Allow ListView.builder() to have leading / trailling elements

list_view_with_extra_elements.dart

import 'package:flutter/material.dart';

class ListViewWithExtraElements<T> extends StatelessWidget {
  final List<T> elements;
  final List<Widget> leadingElements;
  final List<Widget> trailingElements;
  final Widget Function(BuildContext context, T element) itemBuilder;

  ListViewWithExtraElements({
    this.leadingElements = const [],
    this.trailingElements = const [],
    @required this.elements,
    @required this.itemBuilder,
  })  : assert(leadingElements != null),
        assert(trailingElements != null);

  @override
  Widget build(BuildContext context) {
    final totalElements =
        elements.length + leadingElements.length + trailingElements.length;

    return ListView.builder(
      itemBuilder: (ctx, idx) {
        if (idx < leadingElements.length) {
          return leadingElements[idx];
        } else if (idx >= leadingElements.length &&
            idx < leadingElements.length + elements.length) {
          final elementIndex = idx - leadingElements.length;
          return itemBuilder(ctx, elements[elementIndex]);
        } else {
          final trailingIndex = idx - leadingElements.length - elements.length;
          return trailingElements[trailingIndex];
        }
      },
      itemCount: totalElements,
    );
  }
}

Np !