无法在 Dart 的构造函数中调用 class 方法 class

Question

I am new to Dart programming. Need help in updating the List "items" before instantiating the super class.

import 'package:flutter/material.dart'; import '../util/color_constants.dart';

class CustomBottomNavigatorBar extends BottomNavigationBar{

  final List<BottomNavigationBarItem> items;

  CustomBottomNavigatorBar(
      this.items,   ): super(backgroundColor: ColorConstants.facebook_blue,items: updateListWithDefaultIcons(items));

  List<BottomNavigationBarItem> updateListWithDefaultIcons(){
    items.add(BottomNavigationBarItem(
      label: 'Settings',
      icon: Icon(Icons.settings),
      tooltip: 'Settings',
      backgroundColor: ColorConstants.white,));
    items.add(BottomNavigationBarItem(
      label: 'Profile',
      icon: Icon(Icons.man),
      tooltip: 'Profile',
      backgroundColor: ColorConstants.white,));
    return items;   } }

Here is the error that Dart throws up while compiling the code

The instance member 'updateListWithDefaultIcons' can't be accessed in an initializer. Try replacing the reference to the instance member with a different expression

Answer 1

You can use variable instead of method updateListWithDefaultIcons and pass default on items. and it is recommended not to create items variable that is coming from parent.

class CustomBottomNavigatorBar extends BottomNavigationBar {
  final List<BottomNavigationBarItem> items_;

  CustomBottomNavigatorBar({
    Key? key,
    this.items_ = _updateListWithDefaultIcons,
  }) : super(
          key: key,
          backgroundColor: Colors.cyanAccent,
          items: items_,
        );

  static const List<BottomNavigationBarItem> 
                    _updateListWithDefaultIcons = [
                         BottomNavigationBarItem(...)
                         .... ]
}