputation: 2284

Flutter function with named and optional parameters

I have a function that should have three required and in best case named parameters. The last one ("finished") should be optional. I tried it like this:

static void showOverlay(BuildContext context, String text, bool successfull,
  [VoidCallback? finished]) {}

but Flutter is complaining:

Avoid positional boolean parameters

The weird thing is that it is only complaining about the bool successfull. What am I doing wrong here and how can I fix this?

Upvotes: 12

Views: 16528

Answers (3)

Phake
Phake

Reputation: 1349

Named parameters are optional by default. So in your case it would be:

static void showOverlay({BuildContext context, String text, bool successfull, VoidCallback? finished}) {}

Notice the {} in the constructor, this makes your parameters named and optional. By using @required in front of your declaration, you can differentiate between required and not required.

Upvotes: 11

Moaid ALRazhy
Moaid ALRazhy

Reputation: 1744

you can use it like this using positional parameters

 void showOverlay(BuildContext context, String text, bool successful, [VoidCallback finished]) {}

or like this using named parameters

void showOverlay({@required BuildContext context, @required String text, @required bool successful, VoidCallback finished}) {}

and dart is complaining becuase named parameters is best practice as mentioned in dart docs

Positional boolean parameters are a bad practice because they are very ambiguous. Using named boolean parameters is much more readable because it inherently describes what the boolean value represents.

BAD:

Task(true);
Task(false);
ListBox(false, true, true);
Button(false);

GOOD:

Task.oneShot();
Task.repeating();
ListBox(scroll: true, showScrollbars: true);
Button(ButtonState.enabled);

Upvotes: 3

ambiguous58
ambiguous58

Reputation: 1411

Named parameters are optional unless they’re specifically marked as required. Below, all four of your parameters are named. Three are required while one of them is optional.

static void showOverlay({required BuildContext context, required String text, 
  required bool successfull, VoidCallback? finished}) {}

Upvotes: 1

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