dart issue trying to initialize a Uint8List variable in a named constructor

Question

import 'dart:typed_data';
class Test {
  Uint8List testKey;
  Test({this.testKey = Uint8List(0)});
}

Gives compile error: Error: Cannot invoke a non-'const' factory where a const expression is expected.

Also tried -- Uint8List.fromList([]); with same result.

How can I do this? Thanks

Dan R · Accepted Answer · 2025-06-04 17:40:13Z

0

In Dart, a default parameter value must be a compile-time constant. Since the class Uint8List does not provide a const constructor, your default value could be a constant object of type List<int> instead:

import 'dart:typed_data';

class Test {
  Uint8List testKey;
  Test({List<int> inputList = const []})  // Note the keyword "const".
    : testKey = Uint8List.fromList(inputList);
}

edited Jun 4 at 17:40

answered Jun 4 at 17:24

Dan R

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1 Comment

user1624503 Jun 4 at 22:53

that worked! Thanks - don't know how long it would have taken to figure that out! Maybe suggest that all the definitions like Uint8List have a static, const named 'empty' for situations like this.

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