The element type 'List<CustomCheckbox>' can't be assigned to the list type 'Widget'

Issue

I have errors "The element type 'List < CustomCheckboxTile >' can't be assigned to the list type 'Widget'" and "Expected to find ','"

The following code is responsible for the dropdown list of items.

class........
bool isClicked=false;
.....
@override
  Widget build(BuildContext context) {
    return SimpleDialog(
      children: [
        Column(
          mainAxisSize: MainAxisSize.min,
          crossAxisAlignment: CrossAxisAlignment.stretch,
          children: [
            Column(children: [
              InkWell(
                  onTap: () {
                    setState(() {
                      isClicked = !isClicked;
                    });
                  },
                  child: Row(children: [
                    Text("Select a brand".toString()),
                    isClicked
                        ? const Icon(Icons.arrow_circle_down)
                        : const Icon(Icons.arrow_circle_up)
                  ])),
              !isClicked
                  ? Container()
                  : ...brands.map((el) =>
                  CustomCheckboxTile(
                    value: filters['brand']?.contains(el) ?? false,
                    label: el,
                    onChange:(check) => _handleCheckFilter(check, 'brand', el),
                  ),
              ).toList()
          ]),
 ........

The code below represents custom checkbox and responsible for selecting elements

    class CustomCheckboxTile extends StatelessWidget {
  final String label;
  final bool value;
  final void Function(bool)? onChange;

  const CustomCheckboxTile({
    Key? key,
    required this.label,
    required this.value,
    this.onChange,
  }) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Row(
      children: [
        Checkbox(
          visualDensity: VisualDensity.compact,
          value: value,
          onChanged: (_) {
            if(onChange != null) {
              onChange!(!value);
            }
          },
        ),
        Text(label),
      ],
    );
  }
}

How can I fix these errors?

Solution

For the first error, you have a ternary operator that returns two different types, one is a Widget (Container), and one is a List (the list of CustomCheckboxTiles). Even though separately, these would both be assignable to the children property of Column, you can't do that in a ternary. You could change it to

!isClicked
? ...[Container()]
: ...brands.map((el) =>
  CustomCheckboxTile(
    value: filters['brand']?.contains(el) ?? false,
    label: el,
    onChange:(check) => _handleCheckFilter(check, 'brand', el),
  ),
).toList()

and it should work, since now both sides of the ternary return List.

Answered By - Andrew