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

I am trying to output title (string) and list of items (widgets), but it is showing two errors.
one is

>element type 'List<widget>' can't be assigned to the list type 'Widget'** and second **the argument type "gridview" can't be assigned to the parameter type "iterable<widget>".

    List<Widget> categoriesWidgets;

    String categoryCaption,
    final List<Widget> result = <Widget>[];

    final Padding categoryTitleWidget = Padding(
    padding: const EdgeInsets.fromLTRB(0, 10, 0, 10),
    child: Text(categoryCaption));

    final GridView results = GridView.count(crossAxisCount: 2,
        children: <Widget>[result]
    );

    categoriesWidgets.add(categoryTitleWidget);
    categoriesWidgets.addAll(results);

    }

You are trying to create array of list of Widget. But the expected is list of widget.

Change

 children: <Widget>[result]

to

 children: result

Edit: "grid view can't be assigned to parameter type iterable"

Change the following code to:

categoriesWidgets.addAll([results]); // add results within []

The results is a single widget GridView, it should use add instead of addAll.

  final GridView results = GridView.count(crossAxisCount: 2,children: result);
  categoriesWidgets.add(categoryTitleWidget);
  categoriesWidgets.add(results);