Flutter 2.0 / Dart - How to create a constructor with optional parameters?

Question

I created a class and want some of the parameters to be optional, but can't figure out how to do it.

class PageAction {
  PageState state;
  PageConfiguration page;
  List<PageConfiguration> pages;
  Widget widget;

  PageAction({
    this.state = PageState.none,
    this.page, // Optional
    this.pages, // Optional
    this.widget, // Optional
  });

I get the suggestion to add "required", but that is not what I need. Can someone help and explain please?

Martijn · Accepted Answer · 2021-08-24T15:07:29.090

7

The title says Flutter 2.0 but I assume you mean with dart 2.12 null-safety. In your example all the parameters are optional but this will not compile cause they are not nullable. Solution is to mark your parameters as nullable with '?'.

Type? variableName // ? marks the type as nullable.

class PageAction {
  PageState? state;
  PageConfiguration? page;
  List<PageConfiguration>? pages;
  Widget? widget;

  PageAction({
    this.state = PageState.none,
    this.page, // Optional
    this.pages, // Optional
    this.widget, // Optional
  });

edited Aug 24 '21 at 15:07

answered Apr 09 '21 at 14:42

Martijn

114
5

Thanks a lot, I edited the post to fit it to your answer. Seems to work so far – Civan Öner Apr 09 '21 at 14:48
1

you're welcome :) good luck with your project. – Martijn Apr 09 '21 at 14:55

score 0 · Answer 2 · answered Sep 07 '21 at 01:59

0

I have shared a detailed information on constructors, Please refer my answer https://stackoverflow.com/a/69081615/563735

answered Sep 07 '21 at 01:59

Rohit Mandiwal

10,258
5
70
83

Flutter 2.0 / Dart - How to create a constructor with optional parameters?

2 Answers2