---
id: user_list_core
sidebar_position: 10
title: UserListCore
---

A Widget For Building A List Of Users

### Background

The UI SDK of Stream Chat supplies a `UserListView` class that builds a list of channels fetching
according to the filters and sort order given. However, in some cases, implementing novel UI is necessary
that cannot be done using the customization approaches given in the widget.

To do this, we extracted the logic required for fetching channels into a 'Core' widget - a widget that
fetches channels in the expected way via the usual parameters but does not supply any UI and instead
exposes builders to build the UI in situations such as loading, empty data, errors, and on data received.

### Basic Example

`UserListCore` is a simplified class that allows fetching users while
exposing UI builders.
A `UserListController` is used to load and paginate data.

```dart
class UsersListPage extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: UsersListCore(
        sort: [SortOption('last_active')],
        pagination: PaginationParams(
          limit: 20,
        ),
        errorBuilder: (err) {
          return Center(
            child: Text('An error has occured'),
          );
        },
        emptyBuilder: (context) {
          return Center(
            child: Text('Nothing here...'),
          );
        },
        emptyBuilder: (context) {
          return Center(
            child: CircularProgressIndicator(),
          );
        },
        listBuilder: (context, list) {
          return UsersPage(list);
        }
      ),
    );
  }
}
```

`UsersBloc` must be the ancestor of this widget. This is necessary since
`UserListCore` depends on functionality contained within `UsersBloc`.

The parameters `listBuilder`, `loadingBuilder`, `emptyBuilder` and
`errorBuilder` must all be supplied and not null.

